Foam in the aquatic environment

Abstract

Foams are ubiquitous in the environment, commonly seen as discoloured patches on streams, rivers, lakes and sea water. They often are assumed to be anthropogenic in origin as they are aesthetically unpleasant, yet they frequently appear in pristine environments indicating a natural origin. In contrast to "hidden" chemical pollution, e.g. heavy metals, pesticides etc. the visibility of foam alarms the public. To derive more information on foam in freshwaters and marine ecosystems, a literature review was performed. Alongside with some basic considerations on the formation of foam, on methods to measure foam formation and on the legal aspects of foam on surface waters, the ecological importance of foam in the aquatic environment is discussed in this paper.

Full text

This article appeared in a journal published by Elsevier. The attached
copy is furnished to the author for internal non-commercial research
and education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright

Author's personal copy
Foam in the aquatic environment
Katerina Schilling
a,b,
*, Matthias Zessner
a,b
a
Institute for Water Quality, Resources and Waste Management, Vienna University of Technology, Karlsplatz 13/226, 1040 Vienna, Austria
b
The Centre for Water Resource Systems, Vienna University of Technology, Karlsplatz 13/226, 1040 Vienna, Austria
article info
Article history:
Received 10 January 2011
Received in revised form
1 June 2011
Accepted 1 June 2011
Available online 28 June 2011
Keywords:
Foam formation
Surface microlayer
Foam enrichment
Sea foam
abstract
Foams are ubiquitous in the environment, commonly seen as discoloured patches on
streams, rivers, lakes and sea water. They often are assumed to be anthropogenic in origin
as they are aesthetically unpleasant, yet they frequently appear in pristine environments
indicating a natural origin. In contrast to “hidden” chemical pollution, e.g. heavy metals,
pesticides etc. the visibility of foam alarms the public.
To derive more information on foam in freshwaters and marine ecosystems, a literature
review was performed. Alongside with some basic considerations on the formation of
foam, on methods to measure foam formation and on the legal aspects of foam on surface
waters, the ecological importance of foam in the aquatic environment is discussed in this
paper.
ª2011 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4356
2. Foam characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4356
2.1. Foam formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4356
2.2. Surface active compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4357
2.3. Surface microlayer (SML) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4357
2.4. Foam stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4357
3. Methods to quantify foam formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4358
4. Legal aspects of foam formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4359
4.1. Regulation of instream foam formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4359
4.2. Regulation of foam emitted by point sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4359
5. Foam formation in wastewater systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4359
6. Relevance of foam on surface waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4360
6.1. Enrichment of foams in lakes and rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4360
6.1.1. Metals ....................................................................................... 4360
6.1.2. Carbon and nutrients ........................................................................... 4361
6.1.3. Lipids and hydrocarbons ........................................................................ 4361
6.1.4. Polychlorinated biphenyl (PCB) ................................................................... 4361
*Corresponding author. Institute for Water Quality, Resources and Waste Management, ViennaUniversity of Technology, Karlsplatz 13/226,
1040 Vienna, Austria. Tel.: þ43 1 58801 22613; fax: þ43 1 58801 22699.
E-mail address: kschilling@iwag.tuwien.ac.at (K. Schilling).
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
water research 45 (2011) 4355e4366
0043-1354/$ esee front matter ª2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2011.06.004

Author's personal copy
6.2. Occurrence and composition of sea foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4361
6.3. Ecological importance of foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4362
6.3.1. Toxicity of foam ............................................................................... 4362
6.3.2. Foam as food resource .......................................................................... 4362
6.3.3. Foam as habitat ............................................................................... 4363
6.3.4. Other roles of foam in the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4363
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4363
Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4364
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4364
1. Introduction
Since the implementation of biodegradable detergents and
the proper operation of wastewater treatment plants, it has
been believed that the occurrence of foam on surface waters
was eliminated in Austria and other countries with a well-
developed waste water treatment infrastructure. But still,
the formation of foam in freshwater ecosystems such as rivers
and lakes has been reported several times. In this context
foam is linked to point source emissions (Defrain and Schulze-
Rettmer, 1989; Madrange et al., 1992; Ruzicka et al., 2009)as
well as natural occurring surfactants derived from algae and
plants (Harrington, 1997; Lu et al., 2006; Shi et al., 2005; Wegner
and Hamburger, 2002). Considerable literature is available on
the occurrence of “sea foam” in marine ecosystems (Ba
¨rlocher
et al., 1988; Ba
¨tje and Michealis, 1986; Craig et al., 1989; Desroy
and Denis, 2004; Eberlein et al., 1985; Maynard, 1968; Seuront
et al., 2006; Velimirov, 1982).
Nevertheless information on foam in the aquatic environ-
ment is limited and sometimes out-dated compared to the
existing literature on the foams linked to various industry-
branches, e.g. food industry (Dale et al., 1999; Piazza et al.,
2008; Vanrell et al., 2007), fire-fighting-industry (Figueredo and
Sabadini, 2003; Tafreshi and Marzo, 1999), cement-industry
(Pedersen et al., 2007), cosmetic- and detergent-industry
(Buzzacchi et al., 2006; Regismond et al., 1998; Zhang et al.,
2004). Other sources of information are investigations on foam
in wastewater treatment processes due to the occurrence of
filamentousbacteria (Blackall et al., 1991; Blackall and Marshall,
1989; Hladikova et al., 2002; La
´nsky´ et al., 2005; Lemmer et al.,
2005; Petrovski et al., 2010; Torregrossa et al., 2005).
Today quality and pollution of surface water is a not only
an issue for scientists, but also policymakers, politicians and
the public in general. Although foam can be used in environ-
mental remediation processes, e.g. in aquifers (Vikingstad,
2006), in water science foam is known to be the polluter, not
the pollution remover. The public exhibits considerable
interest in foams and usually associates them with detergents
or some form of pollution (Mills et al., 1996; Pojasek and
Zajicek, 1978). A psychological investigation demonstrated
that the public associated the presence of foam on surface
waters with pollution which results in a reduced preference to
use the water for recreational purposes or as drinking water
sources (Wilson et al., 1995).
A good example on how foam can provoke public concern
is the formation of foam on an Austrian river close to the
border with Hungary that resulted in an impaired political
relationship due to massive protests from Hungarian locals.
A research study related the foam to the effluent of three
tanning factories, although their wastewater treatment
complied with best available technology and met the legal
requirements (Ruzicka et al., 2009). As a result of the public
concern, the Austrian emission directive for tanneries was
adapted and the implementation of quaternary chemical
treatment became a requirement to prevent instream foam
formation.
This example highlights the increasing public awareness in
terms of water pollution. Certainly, the visibility of foam
addresses the ecological ‘‘conscience” of people more than
‘‘hidden” chemical pollution. In fact, foam is not necessarily
associated with pollution, but can occur naturally in very
pristine environments, e.g. humic waters from rainforests.
The increasing environmental awareness and regulatory
pressures demand a better understanding of the composition,
origin and significance of foam (Napolitano and Richmond,
1995). In consequence, a literature review was carried out to
identify existing information on foam itself, reasons for its
formation and its behaviour in the aquatic environment. This
paper will also deal with methods to measure foam formation,
the existing legislation as well as with the importance and
dangers of foam formation from an ecological perspective.
2. Foam characteristics
2.1. Foam formation
Foam is a dispersion of a gas in a liquid or solid separated by
thin liquid films or lamellae (Heard et al., 2008; Holmberg et al.,
2003). A pure liquid cannot foam unless a surface-active
material is present. A gas bubble introduced below the surface
of a pure liquid will burst immediately as soon as the liquid
drains away. In fact, purity of water can be estimated from the
bubble persistence time when shaking the water sample in
a closed container. A bubble persistence time of even 1 s is an
indication of the presence of surface-active impurities (Pugh,
1996). Consequently, foams are always formed from
mixtures, where one component must be surface active.
A measure of the surface activity is the decrease in surface
tension upon adding the surface-active component to a pure
liquid (Holmberg et al., 2003). Surface-active foaming mate-
rials include particles, polymers, specific absorbed cations or
anions from organic salts etc., most of them cause foaming at
extremely low concentrations (Pugh, 1996).
water research 45 (2011) 4355e43664356

Author's personal copy
A second precondition for foam formation is a source of gas
bubbles (Heard et al., 2008) that must be injected at a higher
rate than the rate at which the liquid between the bubbles can
drain away (Napolitano and Cicerone, 1999). In aquatic
ecosystems mechanical impact is needed to introduce air
bubbles into the water (Poremba, 1991), which can be caused
by cascades or hydraulic structures such as weirs, dams,
spillways and discharge pipes, due to stormy conditions and
the pounding of waves, in areas of strong currents or in areas,
where fresh and salt water mixes (Craig et al., 1989; Ettema
et al., 1989; Fisenko, 2004).
2.2. Surface active compounds
Surface active components or surfactants have a great influ-
ence on the surface or interfacial properties in a solution.
A surfactant is a molecule that has a hydrophobic hydro-
carbon chain and a hydrophilic head group. The surfactant
can be anionic, cationic or zwitterionic. Above the critical
micelle concentration (cmc) the surfactant molecules aggre-
gate in micelles. The micelles have an ordered structure that is
dependent on the hydrophilic and hydrophobic properties of
the surfactant (Vikingstad, 2006).
According to literature several surface-active compounds
can cause foam in the aquatic environment. Natural foams
are usually linked to humic and fulvic acid substances (Ettema
et al., 1989; Napolitano and Richmond, 1995), fine colloidal
particles (Ettema et al., 1989), lipids and proteins originating
from aquatic or terrestrial plants leaching from soil by
precipitations events (Napolitano and Richmond, 1995),
saponins representing a family of plant glycosides (Pojasek
and Zajicek, 1978; Wegner and Hamburger, 2002), the exuda-
tion or decomposition products of phytoplankton containing
carbohydrates and proteins (Ba
¨tje and Michealis, 1986;
Eberlein et al., 1985; Seuront et al., 2006) and the natural
reservoir of organic matter occurring in sediments
(Napolitano and Richmond, 1995). Man-made foam is linked to
phosphates from farm fertilizers (Ettema et al., 1989) and
organic and inorganic (detergents) pollution discharged by
point sources especially from the paper and leather industry
(Ettema et al., 1989; Fisenko, 2004; Madrange et al., 1992;
Ruzicka et al., 2009). In summary, the literature provides
a wide range of foam causing substances, which have been
investigated to greater and lesser extents. Considering the fact
that foam formation is a sum effect of all surface-active
compounds present in the water, in most cases not one
single substance, but a mixture of various components is
responsible for foam (Wegner and Hamburger, 2002).
2.3. Surface microlayer (SML)
In marine and freshwater ecosystems, the airewater
boundary, known as the surface microlayer (SML), constitutes
an important interface between the troposphere and the
underlying water (Ho
¨rtnagl et al., 2010). It is a vehicle for the
transport of inorganic and organic materials between the
atmosphere and the water column (Napolitano and Cicerone,
1999). Substances and particles temporarily or permanently
incompatible with purely aquatic or atmospheric ecosystems,
e.g. natural oils, organic acids and proteins will accumulate in
this zone near the air-water interface. SMLs may also include
components derived from human activities, such as petro-
leum compounds, synthetic surfactants, long-chain alcohols,
synthetic pesticides and herbicides (Napolitano and
Richmond, 1995; Parker and Barsom, 1970). These materials
accumulate in the SML by adsorbing onto bubbles as they rise
through the water column (Harden and Williams, 1989). At the
water surface the bubbles may burst ejecting aerosol droplets
into the air. Under certain conditions emerging bubbles may
not burst instantly, but accumulate on the water surface
producing foam. The aqueous foam phase contains the
surface-active substances accumulated in the SML. Assuming
that a typical foam consists of 90% air and that the mean
thickness of the SML is about 50 mm, 1 L of foam water would
represent 2 m
2
of SML (Napolitano and Cicerone, 1999). Foam
may also be produced by the compression of the SML gener-
ated by wind or as a result of breaking waves at the shoreline
(Ba
¨rlocher et al., 1988; Eisenreich et al., 1978; Harden and
Williams, 1989).
2.4. Foam stability
Due to their high interfacial energy foams are thermody-
namically unstable. The instability has been classified into
two types, which are (1) unstable or transient foams with
lifetime of seconds and (2) metastable or so called permanent
foams with lifetimes measured in hours to days (Pugh, 1996).
Collapsing foams are the result of the bubble coalescence
defined as joining together of two bubbles in a fluid to form
one larger bubble. It can be described as a three-step process:
bubble approach and creation of a thin film, film drainage and
film rupture. In pure water no stable film is formed and coa-
lescence takes only a few milliseconds, whereas surfactants
stabilise bubbles against coalescence leading to foam lifetimes
from seconds to days (Henry, 2010).
The most obvious force acting on foam is gravity causing
drainage of the liquid between the air bubbles. Drainage can
be reduced by either increasing the viscosity of the bulk liquid
or by adding particles (Heard et al., 2008; Holmberg et al., 2003;
Pugh, 1996). Such systems give very stable foams (Holmberg
et al., 2003; Wegner and Hamburger, 2002). The influence of
solid particles on the formation and stability of foam is
dependent on the surfactant type, the particle size and
concentration. Hydrophilic particles present in the aqueous
phase of the foam films are able to enhance foam stability by
slowing down the film drainage. On the other hand, hydro-
phobic particles entering the air-water surfaces of the foam
can cause destabilisation via the bridging-dewetting mecha-
nism (Binks, 2002). According to Pugh (1996) partially hydro-
phobic particles can cause an increase or decrease in foam
stability. Small particles, if not fully wetted, may become
attached to the interface and give some mechanical stability
to the lamella. If completely dispersed, they may cause an
increase in bulk viscosity and stabilise foams. On the other
hand, larger particles having a higher degree of hydropho-
bicity (coal dust, sulphur, non-wetting quartz) may cause
destabilisation. In wastewater treatment plants, the stability
of foams is often associated with hydrophobic particles such
as bacteria cells (Blackall and Marshall, 1989; Heard et al.,
2008; Petrovski et al., 2010) Particles can show a second
water research 45 (2011) 4355e4366 4357

Author's personal copy
stabilizing mechanism by being surface active themselves and
having a high affinity for the liquideair interface. Eisenreich
et al. (1978) found surface-active proteinaceous matter as
well as small Si, Ca and Fe particles to be responsible for foam
stability.
Addition of salt is another factor promoting foam stability.
Craig et al. (1993) found that bubble coalescence was inhibited
by some salts, whereas others had no effect. According to
Holmberg et al. (2003) salt increases the surfactant critical
packing parameter (CPP), which indicates how close surfac-
tants are packed together at the air-water surface. Thus an
increase in CPP will result in closely packed surfactants, in an
increased surface elasticity and viscosity and thus lead to high
foaming ability and foam stability. Henry (2010) argued that
electrolytes inhibit bubble coalescence in water, but the
inhibition is ion specific. Her experiments on thin film
drainage in electrolyte solutions showed that electrolytes
affect both film drainage rate and film rupture thickness.
According to her results, electrolyte coalescence inhibition is
a nonequilibrium effect that acts upon the dynamic film
drainage process, through ion specific interfacial partitioning.
Pugh (1996) describes the increase of foam stability due to
a mixture of surfactants, e.g. a mixture of tannin and hepta-
noic acid in aqueous solution, whereas much lower foam
stability is observed from the two constituents separately.
In summary, bubble coalescence is the result of bubble
approach, film drainage and finally film rupture. Foam
stability can be increased by adding various substances, such
as particles, salts or a mixture of surfactants.
3. Methods to quantify foam formation
Literature on foam formation and stability mainly originates
from the wastewater sector and in sectors dealing with foams
in industry (Blackall et al., 1991; Blackall and Marshall, 1989;
Heard et al., 2008; Hladikova et al., 2002; Paris, 2004;
Vikingstad et al., 2005). Table 1 provides an overview of
several methods used to measure foam.
In the wastewater sector, tests on foam stability are related
to the occurrence of bulking sludge. The most cited method
was developed by Blackall and Marshall (1989). They designed
a foaming apparatus consisting of a glass cylinder and a sin-
tered glass disc with a maximum pore size of 40e90 mm. In the
cylinder 50 ml of sample are aerated with compressed air
(200 ml/min) via the glass disc. Foam generation and stability
are recorded and assessed according to a classification system
rated in terms of foam volume, bubble size, speed of formation
and time taken for the foam to collapse after aeration ceased.
Heard et al. (2008) slightly modified the method of Blackall
and Marshall (1989) and applied 20 ml of sample which is
aerated with an air flow rate of 100 ml/min. They use the time
at which bubbles collapse as a measure of foam stability.
The AlkaeSeltzer test was developed by Ho und Jenkins
and modified by Kopplow und Barjenbruch (Paris, 2004). This
test uses two tablets of AlkaeSeltzer (AlkaeSeltzer

classic,
Bayer, is a drug containing sodium bicarbonate amongst
others) which are added to a beaker with 250 ml of sample.
Dissolution of the tablets creates bubbles that lead to foam
formation. Size and stability of the bubbles are noted and the
height of foam is measured at intervals of one, three and 5 min
after complete dissolution of the tablet, in order to calculate
the “foam value” (Kopplow and Barjenbruch, 2002).
The scum index (SI) is a method to estimate foaming
severity and was primarily proposed by Pretorius and
Laubscher (1987) and modified by Hladikova et al. (2002). The
first step is the determination of the concentration of sus-
pended solids in the mixed liquor. Then two litres of mixed
liqor are aerated in a laboratory cylinder with a flow rate of
480 ml/min via a sintered silica sand diffusor. After an aera-
tion time of 4 h, the dry mass of recovered scum is deter-
mined. The scum index is calculated by dividing the mass of
suspended solids initially present by the mass of the stored
scum, multiplied by 100%.
Vikingstad et al. (2005) applied foam tests to assess foam
stability in the oil-water-interface. Foam tests were made by
mixing air into the surfactant solution. Air was dispersed into
the 300 ml test solution with a pedal connected to a mixer at
a speed of 2000 rounds per minute for 5 min. The mixer was
a polymix obtained from Kinematica, type RW20 S12. In all the
experiments the height of the foam column above the liquid
phase was measured as a function of time after mixing
ceased.
Limited information exists on the foaming capacity of
effluent from wastewater treatment plants. Madrange et al.
(1992) proposed a method to determine the foaming capacity
of industrial effluents. 250 ml of sample were handshaken for
5 min and the height of the resulting foam was measured with
an accuracy of 0.2 cm. Foam stability, defined as the time until
the foam cover breaks, was measured.
Ruzicka et al. (2009) introduced the foaming factor and the
foam potential to estimate the capability of an effluent to
cause foam in the receiving river. The foaming factor is
derived by shaking 250 ml of effluent in Erlenmeyer flasks
with baffles on a laboratory Shaker (Type Ceromat-U) for
3 min at a speed of 300 rpm. Samples are diluted with dilution
media (in this case unpolluted river water), until no more
foam appears. The dilution factor, at which minimal foam
occurred, is defined as the “foaming factor”. For the calcula-
tion of the “foam potential”, the foaming factor of an effluent
is multiplied with the discharge of the effluent. The calculated
foam potential of an effluent is defined as the volume of river
Table 1 eOverview on methods to measure foam.
Method Measured parameters Cited in
Aeration Foam generation,
Foam stability
Blackall and
Marshall (1989)
Alka-Seltzer Bubble size and
stability,
foam height
Paris (2004)
Aeration Scum index Hladikova et al. (2002)
Mixing Height of foam
column as function
of time
Vikingstad et al. (2006)
Handshaking Foam height, foam
stability
Madrange et al. (1992)
Shaking Foaming factor Ruzicka et al. (2009)
Webcam Foam index Ruzicka et al. (2009)
water research 45 (2011) 4355e43664358

Author's personal copy
water which can potentially become foamed by the effluent’s
discharge, if laboratory conditions are applied.
The study of Ruzicka et al. (2009) also developed a seven-
stage “foam index” (FI) based on webcam pictures of a river
weir, where foam occurred. This parameter was developed to
characterise instream foam formation and assess the amount
of foam on the surface of the river. The index does not
quantify the foam, but allows a semi-quantitative differenti-
ation between the varying foaming conditions. Ruzicka et al.
(2009) successfully correlate the resulting “foam index” in
the river to the emitted “foam potential” of the major point
sources in the catchment.
As a result, all methods to quantify foam (apart from the
foam index) are strongly dependent on the introduction of
a gas source into the liquid, which is provided by (i) aerating,
(ii) mixing or (iii) shaking the sample. As most of the methods
originate from the wastewater sector as a result of the bulking
sludge problems, a uniform approach would be beneficial and
should be developed to make future investigations
comparable.
4. Legal aspects of foam formation
The need to act against degradation of aquatic ecosystems has
been acknowledged by politicians and legislation has been
adopted to stop further deterioration and to restore aquatic
ecosystems to a healthy state (Carstensen, 2007). Examples of
legislation in Europe are the European Water Framework
Directive and the Regulation for Water Pollution Control in
Switzerland; in the USA the US Clean Water Act is the leading
standard. In all these legislations the regulation of foam is an
almost neglected topic.
4.1. Regulation of instream foam formation
The Clean Water Act (CWA) establishes the basic structure for
regulating discharges of pollutants into the waters of the
United States and regulates quality standards for surface
waters. It proclaims that “all surface waters should be free of
scum in unsightly amounts”. The phrase “unsightly” is not
defined any further and its interpretation is subject to the
evaluator (Federal Water Pollution Control Act, 2002).
In the European Union the European Water Framework
Directive (EU WFD) provides the legal standard. It applies the
definition of ‘‘good chemical and ecological status” for river
water bodies, which means only a minor deviation from the
reference (natural) status. The chemical status is regulated by
environmental quality standards for priority substances,
which contain also foam related parameters such as tensides
(e.g. nonylphenols). Thus an indirect criterion for foam exists
by the regulation of tensioactive compounds, although
specific regulation on formation of foam in surface waters is
not available (Water Framework Directive, 2000760/EC, 2000).
The Austrian state monitoring network is administered
according to the requirements of the EU WFD and so far does
not include any monitoring of foam formation
(Bundesministerium fu
¨r Land- und Forstwirtschaft, 2006).
The Regulation for Water Pollution Control in Switzerland
states that “treated wastewater discharge must not lead to
foam formation after advanced mixing in the river with
exception from rainfalls”. The evaluation of instream foam
formation adopts a three-step scale, i.e. “no foam”, “minor to
medium foam” and “lots of foam”. It is a visual survey and the
resulting rating is based on comparison with pictures
(Gewa
¨sserschutzverordnung Schweiz, 1998).
4.2. Regulation of foam emitted by point sources
In terms of point source pollution, the regulation of foam is
weaker than with regards to instream foam formation. In the
CWA, regulation of foam from point sources is not available
(Federal Water Pollution Control Act, 2002). In the EU, the
emissions from municipal wastewater treatment plants are
regulated in the Urban Wastewater Treatment Directive, and
this does not include any parameters regarding foam (Council
Directive 91/271/EEC concerning urban wastewater treatment,
1991). In Austria, the Directive on emissions from municipal
wastewater treatment plants lacks regulation on foam emis-
sions, although emission criteria for foam related parameters
such as tensioactive compounds, e.g. the sum parameter for
anionic and non-ionic surfactants exist (Bundesministerium
fu
¨r Land- und Forstwirtschaft, 1991). Another directive indi-
rectly dealing with foam is the Directive on emissions from
tanneries, which includes the parameter “surface tension” in
the effluent to avoid foam formation in the river
(Bundesministerium fu
¨r Land- und Forstwirtschaft, 2007). The
Swiss Regulation for Water Pollution Control has no emission
based legislation for foam, but does include the assessment of
instream foam formation below point sources
(Gewa
¨sserschutzverordnung Schweiz, 1998).
In summary, the regulation of foam in the aquatic envi-
ronment has been neglected entirely, although the occurrence
of foam is often prominent in the media and is frequently
cited as a reason for public concern. In consequence, proper
legislation is necessary for instream foam formation as well as
for foam originating from point sources. In this context, the
regulation of a sum parameter representing foam formation
such as surface tension or foam potential would offer the
greatest feasibility.
5. Foam formation in wastewater systems
As foam on surface waters is often linked to point source
emissions (Defrain and Schulze-Rettmer, 1989; Madrange
et al., 1992; Ruzicka et al., 2009) and a considerable amount of
literature exists on this subject, foam formation in waste-
water systems is discussed in this section. The formation of
stable foam which reduces oxygen transfer, decreases the
quality of the effluent and therefore increases maintenance
costs, is a widely observed phenomenon in wastewater
treatment plants and was first noted in 1969 (Heard et al.,
2008). It is a common feature of activated sludge systems
around the world and considerable effort has been directed
to enhance understanding of the microbial ecology of
foaming (Petrovski et al., 2010). Microscopic examination of
foams has identified a wide range of bacteria, with the fila-
mentous bacteria Microthrix parvicella and actinomycetes
among the most common (Blackall et al., 1991; Heard et al.,
water research 45 (2011) 4355e4366 4359

Author's personal copy
2008). The results of Lemmer et al. (2005) highlighted that
bacteria assembled in foam comprise morphotypes beside
Microthrix parvicella and nocardioform actinomycetes, which
belong to a variety of species, genera and bacteria groups.
Lemmer et al. (2005) argues that the immense number of
species prevent the recommendation of specific trouble-
shooting measures.
Heard et al. (2008) indicated that bacteria can enhance the
persistence of foams, but cannot in themselves cause foaming
in the absence of a surfactant. Their findings are of impor-
tance, as much of the current literature suggests that foaming
in wastewater treatment plants is caused directly by the
presence of bacteria (Heard et al., 2008). Nonetheless, the
earlier investigations of Blackall and Marshall (1989) high-
lighted that both surfactants and cells were necessary for
stable foam formation, since only unstable foams were
formed in the absence of bacteria, and no foams were formed
in the absence of a surfactant. Interestingly, the surfactant
needed to initialize foam formation must not be a synthetic
surfactant from the influent of the treatment plants, but may
be a biotenside, e.g. glycolipids produced by various sludge
bacteria such as actinomycetes, Pseudomonas or Acineto-
bacter species (Lemmer et al., 2005).
Foam stability seems to be dependent on a large biomass of
filamentous, hydrophobic organisms such as Microthrix parvi-
cella or actinomycetes (Blackall et al., 1991; Blackall and
Marshall, 1989; Heard et al., 2008; Lemmer et al., 2005).
According to Petrovski et al. (2010) foam is generated by
a selective enrichment of these hydrophobic bacteria by
a process of flotation, that requires three components: (i) gas
bubbles surrounded by liquid films, generated by the aeration
system, (ii) surfactants which reduce the surface tensions and
thus prevent liquid drainage from gas bubble walls and (iii)
small hydrophobic particles (bacterial cells) responsible for
the long-term stabilisation. With insufficient hydrophobic
cells, but in the presence of the other two, large amounts of
unstable foam will be generated. These findings strongly
support the investigations of Blackall and Marshall (1989).
Furthermore, the authors demonstrated that the non-
hydrophobic Bacillus subtilis might be an important contrib-
utor to stable foams due to the production of the powerful
surfactant surfactin, supporting the biotenside theory of
Lemmer et al. (2005).
In the experiments of Blackall and Marshall (1989) the
prevention of stable foams has been achieved by the addition
of colloidal, hydrophilic clay particles. Although a variety of
hydrophilic materials was tested, only a 2:1 lattice clay,
montmorillonite, was able to inhibit stable foams. The
authors postulate that a salt-dependent, reversible bacter-
iaemontmorillonite complex is formed, which confers
hydrophilicity to the otherwise hydrophobic actinomycetes.
This property prevents cells from entering and stabilising the
foam phase. Other measures to fight stable foams include
spraying with water to destroy the foam (Lemmer et al., 2005)
or dosing with chemical agents such as polymers (Hwang and
Tanaka, 1998).
In conclusion, the widely observed appearance of stable
foams on wastewater treatment plants results from the
occurrence of surfactants or biotensides in the mixed liquor,
whereas the hydrophobic bacterial cells are responsible for
the long-term stabilisation. Because of the high diversity of
filamentous bacteria the effective control of foam in waste-
water treatment plants is hard to achieve.
6. Relevance of foam on surface waters
6.1. Enrichment of foams in lakes and rivers
Foams occurring on rivers, lakes and in the sea are basically
collections of materials normally present in the SML
(Napolitano and Richmond, 1995). Similar to the foam frac-
tionation techniques used in industry or in wastewater
treatment, the formation of foam on surface waters induces
the transfer and concentration of surface-active substances
from the SML into the foam (Johnson et al., 1989). Depending
on the type of aquatic environment various components are
enriched in the resulting foam. Fisenko (2004) hypothesized
that nature “uses” this “foam fractionation and flotation
technique” as a process for self-purification. In his study he
demonstrated the self-restoration of the Etobicoke river after
a toxic waste spill. Within three months the river was self-
purified which he attributed to the production of large
amounts of foam enriched in substances degrading water
quality, such as cyanide and heavy metals.
Some information is available regarding the enrichment of
certain substances in foams of various rivers and lakes. The
existing information deals with the accumulation of nutri-
ents, lipids, heavy metals, hydrocarbon and pesticides in
“freshwater foam” (Baier et al., 1974; Eisenreich et al., 1978;
Johnson et al., 1989; Napolitano and Richmond, 1995; Parker
and Barsom, 1970; Pojasek and Zajicek, 1978). The enrich-
ment is calculated via the fractionation or enrichment ratio,
which is defined as the concentration of a parameter in the
foam divided by its concentration in the underlying water.
6.1.1. Metals
The analysis of wind-generated lake foam (Lake Mendota,
Wisconsin) highlighted an enrichment with metals as
compared to the underlying water (Eisenreich et al., 1978).
Table 2 provides an overview on the fractionation ratios for
several metals (total) in Lake Mendota compared to other
studies cited in Eisenreich et al. (1978) as well as a study for
foam below the Niagara Falls (Johnson et al., 1989). Although
the fractionation ratios show huge variations, an enrichment
of the foam with metals is obvious. Differences in metal
fractionation ratios between various studies are most likely to
result from the use of different collection techniques and bulk
water concentrations than foam accumulation mechanisms
(Eisenreich et al., 1978). The observed metal enrichment in
foam of Lake Mendota is caused by metal scavenging by
surface-active or particulate material in surface films, bubble
adsorption and atmospheric deposition. Furthermore,
a significant portion of the dissolved metal was complexed by
organic matter or associated with colloidal material accumu-
lated in the foam (Eisenreich et al., 1978).
Pojasek and Zajicek (1978) analysed the metal carrying
capacity of natural SMLs and foams of several streams using
iron and manganese as indicator metals (both dissolved).
They found fractionation ratios varying between 10 and 40 for
water research 45 (2011) 4355e43664360

Author's personal copy
manganese and 30 to 74 for iron depending on the pre-
analyses treatment applied. Half of the metals were strongly
bound to organic terrestrial decomposition products; the rest
were present as inorganic species or weakly bound organic
complexes.
6.1.2. Carbon and nutrients
Parker and Barsom (1970) investigated the SML of three
freshwater habitats in the vicinity of St. Louis. Total nitrogen
and orthophosphate showed a two- to threefold concentra-
tion in the SML compared to the underlying water. Unfortu-
nately, no absolute numbers are available for this study.
In Niagara Falls the fractionation ratio for DOC is about 8
(Johnson et al., 1989) compared to an average ratio of 40 for
DOC and 48 for TOC in the foam of Lake Mendota (Eisenreich
et al., 1978). The ratio for organic nitrogen was 95 in Lake
Mendota, indicating the presence of large quantities of
proteinaceous matter. About 80% of the total phosphorus
occurred in dissolved form and was evenly distributed
between dissolved reactive phosphorus (DRP) and dissolved
organic phosphorus (DOP) with average ratios of 11 and 84,
respectively (Eisenreich et al., 1978).
6.1.3. Lipids and hydrocarbons
Lipids are one of the major organic constituents of SMLs and
foams because of their hydrophobicity, a low relative density
and low vapour pressure (Napolitano and Cicerone, 1999). The
lipid concentrations of foam samples from rivers in eastern
Tennessee show some variation, but were higher than in the
underlying water with fractionation ratios spanning two
orders of magnitude. According to the authors, the varying
concentrations between the streams could be attributed to
differences in the particle load of the foam, foam age and the
extent of colonization by microbes (Napolitano and
Richmond, 1995). Fractionation ratios of foam below the
Niagara falls ranged from 15 for total fatty acids to 370 for total
sterol depending on the degree of polarity (Johnson et al.,
1989).
Napolitano and Richmond (1995) regenerated foam in the
laboratory to measure the enrichment under controlled
conditions (8l of stream water plus 200 ml of corresponding
foam). The resulting fractionation ratios for phospholipids
and hydrocarbons were much lower than those found in the
field. These findings suggest that high concentrations of lipids
in natural foams are not a direct consequence of the foam
formation, but indicate a secondary enrichment of lipids in
the foam after its formation due to microbial growth or
entrapment of suspended solids.
Natural hydrocarbons typically account for only a small
proportion of the total lipids (typically <5%). The presence of
hydrocarbons at 20%e30% in river foams in eastern Tennes-
see and at 10%e15% in foam below the Niagara Falls indicates
oil contamination (Johnson et al., 1989; Napolitano and
Richmond, 1995).
Eisenreich et al. (1978) reported high concentrations of
chlorinated hydrocarbons, such as dieldrin and DDT-group
pesticides (4e360 ng/l) in foam of Lake Mendota compared to
the underlying water (<1 ng/l). Total DDT (sum of DDT, DDE,
DDD) in the foam ranged from 75 to 767 ng/l. Although the
resulting fractionation ratios are significantly high, they are
subject to some uncertainty due to very low levels in the
underlying water.
6.1.4. Polychlorinated biphenyl (PCB)
Polychlorinated biphenyls are a class of organic compounds
with 1e10 chlorine atoms attached to biphenyl, which is
a molecule composed of two benzene rings. Due to PCB’s
toxicity and classification as a persistent organic pollutant,
PCB production was banned by the Stockholm Convention on
Persistent Organic Pollutants in 2001. In Lake Mendota the
PCBs were detected in the foam samples with fractionation
ratios in the range of 100e1000, which is far higher than in the
river foam in eastern Tennessee with ratios between 5 and 9
(Eisenreich et al., 1978; Napolitano and Richmond, 1995).
In summary, various substances enriched in the SML will
be transferred into and concentrated in the foam. The pres-
ence of a substance in foam does not necessarily mean that it
causes foam. Often substances, e.g. metals are complexed and
concentrated in the foam, even though other surface-active
compounds are responsible for the foam formation. The
effect of the enriched substances on the aquatic environment
will be discussed in section 6.3.
6.2. Occurrence and composition of sea foam
The occurrence of sea foam is a widely known phenomenon
around the world (Ba
¨tje and Michealis, 1986; Craig et al.,
1989; Eberlein et al., 1985; Kesaulya et al., 2008; Seuront
et al., 2006). According to Baier et al. (1974) stable sea
foams usually include a major silica component, which can
be associated with diatom remnants. Ba
¨tje and Michaelis
(1986) report unusual amounts of sea foam in the North
Sea in 1978 caused by a bloom of the planktonic algae
Phaeocystis pouchetii. During mass production of this
organism the water turns reddish-brown and great amounts
of carbohydrates and proteins are released by the
Table 2 eFractionation ratios for heavy metals in “freshwater foams” emodified from Eisenreich et al. (1978)
Metal (total) Fractionation ratio (average)
Lake Mendota Delaware Bay Lake Michigan Niagara Falls
Eisenreich et al., 1978 Szekielda et al., 1972 Elzerman, 1976 Johnson et al., 1989
Zn 293 w10,000 14 80
Cd 544 67 20
Pb 1110 w10,000 271
Cu 448 w10,000 98 300
Fe 240
water research 45 (2011) 4355e4366 4361

Author's personal copy
mucilaginous cell colonies at the peak of the bloom and
during the breakdown. Through wave action this solution is
whisked and washed ashore, where layers of foam cover the
beaches up to several meters. In Guzma
´n et al. (1990)
a severe bloom of Cochlodinium catenatum in the eastern
Pacific is reported to be responsible for copious amounts of
viscous foams and mucus in the water column.
According to Velimirov (1980) many seaweeds exude
water-soluble mucilage, which provides enough surface-
active agents to induce foam formation. A further important
contributor to foam formation are broken phytoplankton
cells, which release organic matter causing foam. Velimirov’s
(1980) analysis of sea foam collected near kelp beds at
Oudekraal (South Africa) demonstrated that total protein was
the dominant component (21% of the total freeze-dried
weight), followed by total lipids (6.1%) and carbohydrates
(2.4%). Within the protein fraction the trichloroacetic-acid
(TCA)-precipitated protein was the most common (15%),
which is an easily metabolizable protein available for
consumers (Velimirov, 1980). In a further study, Velimirov
(1982) investigated the amount of individual sugar and lipid
components in foam near kelp beds. The results indicate
a dominance of aldoses and deoxy sugars with b-mannose
(32% of total carbohydrates) being the prevalent component
followed by b-glucose (19%) and b-galactose (16%). The most
important lipid class is represented by triglycerides, which
amount to more than 50% of total lipids. Amongst the
remaining lipid classes the free fatty acids (22%) and polar
lipids (7%) seem worth mentioning. In contrast to foams from
rivers and streams the hydrocarbons were only present in
trace concentrations or totally absent from foam.
Sea foam collected at two sites in New Brunswick was
studied by Ba
¨rlocher et al. (1988). The authors found phenols
to be the major constituent, whereas approximately 13% of
the organic carbon content was present in amino acids and
carbohydrates. Protein concentration was two to four times
higher than that of carbohydrates. Up to 75% of the organic
carbon content remained unidentified and could partly be
accounted for by lipids. Subsequent investigations by Craig
et al. (1989) showed a strong correlation between organic
carbon in the sea foam and phenolics. As phenolics are more
common in higher plants than in marine algae, the authors
argue that vascular plants detritus is the dominant source of
the observed sea foam. Their results confirm findings from an
earlier study by Coffey (1986), who determined stable C
isotope ratios of sea foam and concluded that local Spartina
marshes and terrestrial plants are the major contributors of
sea foam carbon.
In summary, sea foam results mainly from the enrichment
of surface-active substances exuded by (i) phytoplankton
blooms, (ii) seaweed or (iii) even terrestrial plants in the SML.
The enriched material is whisked into foam by the action of
waves and washed ashore, where unaestethic foam layers
accumulate.
6.3. Ecological importance of foam
Due to its composition and capacity to accumulate various
components, the literature suggests foam has an ecological
relevance.
6.3.1. Toxicity of foam
SMLs and foams are subject to concentrations of materials
transported by bubbles. Dissolved and particulate materials
adsorbed on a bubble surface are forced into intimate contact
as the bubble rises resulting in surface coagulation. This
process provides a mechanism for the conversion of dissolved
and colloidal materials into particulate form and can produce
aggregates rich in surface-active toxins. Foams enriched with
those surface-active aggregates represent regions in which
organisms experience accelerated rates of accumulated toxic
material (Johnson et al., 1989). According to Napolitano and
Richmond (1995) various pollutants might be concentrated
in the SML. As a consequence, the neustonic organisms (rep-
resenting the biocoenosis of the SML) could be exposed to far
higher concentrations of contaminants in the SML and the
resulting foam than those in underlying waters.
Sea foam collected in New Brunswick was shown to have
a toxic effect on the amphipod Corophium volutator (macro-
invertebrate) which was attributed to either the phenolic
content of the foam or the levels of heavy metals and pesti-
cides (Craig et al., 1989). Eberlein et al. (1985) report that sea
foam produced by a Phaeocystis pouchetii bloom contained
acrylic acid which is known to be an antibiotic. Guzma
´n et al.
(1990) highlight the suffocation of scleractinian corals by
mucilagic substances causing sea foam in the eastern Pacific
during a bloom of dinoflagellates. Their results indicate that
the production of the polysaccharides may be an indirect
mechanism of mortality. Harmful effects caused by an
external coating of marine birds with a proteinaceous foam
derived from a red tide bloom is reported by Jessup et al.
(2009). Although this red tide bloom was ostensibly non-
toxic, the seabird feathers dipped in the foam lost their
normal water repellence and became soaked resulting in
feather fouling, reduced mobility and hypothermia.
The breaking of foam bubbles carrying surface-active
pollutants produce aerosols, which become widely distrib-
uted and may cause an increased risk of human exposure to
toxins and pathogens (Johnson et al., 1989; Maynard, 1968).
Eisenreich et al. (1978) suggested that foam was both a sink for
inorganic and organic material and a source of chemical input
to the atmosphere by bubble breaking and wind-suspension
processes. Furthermore the authors highlighted the crucial
role of foam in the transfer of toxic pollutants into the food
web, as bacteria and plankton abundant in the foam are
ingested by fish and waterfowl are commonly observed to feed
on foam.
Finally, the enrichment of metals, such as Zn, Pb, Cu, Fe,
Mn and chlorinated hydrocarbons can cause an environ-
mental problem, if these foams are transported to drinking
water supplies (Harden and Williams, 1989).
6.3.2. Foam as food resource
The enrichment of foam with various substances is not only
a threat to the aquatic biocoenosis, but also represents
a potential food resource for organisms either living in the sea
or at the shoreline (Ba
¨rlocher et al., 1988; Craig et al., 1989;
Velimirov, 1980, 1982).
The calorific content for freshly formed marine foam near
Kelp beds is reported to be 15 kJ/g ash-free dry weight, which
water research 45 (2011) 4355e43664362

Author's personal copy
demonstrates the importance of foam as potential energy
source for the marine environment Velimirov (1980). Accord-
ing to the author the mucilage excreted by the kelp provides
enough surface-active agents to induce foam formation and to
improve the foam stability. Long lasting foams are a prereq-
uisite for sufficient movement of the foam to various sites in
and around the kelp beds, enabling the energy pool to be
available to the consumer chain. Although mucilage consist-
ing mainly of the sugar mannitol, which is likely to be an
important component of the foam, none of the foam samples
investigated by Velimirov (1982) contained quantifiable
amounts of this sugar type. One explanation for the lack of
mannitol could be the presence of heterotrophic organisms in
the foam, which rapidly utilize the released sugar.
Ba
¨rlocher et al. (1988) and Craig et al. (1989) investigated
the capacity of sea foam to serve as a food source for the
amphipod Corophium volutator. In laboratory experiments they
proved that C. volutator has a wide variety of enzymes to digest
sea foam. The released sugars and amino acids could poten-
tially satisfy 70% of the nutritional requirements of the
amphipod. However, the large spectrum of fatty acids in foam
samples, suggest that sea foam concentrates and distributes
essential dietary components which most consumers are
unable to synthesize (Velimirov, 1982).
River foam collected from five western North American
rivers contained the Bradford-reactive soil protein (BRSP),
a glycoprotein of soil and of arbuscular mycorrhizal fungal
origin, which was also present in alluvial soils (Harner et al.,
2004). Laboratory experiments proved that the protein can
be leached and washed from the soil and accumulate in the
foam due to its hydrophobic properties. The authors speculate
that BRSP might act as a nutrient source for aquatic food webs
by contributing carbon and nitrogen from terrestrial sources
to water via erosion and leaching of floodplain soils contain-
ing the protein.
6.3.3. Foam as habitat
Foam is not only a food resource for organisms, but also acts
as an important habitat for various species. Regardless of their
source, coastal bio foams have been described as enclosing
marine metazoan fauna of several taxa and larvae, e.g. poly-
chaete, mussel and crustacean (Castilla et al., 2007). Eberlein
et al. (1985) reported massive occurrences of saprophytic
bacteria on sea foam collected in the German Bight. Wilson
(1959) demonstrated that sea foam contained 25% solid
matter, much of which consisted of bacteria and diatoms.
Velimirov (1980) found high densities of bacteria in foam with
significantly higher bacterial densities in old foam than in
fresh foam.
Relatively large amounts of phospholipids measured in
river foams indicate that bacteria, protozoa and/or algae are
major contributors to organic matter in foams (Napolitano
and Richmond, 1995).
In studies dealing with aquatic hyphomycetes, also known
as amphibious fungi, foam samples show that hyphomycetes’
spores are stored in foams in a viable, ungerminated state for
considerable periods of time (Harrington, 1997; Pascoal et al.,
2005).
The most comprehensive investigation on foam as habitat
was a study by Maynard (1968) who collected foam from
various aquatic habitats (freshwater and marine) and found
heavy concentrations of diatoms, lesser numbers of dinofla-
gellates and green and blue-green algae. An outstanding fact
derived from her study was that the majority of species
present in foam was either benthic (attached to sediments) or
periphytic (attached to plants eaufwuchs) rather than
planktonic (free floating in the water column). She considered
foam to be an important habitat which has been ignored
previously.
6.3.4. Other roles of foam in the environment
Ettema et al. (1989) discussed the role of foam in the initiation
of ice covers. The observations reported indicate that small
and medium rivers convey chemicals resulting either from the
decay of organic substances or from manmade pollution that
generates foam. The resulting foam possibly causes ice covers
to form more rapidly than in streams without foam formation
and at water temperatures above freezing temperature. This
is particularly likely in small rivers where complete ice-cover
reduces air supply resulting in decreasing oxygen concentra-
tions. However, the importance of foam as an ice-cover initi-
ation mechanism diminishes with increasing size and width
of a river, as wind fetch increases leading to foam dispersal.
Apart from the physical effects, foam is known to ensure
egg retention and larval development in organisms (Castilla
et al., 2007). According to the authors, foam nests enhance
the fertilization success and the retention of eggs and larvae
in freshwater nest-building fish, tropical aquatic frogs and
tunicates.
In summary, the formation of foam either in freshwater
systems or as sea foam is not imperatively disadvantageous
for the environment. Although foams may show toxic effects
depending on the substances enriched within, they also can
serve as a food resource and as a habitat for organisms.
7. Conclusions
This review on foam in the aquatic environment has high-
lighted that minor amounts of information are available in
literature, and that most studies dealing with that subject are
at least twenty to thirty years old.
Several significant references on surface microlayers (SML)
in freshwater and marine ecosystems were identified. SML
represent the air-water boundary where surface-active
components accumulate. As a consequence of the SML, the
introduction of air and other gases into the water by turbu-
lences, cascades etc. will lead to foam formation. In the
presence of organic (living or dead organisms) and inorganic
(silt, sand) particles very stable foams can occur.
Foam formation is observed in nearly every aquatic envi-
ronment, such as rivers, lakes and oceans. Although the
majority of studies show that foam is the product of natural
processes and factors, the public tends to associate foam
formation with manmade pollution. Public concern is likely to
be enhanced due to the visibility of foam, which lead to it
being more obvious than “hidden” chemical pollution.
Surface-active components causing foam include the
degradation products of organic material (e.g. humic
substances), lipids and proteins originating from aquatic
water research 45 (2011) 4355e4366 4363

Author's personal copy
plants or the terrestrial environment, and exudation or
decomposition products of phytoplankton. Manmade foam is
often the result of point source pollution (particularly from
industry) or diffuse pollution originating mainly from
agriculture.
There is no regulation regarding instream foam formation
in the United States, nor the EU or Switzerland. Although
emissions from point sources are strictly governed in general,
the foam causing potential of point sources is not regulated.
Methods to assess foaming and foam stability are found
mainly in the wastewater sector. In wastewater treatment
plants stable foam is mainly observed as a result of filamen-
tous bacteria such as Microthrix parvicella or nocardioform
actinomycetes which occur in the water. The role of the
bacteria in foam formation is on the one hand the production
of surface-active biotensides, and on the other hand the sta-
bilisation of foam due to their hydrophobicity.
Apart from the aesthetic aspects of foam, foam formation
involves several other ecological aspects. Due to its enrich-
ment capacity, carbon, nutrients, metals, hydrocarbons and
even pesticides accumulate in foam. According to Napolitano
and Richmond (1995) foams are relatively isolated microen-
vironments, in which the inhabiting organisms are exposed to
higher concentrations of contaminants. Toxic effects of foam
were demonstrated for the amphipod Corophium volutator and
the transfer of toxic substances from foam into organisms via
the food web seems to be a potential danger. The break of
foam bubbles carrying surface-active pollutants may even
cause an increased risk of human exposure to toxins and
pathogens.
Foam is also believed to be an important food resource and
a site of nutrient recycling which transfers energy to the
consumer level. Some literature is available on the impor-
tance of foam as a habitat, especially for benthic and peri-
phytic organisms.
The review of the existing literature demonstrated both the
crucial role of foam with regards to pollution and the ecolog-
ical aspects of foam in the aquatic environment. Considering
this, it is even more surprising that information on foam in the
aquatic environment is still scarce and that this topic appears
to have been ignored over the last decade.
Acknowledgement
The authors would like to thank the Austrian Science Funds
FWF for financial support as part of the Doctoral program DK-
plus W1219-N22 on Water Resource Systems.
references
Baier, R.E., Goupil, D.W., Perlmutter, S., King, R., 1974. Dominant
chemical composition of sea-surface films, natural slicks and
foams. Journal de Recherches Atmospheriques 8, 571e600.
Ba
¨rlocher, F., Gordon, J., Ireland, R.J., 1988. Organic composition of
seafoam and its digestion by Corophium volutator (Pallas).
Journal of Experimental Marine Biology and Ecology 115,
179e186.
Ba
¨tje, M., Michealis, H., 1986. Phaeocystis pouchetii blooms in the
East Frisian coastal waters (German Bight, North Sea). Marine
Biology 93, 21e27.
Binks, B.P., 2002. Particles as surfactantsesimilarities and
differences. Current Opinion in Colloid & Interface Science 7,
21e41.
Blackall, L.L., Harbers, A.E., Greenfield, P.F., Hayward, A.C., 1991.
Activated sludge foams: effects of environmental variables on
organism growth and foam formation. Environmental
Technology 12, 241e248.
Blackall, L.L., Marshall, K.C., 1989. The mechanism of stabilization
of actinomycete foams and the prevention of foaming under
laboratory conditions. Journal of Industrial Microbiology &
Biotechnology 4, 181e187.
Bundesministerium fu
¨r Land- und Forstwirtschaft, U.u.W, 1991.
Allgemeine Abwasseremissionsverordnung Republik
O
¨sterreich.
Bundesministerium fu
¨r Land- und Forstwirtschaft, U.u.W, 2006.
In: O
¨sterreich, R. (Ed.), 479. Verordnung -
Gewa
¨sserzustandsu
¨berwachungsverordnung GZU
¨V.
Bundesministerium fu
¨r Land- und Forstwirtschaft, U.u.W, 2007.
61. Verordnung - A
¨nderung der AEV Gerberei, 3 pp.
Buzzacchi, M., Schmiedel, P., von Rybinski, W., 2006. Dynamic
surface tension of surfactant systems and its relation to foam
formation and liquid film drainage on solid surfaces. Colloids
and Surfaces A: Physicochemical and Engineering Aspects 273,
47.
Carstensen, J., 2007. Statistical principles for ecological status
classification of water framework directive monitoring data.
Marine Pollution Bulletin 55, 3e15.
Castilla, J.C., Manriquez, P.H., Delgado, A.P., Gargallo, L., Leiva, A.,
Radic, D., 2007. Bio-foam enhances larval retention in a free-
spawning marine tunicate. Proceedings of the National
Academy of Sciences of the United States of America 104,
18120e18122.
Coffey, W.L.P., 1986. Organic Matter in Seafoam. Mount Allison
University, Sackville, New Brunswick.
Council Directive 91/271/EEC, 1991. Concerning Urban
Wastewater Treatment. European Council, 16 pp.
Craig, D., Ireland, R.J., Ba
¨rlocher, F., 1989. Seasonal variations in
the organic composition of seafoam. Journal of Experimental
Marine Biology and Ecology 130, 71e80.
Craig, V.S.J., Ninham, B.W., Pashley, R.M., 1993. Effect of
Electrolytes on Bubble Coalescence. Nature Publishing Group,
London (ROYAUME-UNI).
Dale, C., West, C., Eade, J., Rito-Palomares, M., Lyddiatt, A., 1999.
Studies on the physical and compositional changes in
collapsing beer foam. Chemical Engineering Journal 72, 83.
Defrain, M., Schulze-Rettmer, R., 1989. Schaumentwicklung in
biologisch gereinigtem Abwasser und im Gewa
¨sser. Vom
Wasser 73, 251e257.
Desroy, N., Denis, L., 2004. Influence of spring phytodetritus
sedimentation on intertidal macrozoobenthos in the
eastern English Channel. Marine Ecology-Progress Series
270, 41e53.
Eberlein, K., Leal, M.T., Hammer, K.D., Hickel, W., 1985. Dissolved
organic substances during a Phaecystis pouchetii bloom in the
German Bight (North Sea). Marine Biology 89, 311e316.
Eisenreich, S.J., Elzerman, A.W., Armstrong, D.E., 1978.
Enrichment of micronutrients, heavy metals, and chlorinated
hydrocarbons in wind-generated lake foam. Environmental
Science & Technology 12, 413e417.
Elzerman, A.W., 1976. Surface microlayer-microcontaminant
interactions in freshwater lakes. PhD thesis. University of
Wisconsin, Madison, Wis.
Ettema, R., Johnson, J.K., Schaefer, J.A., 1989. Foam-initiated ice
covers on small rivers and streams: an observation. Cold
Regions Science and Technology 16, 95e99.
water research 45 (2011) 4355e43664364

Author's personal copy
Federal Water Pollution Control Act, 2002. In: Congress, U.S. (Ed.),
Senate and House of Representatives of the United States of
America.
Figueredo, R.C.R., Sabadini, E., 2003. Firefighting foam stability: the
effect of the drag reducer poly(ethylene) oxide. Colloids and
Surfaces A: Physicochemical and Engineering Aspects 215, 77.
Fisenko, A.I., 2004. A new long-term on site clean-up approach
applied to non-point sources of pollution. Water, Air, & Soil
Pollution 156, 1.
Gewa
¨sserschutzverordnung Schweiz, 1998. In: Bundesrat, S. (Ed.).
Schweizer Bundesrat.
Guzma
´n, H.M., Corte
´s, J., Glynn, P.W., Richmond, R.H., 1990. Coral
mortality associated with dino-flagellate blooms in the
eastern Pacific (Costa Rica and Panama). Marine Ecology
Progress Series 60, 299e303.
Harden, S., Williams, D., 1989. Stable carbon isotopic evidence for
sources of particulate organic carbon found in sea foam.
Estuaries and Coasts 12, 49e56.
Harner, M.J., Ramsey, P.W., Rillig, M.C., 2004. Protein
accumulation and distribution in floodplain soils and river
foam. Ecology Letters 7, 829e836.
Harrington, T.J., 1997. Aquatic hyphomycetes of 21 rivers in
southern Ireland. Biology and Environment-Proceedings of the
Royal Irish Academy 97B, 139e148.
Heard, J., Harvey, E., Johnson, B.B., Wells, J.D., Angove, M.J., 2008.
The effect of filamentous bacteria on foam production and
stability. Colloids and Surfaces B: Biointerfaces 63, 21e26.
Henry, C.L., 2010. Bubbles, Thin Films and Ion Specificity.
Department of Applied Mathematics, Research School of
Physical Sciences and Engineering. The Australian National
University.
Hladikova, K., Ruzickova, I., Klucova, P., Wanner, J., 2002. An
investtgation into studying of the activated sludge foaming
potential by using physicochemical parameters. Water
Science and Technology 46, 525e528.
Holmberg, K., Jo
¨nsson, B., Kronberg, B., Lindman, B., 2003.
Foaming of Surfactant Solutions. John Wiley & Sons, Ltd.
Ho
¨rtnagl, P., Pe
´rez, M.T., Zeder, M., Sommaruga, R., 2010. The
bacterial community composition of the surface microlayer in
a high mountain lake. FEMS Microbiology Ecology 73, 458e467.
Hwang, Y., Tanaka, T., 1998. Control of Microthrix parvicella
foaming in activated sludge. Water Research 32, 1678e1686.
Jessup, D.A., Miller, M.A., Ryan, J.P., Nevins, H.M., Kerkering, H.A.,
Mekebri, A., Crane, D.B., Johnson, T.A., Kudela, R.M., 2009.
Mass Stranding of marine birds caused by a surfactant-
producing red tide. PLoS ONE 4, e4550.
Johnson, B.D., Zhou, X., Parrish, C.C., Wangersky, P.J., Kerman, B.
R., 1989. Fractionation of particulate matter, the trace metals
Cu, Cd, and Zn, and lipids in foam and water below Niagara
falls. Journal of Great Lakes Research 15, 189e196.
Kesaulya, I., Leterme, S.C., Mitchell, J.G., Seuront, L., 2008. The
impact of turbulence and phytoplankton dynamics on foam
formation, seawater viscosity and chlorophyll concentration
in the eastern English Channel. Oceanologia 50, 167e182.
Kopplow, O., Barjenbruch, M., 2002. Beurteilung und
Weiterentwicklung von Methoden zur Erfassung des
Schaumpotentials. Institut fu
¨r Kulturtechnik und Siedlungs-
wasserwirtschaft, Universita
¨t Rostock.
La
´nsky´, M., Ruzickova
´, I., Bena
´kova
´, A., Wanner, J., 2005. Effect of
Coagulant dosing on phyiscochemical and microbiological
characteristics of activated sludge and foam formation. Acta
Hydrochimica Et Hydrobiologica 33, 266e269.
Lemmer, H., Lind, G., Mu
¨ller, E., Schade, M., 2005. Non-famous
scum bacteria: biological characterization and troubleshooting.
Acta hydrochimica et hydrobiologica 33, 197e202.
Lu, K.H., Jin, C.H., Dong, S.L., Gu, B.H., Bowen, S.H., 2006. Feeding
and control of blue-green algal blooms by tilapia (Oreochromis
niloticus). Hydrobiologia 568, 111e120.
Madrange, L., Chaboury, P., Ferrandon, O., Mazet, M., Rodeaud, J.,
1992. Study of the formation and stability of chemical foam on
the Vienne river between Limoges and Confolens. Revues des
Sciences de L’eau 6, 315e334.
Maynard, N.G., 1968. Aquatic foams as an acological habitat.
Zeitschrift fu
¨r Allgemeine Mikrobiologie 8, 119e126.
Mills, M.S., Thurman, E.M., Ertel, J., Thorn Kevin, A., 1996. Organic
Geochemistry and Sources of Natural Aquatic Foams, Humic
and Fulvic Acids. American Chemical Society. 151e192.
Napolitano, G.E., Cicerone, D.S., 1999. Lipids in water-surface
microlayers and foams. In: Arts, M.T., Wainmann, B.C. (Eds.),
Lipids in Freshwater Ecosystems, pp. 235e262.
Napolitano, G.E., Richmond, J.E., 1995. Enrichment of biogenic
lipids, hydrocarbons and PCBs in stream-surface foams.
Environmental Toxicology and Chemistry 14, 197e201.
Paris, S., 2004. Beka
¨mpfung von Schwimmschlamm verursacht
durch Microthrix parvicella. Lehrstuhl fu
¨r Wassergu
¨te- und
Abfallwirtschaft. Technische Universita
¨tMu
¨nchen, Mu
¨nchen,
138 pp.
Parker, B., Barsom, G., 1970. Biological and chemical significance
of surface microlayers in aquatic ecosystems. BioScience 20,
87e93.
Pascoal, C., Marvanova, L., Cassio, F., 2005. Aquatic hyphomycete
diversity in streams of Northwest Portugal. Fungal Diversity
19, 109e128.
Pedersen, K.H., Andersen, S.I., Jensen, A.D., Dam-Johansen, K.,
2007. Replacement of the foam index test with surface tension
measurements. Cement and Concrete Research 37, 996.
Petrovski, S., Dyson, Z.A., Quill, E.S., McIlroy, S.J., Tillett, D.,
Seviour, R.J., 2010. An examination of the mechanisms for
stable foam formation in activated sludge systems. Water
Research 45, 2146e2154.
Piazza, L., Gigli, J., Bulbarello, A., 2008. Interfacial rheology study
of espresso coffee foam structure and properties. Journal of
Food Engineering 84, 420e429.
Pojasek, R.B., Zajicek, O.T., 1978. Surface microlayers and
foamsesource and metal transport in aquatic systems. Water
Research 12, 7e10.
Poremba, R., 1991. Untersuchung zur Schaumbildung auf
Fließgewa
¨ssern. Fachhochschule fu
¨r Druck, Stuttgart, 59 pp.
Pretorius, W.A., Laubscher, C.J.P., 1987. Control of biological scum
in activated sludge plants by means of selective flotation.
Water Science and Technology 19, 1003e1011.
Pugh, R.J., 1996. Foaming, foam films, antifoaming and
defoaming. Advances in Colloid and Interface Science 64, 67.
Regismond, S.T.A., Winnik, F.M., Goddard, E.D., 1998. Stabilization
of aqueous foams by polymer/surfactant systems: effect of
surfactant chain length. Colloids and Surfaces A:
Physicochemical and Engineering Aspects 141, 165.
Ruzicka, K., Gabriel, O., Bletterie,U.,Winkler,S.,Zessner,M.,
2009. Cause and effect relationship between foam
formation and treated wastewater effluents in
a transboundary river. Physics and Chemistry of the Earth,
Parts A/B/C 34, 565.
Seuront, L., Vincent, D., Mitchell, J.G., 2006. Biologically induced
modification of seawater viscosity in the Eastern English
Channel during a Phaeocystis globosa spring bloom. Journal of
Marine Systems 61, 118.
Shi, H.X., Qu, J.H., Wang, A.M., Li, G.T., Lei, P.J., Liu, H.J., 2005.
Primary investigation of blue-green algae and their toxins
from water blooms in Guanting Reservoir of Beijing. Chemical
Journal of Chinese Universities-Chinese 26, 1653e1655.
Szekielda, K.-H., Kupperman, S.L., Klemas, U., Polis, D.F., 1972.
Elemental enrichment in organic films and foam associated
with aquatic frontal systems. Journal of Geophysical Research
77, 5278e5282.
Tafreshi, A.M., Marzo, M.D., 1999. Foams and gels as fire
protection agents. Fire Safety Journal 33, 295.
water research 45 (2011) 4355e4366 4365

Author's personal copy
Torregrossa, M., Viviani, G., Vinci, V., 2005. Foaming estimation
tests in activated sludge systems. Acta Hydrochimica Et
Hydrobiologica 33, 240e246.
Vanrell, G., Canals, R., Esteruelas, M., Fort, F., Canals, J.M.,
Zamora, F., 2007. Influence of the use of bentonite as a riddling
agent on foam quality and protein fraction of sparkling wines
(Cava). Food Chemistry 104, 148.
Velimirov, B., 1980. Formation and potential trophic significance
of marine foam near kelp beds in the benguela upwelling
system. Marine Biology 58, 311e318.
Velimirov, B., 1982. Sugar and lipid components in Sea foam near
kelp beds. Marine Ecology 3, 97e107.
Vikingstad, A.K., 2006. Static and Dynamic Studies of Foam and
Foam-oil Interactions. Department of Chemistry. University of
Bergen, Bergen, 88 pp.
Vikingstad, A.K., Skauge, A., Høiland, H., Aarra, M., 2005. Foam-oil
interactions analyzed by static foam tests. Colloids and Surfaces
A: Physicochemical and Engineering Aspects 260, 189e198.
Water Framework Directive 2000760/EC, 2000. In: Council, E.
(Ed.), Directive of the European Parliament and of the
Council 2000/60/EC Establishing a Framework for
Community Action in the Field of Water Policy. European
Union, Luxembourg.
Wegner, C., Hamburger, M., 2002. Occurrence of stable foam
in the Upper Rhine River caused by plant-derived
surfactants. Environmental Science & Technology 36,
3250e3256.
Wilson, A.T., 1959. Surface of the ocean as a source of air-borne
nitrogenous material and other plant nutrients. Nature 184,
99e101.
Wilson, M.I., Robertson, L.D., Daly, M., Walton, S.A., 1995. Effects
of visual cues on assessment of water quality. Journal of
Environmental Psychology 15, 53.
Zhang, H., Miller, C.A., Garrett, P.R., Raney, K.H., 2004. Defoaming
effect of calcium soap. Journal of Colloid and Interface Science
279, 539.
water research 45 (2011) 4355e43664366