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An overview of dissolved organic carbon in groundwater and implications for drinking water safety



Dissolved organic carbon (DOC) is composed of a diverse array of compounds, predominantly humic substances, and is a near ubiquitous component of natural groundwater, notwithstanding climatic extremes such as arid and hyper-arid settings. Despite being a frequently measured parameter of groundwater quality, the complexity of DOC composition and reaction behaviour means that links between concentration and human health risk are difficult to quantify and few examples are reported in the literature. Measured concentrations from natural/unpolluted groundwater are typically below 4 mg C/l, whilst concentrations above these levels generally indicate anthropogenic influences and/or contamination issues and can potentially compromise water safety. Treatment processes are effective at reducing DOC concentrations, but refractory humic substance reaction with chlorine during the disinfection process produces suspected carcinogenic disinfectant by-products (DBPs). However, despite engineered artificial recharge systems being commonly used to remove DOC from recycled treated wastewaters, little research has been conducted on the presence of DBPs in potable groundwater systems. In recent years, the capacity to measure the influence of organic matter on colloidal contaminants and its influence on the mobility of pathogenic microorganisms has aided understanding of transport processes in aquifers. Additionally, advances in polymerase chain reaction techniques used for the detection, identification, and quantification of waterborne pathogens, provide a method to confidently investigate the behaviour of DOC and its effect on contaminant transfer in aquifers. This paper provides a summary of DOC occurrence in groundwater bodies and associated issues capable of indirectly affecting human health.
An overview of dissolved organic carbon in groundwater
and implications for drinking water safety
S. Regan
&P. Hynds
&R. Flynn
Received: 16 September 2016 / Accepted: 23 March 2017 /Published online: 22 April 2017
#Springer-Verlag Berlin Heidelberg 2017
Abstract Dissolved organic carbon (DOC) is composed of a
diverse array of compounds, predominantly humic sub-
stances, and is a near ubiquitous component of natural ground-
water, notwithstanding climatic extremes such as arid and
hyper-arid settings. Despite being a frequently measured pa-
rameter of groundwater quality, the complexity of DOC com-
position and reaction behaviour means that links between con-
centration and human health risk are difficult to quantify and
few examples are reported in the literature. Measured concen-
trations from natural/unpolluted groundwater are typically be-
low 4 mg C/l, whilst concentrations above these levels gener-
ally indicate anthropogenic influences and/or contamination
issues and can potentially compromise water safety. Treatment
processes are effective at reducing DOC concentrations, but
refractory humic substance reaction with chlorine during the
disinfection process produces suspected carcinogenic disin-
fectant by-products (DBPs). However, despite engineered ar-
tificial recharge systems being commonly used to remove
DOC from recycled treated wastewaters, little research has
been conducted on the presence of DBPs in potable ground-
water systems. In recent years, the capacity to measure the
influence of organic matter on colloidal contaminants and its
influence on the mobility of pathogenic microorganisms has
aided understanding of transport processes in aquifers.
Additionally, advances in polymerase chain reaction tech-
niques used for the detection, identification, and quantification
of waterborne pathogens, provide a method to confidently
investigate the behaviour of DOC and its effect on contami-
nant transfer in aquifers. This paper provides a summary of
DOC occurrence in groundwater bodies and associated issues
capable of indirectly affecting human health.
Keywords Dissolved organic carbon .Health .Disinfectant
by-products .Microbial processes .Polymerase chain reaction
Numerous studies have examined the occurrence, source, re-
activity, and transport of natural dissolved organic carbon
(DOC) in aquifers (Baker et al. 2000; Chapelle et al. 2009;
Longnecker and Kujawinski 2011;Shenetal.2015); howev-
er, to date, few have focused on the indirect associations be-
tween DOC and human health. This is in part due to the
diverse nature of organic compounds frequently encountered
in both polluted and unpolluted groundwater, in addition to
their variable levels of reactivity. While the precise composi-
tion of groundwater DOC is both temporally and spatially
variable (Clay et al. 1996; Goñi and Gardner 2003;Shen
et al. 2015), it typically comprises a relatively small propor-
tion of low molecular weight compounds (i.e. carbohydrates
and amino acids), and a larger proportion of more complex,
high molecular weight compounds (i.e. humic substances;
Artinger et al. 2000).
Organic matter of biological origin is the most frequently
oxidised substance in the aqueous environment and, due to the
reactive nature of a subset of biomolecular components
(Aiken 2002) groundwater DOC is indicative and/or causative
Published in the special issue BHydrogeology and Human Health^
*S. Regan
Department of Civil, Structural and Environmental Engineering,
University of Dublin Trinity College, Dublin 2, Ireland
Environmental Health and Sustainability Institute, Dublin Institute of
Technology, Graingegorman, Dublin 7, Ireland
School of the Natural and Built Environment, David Keir Building,
Queens University Belfast, Stranmillis Road, Belfast BT9 5AG, UK
Hydrogeol J (2017) 25:959967
DOI 10.1007/s10040-017-1583-3
with respect to a number of subsurface microbial and geo-
chemical processes. Some of these processes are considered
beneficial, e.g. denitrification (Clay et al. 1996; Pabich et al.
2001; Thayalakumaran et al. 2008); however, DOC enrich-
ment directly affects microbial oxygen availability and, thus,
subsurface microbial survival and mobility (Aravenaa et al.
1995; Chapelle et al. 2013; Thayalakumaran et al. 2015).
Moreover, high levels of dissolved organic matter (DOM)
present in groundwater may decrease optical clarity (or in-
crease turbidity), which can significantly reduce the efficacy
of specific treatment processes (e.g. irradiation) and compli-
cations can arise with the formation of DOC by-products fol-
lowing disinfection. Similarly, the presence of high levels of
DOC typically concurs with high concentrations of humic and
fulvic acids (Artinger et al. 2000), potentially resulting in in-
hibition of molecular laboratory analyses, most notably poly-
merase chain reaction (PCR) and enhanced contaminant mo-
bility; though in some polluted waters, e.g. sewage effluent,
proteins and carbohydrates may dominate DOC composition
(Flynn et al. 2015).
This paper provides a summary of DOC occurrence in
groundwater, followed by a brief overview of some issues
capable of indirectly affecting human health. Finally, a sum-
mary of where future research efforts might be focused with
respect to groundwater DOC and human health is provided.
Dissolved organic carbon in groundwater
DOC represents the carbonic fraction of dissolved organic
matter (DOM), typically accounting for >90% of the total
organic carbon (TOC) budget found in natural groundwaters
(Batiot et al. 2003a), with particulate organic carbon (POC)
accounting for the remainder. Analytically, DOC is
characterised as the organic fraction capable of passing
through a 0.45-μm filter (Evans et al. 2005; Kolka et al.
2008). Measured DOC concentrations in groundwater have
been shown to cover a wide range, from below detection
limits to >50 mg/l (Thurman 1985; Evans et al. 2005). As
shown in Table 1, a DOC range of 0.14 mg C/l is frequently
encountered in unpolluted aquifers, however, significantly
lower levels of DOC may be associated with aquifers receiv-
ing recharge where an organic horizon in a soil profile is
absent (to less than detection limits, typically in the order of
0.0060.05 mg/l) . Conversely, uncontaminated rivers are typ-
ically associated with DOC ranges of 110 mg C/l (Tao 1998),
although, as might be expected, elevated concentrations are
found in runoff from catchments characterised by extensive
areas of organic soils, e.g. peatlands (Kolka et al. 2008). Thus,
while DOC may be described as being relatively stable, in
both time and space, within many groundwater environments
(Pabich et al. 2001), this is not always the case, particularly
where significant surface-water/groundwater interaction
occurs, e.g. karst systems; accordingly, caution should be
employed in its interpretation.
Low DOC concentrations frequently associated with
groundwater contrast with those in pore water from overlying
soil horizons, with DOC ranges of 10200 mg C/l typically
reported (Wassenaara et al. 1991;Goldscheideretal.2006). It
is in the unsaturated subsurface zone that DOC is leached
from decomposing organic materials, with the principal bio-
geochemical processes affecting DOC removal in the vadose
zone being microbial utilization, oxidation, adsorption, and
metal co-precipitation (Wassenaara et al. 1991; Shen et al.
2015). These processes influence the transport of soluble or-
ganic carbon to and below the water table, in parallel with
environmental, climatic and geological factors. Typically, ap-
proximately 90% of surface-derived DOC is removed prior to
reaching the saturated zone (Pabich et al. 2001;Shenetal.
2015). Several studies have reported decreasing DOC concen-
trations in concurrence with increasing subsoil thickness and
aquifer depth (Pabich et al. 2001; Goñi and Gardner 2003;
Datry et al. 2004;Goldscheideretal.2006), with DOC con-
centrations at or close to zero reported in deep (> 1 km) and
old groundwaters (Pabich et al. 2001). Consequently, shallow
groundwater DOC characteristics are largely determined by
processes operating in the soil organic horizon (Trumbore
et al. 1992; Kalbitz et al. 2000), while the transfer of organic
matter remaining in solution is primarily dependent on vadose
zone thickness (Pabich et al. 2001; Batiot et al. 2003b;Goñi
and Gardner 2003), and the level of hydraulic connectivity
between subsoil horizons and the water table (Kalbitz et al.
The hydrological connectivity between the surface and
subsurface is important for the transfer of DOC into shallow
groundwater ecosystems, which will also be influenced by soil
properties/structure and land management practice. Whilst el-
evated groundwater DOC (generally considered to be approx-
imately 4 mg C/l) can occur naturally due to recharge being
influenced by discharge originating from wetland environ-
ments and the presence of sedimentary organic deposits, such
as coal, at depth (e.g. values of up to 200 mg C/l reported;
Artinger et al. 2000), high DOC is often associated with an-
thropogenic activities (Chomycia et al. 2008;Table1).
Additional organic matter from the increased use of organic
fertilisers, such as manure, has been reported from dairy farm
operations resulting in DOC concentrations up to 55 mg C/l
(Chomycia et al. 2008) and irrigated sugar cane fields (up to
82 mg C/l), due to organic-rich sugar mill by-products applied
as fertilizer and/or sugarcane sap released during harvest
(Thayalakumaran et al. 2015). DOC may also be sourced from
the hyporheic zonefor example, previous studies suggest
that surface water containing untreated waste has driven a rise
in groundwater DOC levels up to 14 mg/l in the Bengal aqui-
fer system of Bangladesh due to groundwater pumping from
irrigated croplands during the dry season (Bhattacharya et al.
960 Hydrogeol J (2017) 25:959967
2002;Harveyetal.2002). In extreme cases, aquifers polluted
by leachate from waste disposal such as a landfill, can contain
DOC concentrations as high as 300 mg/l (Christensen et al.
1999). Similarly, contamination of groundwater by leachate
from historical industrial activities, such as tannery facilities,
has been reported as the source of significant groundwater
plumes with DOC levels to as high as 400 mg/l (Davis et al.
Groundwater TOC and human health
The chemical composition of groundwater reflects the com-
position of water entering the subsurface, in addition to the
products of kinetically controlled reactions within the aquifer
matrix and overlying subsoil layers (Grützmacher et al. 2013).
The composition and bioavailability of DOM are key factors
affecting water quality, where observed increases in DOC
concentration may be indicative of changes in water quality.
For example, concentrations above background levels can
provide evidence of the occurrence of groundwater contami-
nation by organic compounds (Barcelona 1984;Harveyand
Barber 1992; Longnecker and Kujawinski 2011). Whilst there
are a number of issues that may be associated with TOC in
groundwater and human health, such as metal mobility
(Christensen et al. 1999), the following sections provide an
overview of three rarely examined issues with regard to
groundwater DOC measurements and their interpretation
within the context of human health.
Groundwater DOM, treatment approaches and efficacy
High levels ofDOM in water are known to cause aesthetic and
odour problems, while possibly promoting the growth and
proliferation of pathogenic bacteria (Pernthaler 2005;
Goldscheider et al. 2006; Gopal et al. 2007). Unpolluted
groundwater generally lacks any discernible colour and is
therefore considered optically clear (Chapelle et al. 2016),
though not necessarily in dynamic groundwater/surface-
water systems such as karst. However wastewater ingress to
groundwater recharge, due to an absence of natural subsurface
attenuation and/or localised preferential pathways (e.g. poorly
located or malfunctioning septic tanks), can increase ground-
water DOC concentrations and thus cause (dis)coloration via
elevated levels of humic materials (Westerhoff and Pinney
2000; Rittmann et al. 2002). The solubilization of heavy
metals by complexation with humic substances is known to
be of considerable importance in coloured natural waters
Tabl e 1 Selected groundwater
DOC concentrations from
unpolluted and polluted/enriched
Author/s DOC (mg C/l) Aquifer Impact
Artinger et al. 2000 0.31.5 Glacial sediment
Artinger et al. 2000 0.1 to 0.5 Sandstone bedrock
Baker et al. 2000 14 Fluvial sediment
Barcelona 1984 2.7 to <4 Glacial sediment
Batiot et al. 2003a 1.2 Karst bedrock
Datry et al. 2004 0.5 Glacial sediment
Wassenaara and Aravena 1991 1.42 Sandstone bedrock
Wassenaara et al. 1991 1.5 to 3.2 Glacial sediment
Anawar et al. 2003 >1 to <6 Fluvial sediment Sedimentary
Aravenaa et al. 1995 118 Glacial sediment Sedimentary
Artinger et al. 2000 <1 to >200 Glacial sediment Sedimentary
Artinger et al. 2000 517 Fluvial sediment Agriculture
Barcelona 1984 <5 to >20 Glacial sediment Drilling fluids
Batiot et al. 2003b 15 Dolomite bedrock Irrigation water
Bhattacharya et al. 2002 <1 to >14 Fluvial sediment Sedimentary
Chomycia et al. 2008 455 Fluvial sediment Dairy farming
Clay et al. 1996 <1 to >10 Glacial sediment Agriculture
Davis et al. 1994 2 to >400 Fluvial sediment Tannery leachate
Goñi and Gardner 2003 6 to >120 Marine sediments Irrigation water
Pabich et al. 2001 <123 Glacial sediment Eutrophication
Thayalakumaran et al. 2015 <4 to >80 Fluvial and marine sediment Sugar-cane fields
Note: Sedimentary refers to naturally emplaced geological formations
Hydrogeol J (2017) 25:959967 961
(Oliver et al. 1983). Also, the persistence of high DOC loading
has significant implications for the fate of other contaminants
such as pesticides, pathogens, and pharmaceuticals, as hypox-
ic conditions may restrict the degradation of many carbon-
based compounds (Chomycia et al. 2008), though in some
instances it may promote it.
There are numerous water treatment technologies applied
for DOC reduction such as flocculation and filtration engi-
neering techniques. Advanced treatment typically employs
ozonation, which cleaves the unsaturated bonds in the aromat-
ic molecular components of humic materials, thereby decreas-
ing colour, in addition to increasing the degradability of or-
ganic molecules (Rittmann et al. 2002). While ozonation has
been shown to reduce DOC, the magnitude of reduction is
limited (< 10%); accordingly, additional treatment processes,
typically engineered biofiltration approaches, are required to
provide further DOM reductions (Drewes and Jekel 1998).
However, when wastewater is to be released to groundwater,
further treatment can be achieved by soil aquifer treatment
(SAT), which utilises the attenuation properties of the subsoil
zone and concurrently recycles wastewater while augmenting
recharge (Drewes and Jekel 1998). SAT systems are typically
employed in areas characterised by limited conventional
freshwaterresources and overexploited local aquifers, e.g. arid
regions (Kim and Yu 2007), developing countries (Westerhoff
and Pinney 2000), and heavily urbanised environments
(Drewes and Jekel 1998).
Drinking-water treatment facilities, including the pre-
treatment of SAT recharge, typically involves disinfection via
chlorination in order to ensure satisfactory potable water sup-
plies and to prevent microbial growth during distribution
(Chomycia et al. 2008;Uyaketal.2008); however, this ap-
proach may be problematic as chlorine may react with DOC to
produce potentially harmful disinfection by-products (DBPs)
including trihalomethanes (THMs) and haloacetic acids
(HAAs), both of which are suspected carcinogens (WHO
2011). The concentrations of both are currently regulated
across the European Union by Council Directive 98/83/EC
and in the United States by the US Environmental Protection
Agency (Safe Water Drinking Act). The total concentration of
DBPs present and the distribution of individual compounds in
chlorinated water depend upon the initial raw water character-
istics, in addition to operational parameters during the treatment
process such as pH and temperature (Kim and Yu 2007;Uyak
et al. 2008). The complex polymeric properties of humic sub-
stances result in significant difficulties with respect to effective
environmental characterisation. Previous studies have shown
that humic substances are imperative precursors to the devel-
opment of DBPs and strongly influence the formation potential
of THMs, much more so than the non-humic faction of organic
matter (Westerhoff and Pinney 2000;KimandYu2007).
Investigations of DOC treatment processes consistently
confirm that biodegradation of DOC represents the dominant
removal mechanism during treatment, with preferential re-
moval of low molecular weight DOC (Drewes and Jekel
1998; Westerhoff and Pinney 2000;KimandYu2007).
DOC removal typically exhibits moderate (50%) to high
(90%) removal efficiencies (Quanrud et al. 2003a).
However, the bias towards refractory humic substance com-
ponents remaining in DOC solution complicates treatment
efficacy as DBP precursors with THM formation potential
(THMFP) are persistent factions of DOC and whose reactivity
may increase post-treatment due to removal on non-reactive
species (Westerhoff and Pinney 2000; Quanrud et al. 2003b).
Nevertheless, whilst associations have been found between
increased instance of specific cancers (e.g. rectal, kidney)
and consumption of chlorinated drinking water (Kuo et al.
2010;Liaoetal.2012), few studies have been carried out on
demonstrated cancer occurrences as a result of THM/DBP
presence in potable groundwater supplies. Subsequently, de-
spite engineered artificial recharge systems being commonly
used to remove DOC from recycled treated wastewaters, little
research has been conducted on the presence of DBPs in
groundwater systems receiving artificial recharge.
Organic matter and colloidal mobility
BColloidal contaminants^include some of the earliest known
pollutants recognised to impact water quality such as patho-
genic microorganisms (bacteria, viruses and protozoa; Macler
and Merkle 2000). More recent investigations have
recognised that natural colloidal materials can facilitate the
transport of low solubility substances (Kretzschmar et al.
1999), while, by products of recent technological develop-
ments, including engineered nanoparticles (Nuttall and Kale
1994), represent emerging contaminants of concern that may
also impact human health (Troester et al. 2016). As frequently
alluded to throughout the current Hydrogeology Journal spe-
cial issue Hydrogeology and Human Health, the importance
of aquifers as drinking water sources in many parts of the
world cannot be overstated, and thus, an increase in under-
standing of colloid mobility in the subsurface will likely prove
fundamental to the development of successful source protec-
tion strategies (Flynn et al. 2015; Hunt and Johnson 2016)as,
in contrast to solutes, pathogens can cause infection at exceed-
ingly low levels of exposure and are often associated with
rapid (<10 year) subsurface flow (Hunt and Johnson 2016).
In spite of considerable recent advances made in under-
standing fundamental processes responsible for attenuation
under controlled (laboratory) conditions, factors influencing
colloidal fate and transport in natural porous media remain
poorly defined. Complicating factors include the higher de-
grees of compositional and textural heterogeneity encountered
in natural deposits (Flynn et al. 2015), in addition to other
factors such as the co-occurrence of suites with other contam-
inants that may promote or inhibit colloid mobility.
962 Hydrogeol J (2017) 25:959967
At present, the conceptual understanding of colloid mobil-
ity largely relies on approaches developed for engineered filter
beds, where removal capacity has been shown to depend on
the chemical and physical properties of the contaminants, col-
lector surfaces (i.e. grains and fissure walls), and the inorganic
hydrochemistry of the host solution, most notably ionic
strength and pH (Kretzschmar et al. 1999). The role of DOC
adds another layer of complexity to effective characterisation.
Despite its widespread occurrence in natural waters and the
frequently observed relationship between DOC and colloids
in certain polluted settings, e.g. sewage impacted groundwater
(Flynn et al. 2012), colloid-organic matter interactions have
received relatively little research attention until recently
(Bradbury et al. 2013;Yangetal.2015). Qualitative observa-
tions have indicated that diverse mechanisms may operate,
ranging from promotion to inhibition of mobility
(Kretzschmar et al. 1999). The contrasting responses are per-
haps unsurprising, given the range of organic compounds
present in the wider environment in both natural and polluted
settings (Harvey et al. 2010a,2010b).
The capacity of organic matter (OM) to stabilise colloids in
suspension has been recognised for some time (Kretzschmar
et al. 1997), while more recent studies have begun to shed
light on the capacity of OM to influence the attenuation ca-
pacity in saturated porous mediafor example, Yang et al.
(2010) carried out multiple pulse dynamic column studies at
laboratory scale, coupled with random sequential adsorption
modelling (RSA) of tracer breakthrough curves to quantify the
influence of OM on colloid mobility. This approach provided
a basis for further investigations to highlight the complexity of
OM-colloidal contaminant interactions in the subsurface en-
vironment. Using RSA modelling, Yang et al. (2011)
employed engineered particles (fluorescent microspheres) to
show how changes in ionic strength and pH, with comparable
compositions to those observed in natural waters, dramatically
altered the capacity of a well characterised humic acid to in-
fluence the colloid attenuation capacity of a saturated sand;
such changes may contribute to increases in colloid contami-
nation in groundwaters following recharge events, as noted by
Hunt and Johnson (2016).
Subsequent studies further highlighted the complexity of
colloid-OM interactions. Flynn et al. (2012) employed a well-
characterised protein (Bovine Serum Albumin) in place of
humic acid, to reveal comparable blocking responses at low
concentrations, whereas application of higher concentrations
generated breakthrough curves reflecting Bripening^behav-
iour. Furthermore, Yang et al. (2012) have identified addition-
al processes of potential hydrogeological significance, includ-
ing the capacity of compounds to dissolve favourable deposi-
tion sites, such as iron oxide patches on grain surfaces, thus
promoting greater colloid mobility.
Despite progress in characterising colloid-OM interactions
in the laboratory, DOCs influence on colloid migration in
groundwater systems remains largely uncharacterised.
Nonetheless, realistic conceptual models provide a reliable
basis for upscaling and identification of potentially relevant
settingsfor example, while the impacts of changes in water
chemistry on colloid mobility are expected to be of greater
significance in surface water systems,similar changes can also
be anticipated in karst, where field experimentation, albeit in
the absence of organic matter, has demonstrated the capacity
of hydrochemical changes to effectively mobilise particles
deposited under conditions more conducive to detachment
(Flynn and Sinreich 2010). Similarly, as studies employing
DOC have demonstrated, contrasts in concentration, which
occur between the margins of a contaminant plume and its
centre may give rise to contrasting colloid attenuation capacity
(Harvey et al. 2011). This information, coupled with the find-
ings of Flynn et al. (2012) suggests that some DOC may be
capable of promoting or inhibiting colloid mobility at different
stages of a plumesdevelopment. Furthermore, alterations to
the content/configuration of deposited OM, arising from pro-
cesses including OM degradation and/or changes in
hydrochemistry, may give rise to temporal changes in the ca-
pacity of aquifers to disinfect groundwater.
From the aforementioned, it is clear that characterising the
influence of DOC on colloidal contaminant occurrence in
aquifers is a complex topic; moreover, effective characterisa-
tion of colloid-OM interactions at the field scale continues to
present a significant challenge, largely due to inherently lower
levels of experimental control. Nevertheless, it is widely ac-
knowledged that findings from laboratory-based investiga-
tions require complementary in-situ testing in order to accu-
rately assess the relative importance of a potentially vast range
of mechanisms in which OM may influence colloid fate and
transport. Field-based artificial tracer testing, when employed
within a realistic hydrogeological framework, which con-
siders findings of studies completed under more controlled
(laboratory) conditions, represents a useful approach to better
understanding these processes (Flynn et al. 2015). Findings
from limited studies completed to date (e.g. Harvey et al.
2011; Metge et al. 2010;Pieperetal.1997) suggest that this
will prove a fruitful area of research for future investigations,
ultimately leading to more scientifically defensible groundwa-
ter protection strategies.
Inhibition of polymerase chain reaction (PCR)
Those who drink groundwater that has not been disinfected
are at increased risk of infection and disease from pathogenic
microorganisms (Macler and Merkle 2000; Borchardt et al.
2012; Hynds et al. 2014a). Polymerase chain reaction (PCR)
is increasingly being employed as the standard method for
detection and characterization of (pathogenic and non-
pathogenic) microorganisms and genetic markers in a variety
of water types including groundwater (Schrader et al.2012). A
Hydrogeol J (2017) 25:959967 963
recent systematic review of groundwater contamination in the
United States and Canada found that almost three quarters of
relevant studies from 1990 to 2013 employed PCR as the
principal pathogen detection method (Hynds et al. 2014b).
The method employs a process whereby nucleic acid se-
quences (i.e. microbial Bbuilding blocks^) are enzymatically
amplified from non-detectable to detectable levels (Kong et al.
2002; De Man et al. 2014). During the process, strands of the
DNA double helix, initially present in very small numbers, are
physically separated via DNA thermal melting, followed by
highly selective amplification by DNA polymerase.
Amplification usually takes place over 3545 cycles, resulting
in exponential multiplication of the number of DNA frag-
ments of interest originally present (Girones et al. 2010;
Ramírez-Castillo et al. 2015). Since its development in the
early 1980s, PCR has become a rapid, highly specific, low
cost method for microbial detection, and is now regularly used
in the field of environmental science (Abbaszadegan et al.
1999; Schrader et al. 2012). Moreover, due to increasing ac-
curacy, in parallel with decreasing costs, these techniques are
now frequently employed for quantitative risk assessment and
regulation of both drinking and recreational waters (Gibson
et al. 2012).
Despite the multiple advantages associated with PCR, the
process is prone to inhibition by naturally occurring sub-
stances (inhibitors) in groundwater; PCR inhibitors represent
a diverse group of organic and inorganic chemicals including
urea, phenol, ethanol, complex polysaccharides, bacterial de-
bris, metal ions, humic acids, and tannic acid, among others
(Radstrom et al. 2004;Schraderetal.2012). The presence of
varying concentrations of inhibitory compounds in water sam-
ples will disrupt amplification of target nucleic acids via a
number of biochemical processes (Shain and Clemens 2008;
Radstrom et al. 2008). This results in partial or total PCR
inhibition, leading to decreased sensitivity or false-negative
results, respectively. Accordingly, this potential under-
estimation represents the primary source of concern with re-
spect to identifying poor water quality using PCR
As previously outlined, humic acids and other humic sub-
stances are typically present in groundwater with high levels
of dissolved organic carbon, (Artinger et al. 2000;Rocketal.
2010). This in turn will interact with template DNA and the
polymerase, even at low concentrations, thus preventing the
enzymatic reaction (Sutlovic et al. 2008). It is important to
note that levels of inhibition will primarily depend on the
relative concentration of the inhibitor and not its source. A
recent PCR inhibition study undertaken by Gibson et al.
(2012) comprised 2187 groundwater samples taken from do-
mestic and municipal boreholes associated with relatively
deep sandstone aquifers in Wisconsin. Overall, 4% of ground-
water samples were associated with false-negative results for
viral pathogens due to the effects of inhibitory compounds,
with inhibitory concentrations in groundwater samples found
to span four orders of magnitude (Gibson et al. 2012). Results
suggest that numerous factors including sample volume, site
location and seasonality affected inhibition levels; it was not
possible to spatially assess or predict inhibition potential, and
thus it is recommended that all groundwater samples be
analysed for inhibition prior to PCR, and particularly when
sampling is associated with a human health event and/or
(expected) high groundwater DOC concentrations, i.e.
groundwater from karstic areas and peatlands (Borchardt
et al. 2003; Kolka et al. 2008;Gibsonetal.2012).
The current paper presents an overview of the occurrence of
dissolved organic carbon (DOC) in groundwater, and its im-
plications for human health linked to interactions with other
substances. Treatment processes for DOM effectively reduce
DOC concentrations; however, humic substances are difficult
to remove from solution and react with chlorine in the disin-
fection process to produce DBPs, most notably THMs, many
of which are suspected carcinogens. Whilst connections be-
tween human cancer occurrences and ingestion have been
made for treated surface-water supplies, there are no such
studies from supplies using publicly supplied groundwater.
Considering many domestic and public drinking water wells
are often located in close proximity to arable and agricultural
activities that require treatment, this may be a significant and
persistent, yet poorly understood, health risk, both in develop-
ing and developed countries. Moreover, the use of reclaimed
and treated wastewater for engineered aquifer recharge is an
increasingly common practice in many regions of the world,
which indicates that aquifers utilised by human populations,
both in urban and rural areas, may already have undesirable
DBP concentrations.
Until recently, relatively little attention had been given to
mechanisms behind the interactions between OM and colloi-
dal contaminants, and their influence on the mobility of path-
ogenic microorganisms in the subsurface. The capacity to
quantify these processes now provides a means to more con-
fidently investigate the behaviour of OM in saturated porous
media and for colloidal contaminant transport in aquifers.
Further development of this topic, necessary to protect
groundwater supplies, will require investigations spanning a
range of investigative scales and disciplines. Although there
remains a need for further laboratory-based investigations to
identify fundamental processes, a need for further field-scale
investigations is outstanding if the importance of these pro-
cesses in natural systems is to be defined. The role of the
hydrogeologist is anticipated to prove fundamental in bridging
this divide.
964 Hydrogeol J (2017) 25:959967
PCR techniques are now frequently used for the detec-
tion, identification, and quantification of waterborne path-
ogensfor example, Sezen et al. (2014) recently reported
on a large waterborne multi-pathogen gastroenteritis out-
break in Turkey, which was found to be caused by con-
sumption of contaminated groundwater from historic
neighbourhood fountains. This investigation comprised
the use of real-time multiplex PCR, with results proving
the source of the outbreak, in addition to the causative
pathogens (Shigella sonnei, astrovirus, and norovirus).
Accordingly, the study authors were able to provide fast,
reliable evidence-based recommendations pertaining to
both avoidance of new cases and treatment of existing
cases, thereby significantly contributing to public health
in the affected region. However, PCR inhibition by humic
substances is capable of resulting in significant under-
estimation or false-positives (Abbaszadegan et al. 1999;
Radstrom et al. 2008;Schraderetal.2012), thus poten-
tially resulting in a failure to correctly detect the source of
an ongoing human health event associated with ground-
water supplies. While groundwater derived from specific
settings may be expected to comprise high levels of PCR
inhibitors due to high groundwater DOC concentrations,
i.e. karstic areas and peatlands (Borchardt et al. 2003;
Kolka et al. 2008), and should therefore be systematically
analysed for inhibition prior to the use of PCR, a recent
studybyGibsonetal.(2012) found that 4% of ground-
water samples from deep non-karstic aquifers in the US
(n= 2187) produced false-negative results. Moreover, re-
sults from the same study showed that sample volume,
site location and seasonality affected inhibition levels;
thus, it is recommended that, in the short-term, all ground-
water samples be systematically analysed for levels of
inhibition due to the presence of humic acids prior to
PCR, and in the medium- to long-term, regionally or
hydrogeologically specific studies seek to quantify tempo-
ral variation associated with PCR inhibitors in groundwa-
ter, particularly in vulnerable areas, and those associated
with previous waterborne outbreaks.
This paper has identified three key issues associated
with DOC in groundwater, namely the presence of
DBPs, colloidal transport mechanisms and usage of PCR
techniques, in treated and/or untreated groundwater used
in municipal water supply. Future research efforts on
these issues should be directed with respect to groundwa-
ter DOC and human health, as currently, these issues are
under-represented in published literature. Other issues of
concern not covered here include optical clarity and the
presence of chromophoric dissolved organic matter, which
effects ultraviolet/visible light absorbance, and this also
warrants increased investigation in coloured municipal
groundwater supplies, as a means to better understand
the factors and processes leading to DOC enrichment.
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... Zeng et al. (2022) inferred that organic matter might form toxic substances with alkaline earth elements and can also facilitate F-release. DOC with different types of organic compounds is ubiquitous in natural waters that originate from geogenic and anthropogenic sources (Regan et al. 2017). It was reported that the DOC contents in groundwater were higher in CKDu hotspots when compared to non-CKDu regions (Cooray et al. 2019). ...
... 4‰ (Jayathunga et al. 2020). Usually, groundwater shows DOC values between 0.017 and 0.17 mmol/L due to natural organic matter, and higher levels indicate groundwater contamination by organic pollutants (Regan et al. 2017). The DOC in groundwater in the CKDu hotspots is likely provided by allochthonous natural organic matter. ...
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Quality of drinking water has become a significant concern with chronic kidney disease of uncertain aetiology (CKDu), particularly in the dry zone regions of Sri Lanka. In this study, groundwaters consumed by biopsy-proven CKDu patients were assessed for identifying possible hydrogeochemical risk factors because histopathological observations are still considered the best method for identifying CKDu cases. Major anions, cations, and 22 trace elements in groundwater were measured in addition to dissolved organic carbon (DOC) and its isotope ratios (expressed as δ13CDOC). Variations of groundwater quality were monitored monthly in five selected wells. The data were compared with a non-endemic region with a similar climatic and socio-economic background. Groundwater used by CKDu cases is predominantly of the Ca–Mg–HCO3 type. Over 88% of the samples showed excess hardness, while 44% showed high fluoride (F−) contents (> 0.60 mg/L). These two parameters are noticeably different compared to groundwater from non-endemic regions with similar geoenvironmental backgrounds. The dissolved organic carbon (DOC) content varied from 0.06 to 0.30 mmol/L with a mean value of 0.15 mmol/L in CKDu wells. In most cases, known nephrotoxic trace elements such as As, Pb, Cd, and U were found to be lower than 0.01 µg/L. Seasonally, F− and Si4+ (as H4SiO4) content fluctuated, even though monsoon rain inputs did not seem to alter the geochemical composition. Principal component analysis (PCA) indicated that the dissolution of aquifer minerals and ion exchange processes are most likely responsible for the groundwater geochemistry in the study terrain. This study highlights the importance of F−, hardness (Ca2+ + Mg2+), and Si4+ in groundwaters of CKDu-related tropical terrains. The synergetic impact of these parameters needs further systematic studies, ideally combined with animal models, to unravel the aetiological mechanisms of CKDu.
... Groundwater was contaminated because of dissolved organic carbon (DOC) from landfill leachate, which combined with the metals to produce complexes. The presence of DOC accelerated the metals' movement [44]. Dissolved organic carbon (DOC) was studied to determine its properties and markers of wastewater origin in both reclaimed wastewaters and groundwater. ...
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The quality of groundwater has been severely impacted by urbanization around coasts. The change in climate and land use patterns has deteriorated the quality and availability of groundwater. One of the main issues in contemporary groundwater quality research is dissolved organic carbon (DOC) in the water. The influence of DO, water level and water temperature on DOC in groundwater was identified in the current study by sampling 68 groundwater samples. The analytical results revealed that ~18% of total samples have DOC > 5 mg/L. The groundwater samples represented in the urban regions show high DOC. The samples with higher DOC correlated positively with dissolved inorganic ions, such as Ca, K, NO3, Fe and DO. Domestic wastewater, agricultural runoff and local geology all have an impact on the DOC of groundwater. Groundwater chemistry is shown to be controlled by both aerobic and anaerobic conditions based on the DOC’s interactions with other ions. The study interrelates various sources, such as land use, geology, water level and temperature, to the DOC in groundwater and infers that the levels are higher in shallow groundwater, predominantly around the built-up region followed by the agricultural region. The temperature changes enhance the DOC in groundwater due to the variation in microbial activity. The shallow water level with a lower temperature shows the maximum DOC. Apart from the sediment organic matter and microbes, the study also attributes land use pattern to the source of DOC in groundwater.
... This unbound fraction f unbound can be estimated according to (Burkhard 2000) where C DOC is the concentration of DOC in water in kg DOC/L w and C POC is the concentration of POC in water in kg POC/L w . For the specific experiments with H. azteca that we investigate here, we will calculate with a typical DOC concentration of about 1 mg DOC/L w (personal correspondence with Prof. Schlechtriem, flow-through system, Regan et al. (2017) reports more than 90% of TOC in water sources to be DOC). This leads to a substantial decrease in f unbound for high log K ow , see Figure S1. ...
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Bioconcentration tests using the freshwater amphipod Hyalella azteca as an alternative to conventional fish tests have recently received much attention. An appropriate computational model of H. azteca could help in understanding the mechanisms behind bioconcentration, in comparison to the fish as test organism. We here present the first mechanistic model for H. azteca that considers the single diffusive processes in the gills and gut. The model matches with the experimental data from the literature quite well when appropriate physiological information is used. The implementation of facilitated transport was essential for modeling. Application of the model for superhydrophobic compounds revealed binding to organic matter and the resulting decrease in bioavailable fraction as the main reason for the observed counterintuitive decrease in uptake rate constants with increasing octanol/water partition coefficient. Furthermore, estimations of the time needed to reach steady state indicated that durations of more than a month could be needed for compounds with a log Kow > 8, limiting the experimental applicability of the test. In those cases, model-based bioconcentration predictions could be a preferable approach, which could be combined with in vitro biotransformation measurements. However, our sensitivity analysis showed that the uncertainty in determining the octanol/water partition coefficients is a strong source of error for superhydrophobic compounds.
... For instance, a rising DOC concentration in many upland catchments of the United Kingdom represents a challenge for drinking water quality, in particular due to the role of DOC as a precursor in the formation of trihalomethanes [9]. Measured DOC concentrations from natural/unpolluted groundwater are typically below 4 mg L −1 , above which anthropogenic influence and/or contamination issues might occur [36]. In nature, organic matter originates from plant, microbial, and animal products both in the forms of metabolized products and their decomposing products. ...
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Dissolved carbon has been widely investigated in natural rivers worldwide. However, it has been rarely studied in riverine system of farming regions, where small streams have been usually modified by a water gate and flood levee. This study was conducted to investigate dissolved organic and inorganic carbon (DOC, DIC) in artificially modified tributary streams, namely the Desheng and Shuangqiao-Shiba streams, in a farming region of the lower Yangtze River basin. The results showed that the DOC and DIC concentrations had remarkable temporal–spatial variability in the Desheng and Shuangqiao-Shiba streams. The mean DOC concentrations were 5.4 and 6.7 mg L−1 in the Desheng and Shuangqiao-Shiba streams during the period of about 1 year, while the DIC concentrations were 14.0 and 9.6 mg L−1 in both streams, respectively. The DOC and DIC concentrations mainly showed the linear decreasing trends from source through to export in the spring, summer, autumn, and winter. The DOC concentration was almost always lower than the DIC concentration. The DOC concentration was positively correlated with the DIC concentration in the Desheng stream over the four seasons, indicating that the DOC and DIC potentially had similar sources. The DOC and DIC concentrations increased with sewage discharge, which introduced a potential hazard to human health. The water gate and flood levee in the Desheng and Shuangqiao-Shiba streams were constructed for discharging floods and recharging irrigation in the farming region, and their effects on dissolved carbon require further research.
... As seen from Figure S2a,b, molecules with MW > 30 kDa of DOC and BDOC were averaged at 27.6 and 24.5%, and those with MW < 1 kDa were 40.3 and 50.8%, respectively, almost half of the total. With these high DOC and BDOC concentrations, the biological stability and safety of the drinking water supply are difficult to guarantee [33]. Limited removal of DOC was also observed during the conventional water treatment processes (coagulation, sedimentation, and sand filtration) in a previous research [34]. ...
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The biodegradable dissolved organic carbon (BDOC) in micro-polluted water sources affects the drinking water quality and safety in the urban water supply. The conventional technology of “coagulation-sedimentation-filtration” in a water plant located in the lower reaches of the Yangtze River removed dissolved organic carbon (DOC) with a molecular weight (MW) > 30 kDa effectively, but the BDOC elimination only ranged 27.4–58.1%, due to their predominant smaller MW (<1 kDa), leading to a high residual BDOC of 0.22–0.33 mg/L. To ensure the biological stability of drinking water, i.e., the inability to support microbial growth (BDOC < 0.2 mg/L), a pilot-scale ultrafiltration process (UF, made of aromatic polyamide with MW cut-off of 1 kDa) was operated to remove BDOC as an advanced treatment after sand-filtration. Results showed the membrane flux decreased with the increase in the influent BDOC concentration and decrease in operating pressure. With an operating pressure of 0.25 MPa, the BDOC removal by UF reached 80.7%, leading to a biologically stable BDOC concentration of 0.08 mg/L. The fouling of the membrane was mainly caused by organic pollution. The H2O2–HCl immersion washing method effectively cleaned the membrane surface fouling, with a recovery of membrane flux of 98%.
... Groundwater from glacial sand and gravel deposits overlaid by organic rich sediments may contain DOC concentrations higher than 15 mg DOC/L (Artinger et al., 2000) and often correlates with anaerobic groundwater conditions (Kunkel et al., 2004). According to Regan et al. (2017), Concentrations in groundwater above 4 mg DOC/L may also indicate anthropogenic contamination issues such as the application of manure. ...
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Denitrification in groundwater is an important process that helps to maintain environmental standards, yet there are very few studies that determine the spatial variation of denitrification conditions in aquifers on a regional scale. We introduce a procedure to derive spatially continuous estimates of denitrification conditions in groundwater based on the interpolation of measurements of the redox-sensitive parameters oxygen, nitrate, iron, manganese and DOC, combined with the quantification of denitrification using a 2D-hydrodynamic model based on first-order reaction kinetics. We applied this procedure to Germany, using measured values from more than 24,000 groundwater monitoring sites from 2007 to 2016. Annual concentrations of the five parameters at the monitoring sites were regionalized using an optimized, iterative inverse distance weighting procedure within 15 aquifer typologies for spatial delineation. The annual grids (2007-2016) of each parameter were then overlaid and a median over time was calculated. Discrete ranks were then assigned to the concentrations of each parameter based on their redox class, and ultimately, after overlaying the five parameters, a mean value was calculated describing the nitrate degradation conditions in groundwater. After assigning half-life times and reaction constants to those denitrification conditions, we quantified denitrification in groundwater using the hy-drodynamic model WEKU. To assess the plausibility of the derived denitrification in groundwater, we compared our results with the proportion of denitrified nitrate determined with the N2/Ar method at 820 groundwater monitoring wells in three German Federal States, which showed an overall good agreement. Accordingly, the method presented here is suitable to be used for the regionally differentiated derivation of denitrification conditions in groundwater. For regions with denitrifying groundwater conditions, the results provide an explanation for frequently observed discrepancies between high nitrate emissions from the soil and low nitrate concentrations in the groundwater of intensively used agricultural areas.
... Organic carbon and nitrogen, especially DOC and DON, are important considerations in drinking water because of their potential to contribute to disinfection byproduct (DBP) formation and metal binding (Regan et al., 2017;Westerhoff & Mash, 2002). Particulate organic carbon can similarly affect metal toxicity. ...
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Wildfires have increased in frequency in many ecosystems, with implications for human health and the environment, including water quality. Increased fire frequency and urbanization also raise the prospect of fires burning into urban areas, mobilizing pollutants few have considered to date. As a result, water quality managers lack information to anticipate, respond to and potentially mitigate wildfire impacts. Here, we reviewed the scientific literature to assess wildfire effects on response endpoints of a conceptual model linking fire to water quality, quantifying response directionality, magnitude and duration. Physically, water yield, sediments, and temperature all increased post‐fire. Chemically, nutrients, ions, organic chemicals, and metals increased in burned watersheds, sometimes by orders of magnitude over pre‐fire or reference conditions. In select cases, post‐fire concentrations exceeded aquatic life criteria or drinking water standards, at times even in the finished drinking water. Biological assemblages commonly declined after post‐fire runoff events. The duration of effects was less than 5 yr for most endpoints (e.g., metals) on average following fire, although effects did extend 15 yr or more in some individual cases. We found only a few studies on pollutants mobilized from wildfire impacted urban areas with benzene contamination in drinking water and high metal concentrations in ash prominent exceptions. Overall, this review provides a resource for understanding wildfire impacts on water quality endpoints, with the goal of informing the response of managers and other decision makers to this growing problem.
Following the 2021 Marshall Fire in Colorado, this study was conducted to better understand private well and plumbing damage and to develop public health guidance. More than 20 post‐fire drinking water well guidance documents with varied recommendations were found. Approximately 227 wells were located in the fire footprint. Seventeen properties were visited, and a subset of wells were sampled for organic and inorganic contaminants. Property debris was also collected. Benzene, toluene, and 19 semi‐volatile organic compounds (SVOCs) were detected in water extracts of property debris. No wells contained volatile organic compound contamination. Two shallow wells (12 and 15 ft) had debris contamination; one well contained notable SVOC contamination. One multi‐home unregulated well system was extensively damaged, lost pressure, and had not been repressurized 11 months after the fire due to financial and technical challenges. Study results highlight the need for follow‐up work to understand well system damage and household response.
The dissolved organic matter (DOM) should be purified for safe drinking water due to disinfection by-products (DBPs) produced by disinfectants reaction with DOM. Current research on groundwater in the chronic kidney disease with unknown etiology (CKDu) zone of the North Central Province (NCP) in Sri Lanka has focused mainly on aquatic chemistry, with limited attention paid to the spatial distribution, compositional sources and factors of DOM. Therefore, the structure, composition, source and spatial distribution of the DOM of two kinds of groundwater samples collected from dug well and tube well in the NCP during the wet season were determined, compared and analyzed by analytical tools such as parallel factor analysis (PARAFAC). Results show that the average concentrations of TOC in these two groundwater samples are generally higher than 5.0 mg/L, and the concentration of TOC in the groundwater of the shallow weathered aquifer is higher than that of the deep hard rock aquifer, while its distribution of the two aquifers are on contrary. The DOM in the dug well has three types and four components, including humus-like component C1 (33.36%) and C2 (38.60%), protein-like component C3 (13.09%) and heterogeneous organic component C4 (14.95%). In the tube well, two types and two components of the DOM are determined, including humus-like component CⅠ (69.80%) widely existing in natural water and soluble microbial by-product CⅡ (30.20%) produced by microbial community activities. In the dug well, DOM is mainly exogenous input, the higher ion concentration in water affected the fluorescence intensity of humus and protein components. And in the tube well, DOM has obvious endogenous characteristics, and higher pH value may inhibit the production of protein like fluorescent substances to a certain extent.
Hydrogeochemical evaluation of groundwater resources is of paramount significance in the tropics as it aids identification of safe and sustainable water resources. Evaluation of heavy metals in water is necessary as they integrate into the food chain and pose deleterious effects on human and aquatic life. To identify the extent of heavy metal occurrence in groundwater, 40 samples were collected seasonally from dug wells located in agriculture-intensive areas and analysed for physicochemical parameters and heavy metals. Water quality and pollution indices were used to evaluate overall groundwater quality and threat to humankind. The heavy metal concentrations in groundwater were observed in the increasing sequence of Zn > Cu > Pb > Ni > Co (post-monsoon) and Zn > Pb > Cu > Ni > Co (pre-monsoon). Heavy metal pollution index (HPI) revealed that the dissolved heavy metal content was found below critical value. Correlation analysis (CA) and principal component analysis (PCA) revealed that the groundwater hydrochemistry is influenced by geogenic (rock-water interaction, precipitation, simple dissolution, and base-exchange reactions) and anthropogenic sources. The results of this study will help in developing a long-term groundwater monitoring system for metal pollution, sustainable management, and conservation of peri-urban groundwater resources to achieve water security.
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High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical aquifer in southern Bangladesh, chemical data imply that arsenic mobilization is associated with recent inflow of carbon. High concentrations of radiocarbon-young methane indicate that young carbon has driven recent biogeochemical processes, and irrigation pumping is sufficient to have drawn water to the depth where dissolved arsenic is at a maximum. The results of field injection of molasses, nitrate, and low-arsenic water show that organic carbon or its degradation products may quickly mobilize arsenic, oxidants may lower arsenic concentrations, and sorption of arsenic is limited by saturation of aquifer materials.
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Water quality affects many aspects of water availability, from precluding use to societal perceptions of fit-for-purpose. Pathogen source and transport processes are drivers of water quality because they have been responsible for numerous outbreaks resulting in large economic losses due to illness and, in some cases, loss of life. Outbreaks result from very small exposure (e.g., less than 20 viruses) from very strong sources (e.g., trillions of viruses shed by a single infected individual). Thus, unlike solute contaminants, an acute exposure to a very small amount of contaminated water can cause immediate adverse health effects. Similarly, pathogens are larger than solutes. Thus, interactions with surfaces and settling become important even as processes important for solutes such as diffusion become less important. These differences are articulated in “Colloid Filtration Theory”, a separate branch of pore-scale transport. Consequently, understanding pathogen processes requires changes in how groundwater systems are typically characterized, where the focus is on the leading edges of plumes and preferential flow paths, even if such features move only a very small fraction of the aquifer flow. Moreover, the relatively short survival times of pathogens in the subsurface require greater attention to very fast (<10 year) flow paths. By better understanding the differences between pathogen and solute transport mechanisms discussed here, a more encompassing view of water quality and source water protection is attained. With this more holistic view and theoretical understanding, better evaluations can be made regarding drinking water vulnerability and the relation between groundwater and human health.
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Concentrations of dissolved organic matter (DOM) and ultraviolet/visible light absorbance decrease systematically as groundwater moves through the unsaturated zones overlying aquifers and along flowpaths within aquifers. These changes occur over distances of tens of meters (m) implying rapid removal kinetics of the chromophoric DOM that imparts color to groundwater. A one-compartment input-output model was used to derive a differential equation describing the removal of DOM from the dissolved phase due to the combined effects of biodegradation and sorption. The general solution to the equation was parameterized using a 2-year record of dissolved organic carbon (DOC) concentration changes in groundwater at a long-term observation well. Estimated rates of DOC loss were rapid and ranged from 0.093 to 0.21 micromoles per liter per day (μM d⁻¹), and rate constants for DOC removal ranged from 0.0021 to 0.011 per day (d⁻¹). Applying these removal rate constants to an advective-dispersion model illustrates substantial depletion of DOC over flow-path distances of 200 m or less and in timeframes of 2 years or less. These results explain the low to moderate DOC concentrations (20–75 μM; 0.26–1 mg L⁻¹) and ultraviolet absorption coefficient values (a254 < 5 m⁻¹) observed in groundwater produced from 59 wells tapping eight different aquifer systems of the United States. The nearly uniform optical clarity of groundwater, therefore, results from similarly rapid DOM-removal kinetics exhibited by geologically and hydrologically dissimilar aquifers.
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Gravel aquifers act as important potable water sources in central western Europe, yet they are subject to numerous contamination pressures. Compositional and textural heterogeneity makes protection zone delineation around groundwater supplies in these units challenging; artificial tracer testing aids characterization. This paper reappraises previous tracer test results in light of new geological and microbiological data. Comparative passive gradient testing, using a fluorescent solute (Uranine), virus (H40/1 bacteriophage), and comparably sized bacterial tracers Escherichia coli and Pseudomonas putida, was used to investigate a calcareous gravel aquifer's ability to remove microbiological contaminants at a test site near Munich, Germany. Test results revealed E. coli relative recoveries could exceed those of H40/1 at monitoring wells, 10 m and 20 m from an injection well, by almost four times; P. putida recoveries varied by a factor of up to three between wells. Application of filtration theory suggested greater attenuation of H40/1 relative to similarly charged E. coli occurred due to differences in microorganism size, while estimated collision efficiencies appeared comparable. By contrast, more positively charged P. putida experienced greater attenuation at one monitoring point, while lower attenuation rates at the second location indicated the influence of geochemical heterogeneity. Test findings proved consistent with observations from nearby fresh outcrops that suggested thin pen framework gravel beds dominated mass transport in the aquifer, while discrete intervals containing stained clasts reflect localized geochemical heterogeneity. Study results highlight the utility of reconciling outcrop observations with artificial tracer test responses, using microbiological tracers with well-defined properties, to characterize aquifer heterogeneity. © 2015 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
Conference Paper
Concentrations of dissolved organic matter (DOM) and ultraviolet absorbance decrease systematically as groundwater moves through the unsaturated zones overlying aquifers and in the saturated zones of aquifers. These changes occur over distances of tens of meters implying rapid removal kinetics of the chromophoric DOM that imparts color to groundwater. A one-compartment input-output model was used to derive a differential equation describing the removal of DOM from the dissolved phase due to the combined effects of biodegradation and sorption. The general solution to the equation was parameterized using a two-year record of dissolved organic carbon (DOC) concentration changes in groundwater at a long-term observation well. Estimated rates of DOM loss from the dissolved phase were rapid and ranged from 0.093 to 0.21 micromoles per liter per day (µM d ⁻¹), and rate constants for DOC removal ranged from 0.0026 to 0.011 per day (d ⁻¹). Applying these removal rate constants to an advective-dispersion model illustrates substantial depletion of chromophoric DOM over flow-path distances of two hundred meters or less and in timeframes of two years or less. These results explain the low to moderate DOC concentrations (20 -75 µM; 0.26 – 1 mg/L) and ultraviolet absorption coefficient values (a 254 < 5 m ⁻¹) observed in older groundwater produced from 59 wells tapping eight different Principal Aquifers of the United States. The nearly uniform optical clarity of groundwater, therefore, results from similarly rapid DOM-removal kinetics exhibited by geologically and hydrologically dissimilar aquifers.
The production and use of engineered nanoparticles (ENPs) inevitably leads to their release into aquatic environments, with the quantities involved expected to increase significantly in the future. Concerns therefore arise over the possibility that ENPs might pose a threat to drinking water supplies. Investigations into the vulnerability of drinking water supplies to ENPs are hampered by the absence of suitable analytical methods that are capable of detecting and quantifiying ENPs in complex aqueous matrices. Analytical data concerning the presence of ENPs in drinking water supplies is therefore scarce. The eventual fate of ENPs in the natural environment and in processes that are important for drinking water production are currently being investigated through laboratory based-experiments and modelling. Although the information obtained from these studies may not, as yet, be sufficient to allow comprehensive assessment of the complete life-cycle of ENPs, it does provide a valuable starting point for predicting the significance of ENPs to drinking water supplies. This review therefore addresses the vulnerability of drinking water supplies to ENPs. The risk of ENPs entering drinking water is discussed and predicted for drinking water produced from groundwater and from surface water. Our evaluation is based on reviewing published data concerning ENP production amounts and release patterns, the occurrence and behavior of ENPs in aquatic systems relevant for drinking water supply and ENP removability in drinking water purification processes. Quantitative predictions are made based on realistic high-input case scenarios. The results of our synthesis of current knowledge suggest that the risk probability of ENPs being present in surface water resources is generally limited, but that particular local conditions may increase the probability of raw water contamination by ENPs. Drinking water extracted from porous media aquifers are not generally considered to be prone to ENP contamination. In karstic aquifers, however, there is an increased probability that if any ENPs enter the groundwater system they will reach the extraction point of a drinking water treatment plant (DWTP). The ability to remove ENPs during water treatment depends on the specific design of the treatment process. In conventional DWTPs with no flocculation step a proportion of ENPs, if present in the raw water, may reach the final drinking water. The use of ultrafiltration techniques improves drinking water safety with respect to ENP contamination.
The Total Organic Carbon (TOC) is an interesting tracer of fast infiltration within karstic systems [3,7]. Regular sampling on several aquifers. from the experimental site of Vaucluse, made it possible to demonstrate the high sensitivity of this tracer compared with other commonly used chemical and isotopic tracers in karstic hydrogeology. The complementarity of magnesium, indicator of the residence time of water within the system, and TOC appears as a relevant tool in order to characterize the behaviour of the aquifer, to differentiate the water types which participate to the karstic flow (fast infiltration, unsaturated zone, saturated zone) and then, to evaluate their vulnerability.
Investigation on factors that affect impact of natural organic matter (NOM) on colloid transport in complex hydraulic flow systems remains incomplete. Using our previously-established approach, interplay of flow rate and particle size on NOM effect was quantified, using flow rates of 1 and 2 ml/min and particle sizes of 50 and 200 nm to represent small nanoparticles (1-100 nm) and large non-nano microspheres (100-1000 nm) in the low-flow groundwater environment. Latex particles, Suwannee River Humic Acid (SRHA) and iron-oxide-coated sand were used as model particles, NOM and aquifer medium, respectively. Quantitative results show NOM blocked more sites for large particles at high flow rate: 1 µg SRHA blocked 5.95×10^9 microsphere deposition sites at 2 ml/min but only 7.38×10^8 nanoparticle deposition sites at 1 ml/min. The particle size effect dominated over flow rate and the overall effect of the two is antagonistic. Granule-scale visualization of the particle packing on the NOM-presented sand surface corroborates the quantification results, revealing more dispersed status of large particles at high flow rate. We interpret this phenomenon as a polydispersivity effect resulting from the differential size of the particles and NOM: high flow and particle size enlarge the ratio of particle-blocked to NOM-blocked areas and thus the NOM blockage. To our knowledge, this is the first model-assisted quantification on the interplay of NOM, flow rate and particle size on colloid transport. These findings are significant for nano-risk assessment and nano-remediation practices.