![pH range, calculated by chemical simulations, for which there is at least 80 % of metal complexed. Chemical simulations were performed assuming the simultaneous presence of one chelating agent (L) at a [L]/ ∑ [M] ratio of 5 ( solid color line ) and 10 ( dashed color line ) and the presence of all metal ions ([Cd]=[Cu]=[Fe]=[Mn]=[P- b]=[Zn]=2×10 − 5 M) with an ex-](https://www.researchgate.net/profile/Isabel-Pinto-2/publication/260271954/figure/fig1/AS:297285188636675@1447889720860/pH-range-calculated-by-chemical-simulations-for-which-there-is-at-least-80-of-metal_Q320.jpg)
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14TH EUCHEMS INTERNATIONAL CONFERENCE ON CHEMISTRY AND THE ENVIRONMENT (ICCE 2013, BARCELONA, JUNE 25 - 28, 2013)
Biodegradable chelating agents for industrial, domestic,
and agricultural applications—a review
Isabel S. S. Pinto &Isabel F. F. Neto &
Helena M. V. M. Soares
Received: 14 September 2013 / Accepted: 23 January 2014 /Published online: 20 February 2014
#Springer-Verlag Berlin Heidelberg 2014
Abstract Aminopolycarboxylates, like ethylenediaminetet-
raacetic acid (EDTA) and diethylenetriaminepentaacetic acid
(DTPA), are chelating agents widely used in several industrial,
agricultural, and domestic applications. However, the fact that
they are not biodegradable leads to the presence of consider-
able amounts in aquatic systems, with serious environmental
consequences. The replacement of these compounds by bio-
degradable alternatives has been the object of study in the last
three decades. This paper reviews the most relevant studies
towards the use of environmentally friendly chelating agents
in a large number of applications: oxidative bleaching, deter-
gents and cleaning compositions, scale prevention and reduc-
tion, remediation of soils, agriculture, electroplating, waste
treatment, and biocides. Nitrilotriacetic acid (NTA),
ethylenediaminedisuccinic acid (EDDS), and iminodisuccinic
acid (IDS) are the most commonly suggested to replace the
nonbiodegradable chelating agents. Depending on the appli-
cation, the requirements for metal complexation might differ.
Metal chelation ability of the most promising compounds
[NTA, EDDS, IDS, methylglycinediacetic acid (MGDA), L-
glutamic acid N,N-diacetic acid (GLDA), ethylenediamine-
N,N′-diglutaric acid (EDDG), ethylenediamine-N,N′-
dimalonic acid (EDDM), 3-hydroxy-2,2-iminodisuccinic acid
(HIDS), 2-hydroxyethyliminodiacetic acid (HEIDA),
pyridine-2,6-dicarboxylic acid (PDA)] with Fe, Mn, Cu, Pb,
Cd, Zn, Ca, and Mg was simulated by computer calculations.
The advantages or disadvantages of each compound for the
most important applications were discussed.
Keywords Chelating agents .Biodegradability .Industry .
Agriculture
Introduction
Chelating agents are widely used in many industrial, domestic,
and agriculture applications due to their ability to complex
metals. Over the last decades, they have been used in several
applications, such as scale and corrosion inhibitors, pulp, paper
and textile production, cleaning and laundry operations,
prevention/inhibition of the growth of microorganisms, soil
remediation, wastes and effluents treatment, agriculture, metal
electroplating and other surface treatments, tanning processes,
cement admixtures, photography, food products, pharmaceuti-
cals, and cosmetics (Knepper 2003; Nowack and VanBriesen
2005). These compounds are mainly used with two different
purposes: (1) to remove critical metals that can affect the effi-
ciency of the process or (2) to avoid metal precipitation and
ensure an essential amount for the good operation of the process.
Among the various chelating agents available,
organophosphonates and aminopolycarboxylates (APCs)
stand out as they are good metal chelators with a good
quality/price ratio. APCs, such as ethylenediaminetetraacetic
acid (EDTA), diethylenetriaminepentaacetic acid (DTPA),
nitrilotriacetic acid (NTA), and also organophosphonates like
diethylenetriamine penta(methylene phosphonic acid)
(DTPMP), hydroxyethylidenediphosphonic acid (HEDP),
and nitrilotrimethylenephosphonic acid (NTMP) are the most
common chelating agents used in the world (Knepper 2003;
Nowack and VanBriesen 2005). In the last decades, discussion
about their environmental consequences has been raised. The
biodegradation of EDTA, DTPA, and organophosphonates is
Responsible editor: Philippe Garrigues
Electronic supplementary material The online version of this article
(doi:10.1007/s11356-014-2592-6) contains supplementary material,
which is available to authorized users.
I. S. S. Pinto :I. F. F. Neto:H. M. V. M. Soares (*)
1REQUIMTE, Departamento de Engenharia Química, Faculdade de
Engenharia, Universidade do Porto, Rua Dr. Roberto Frias,
4200-465 Porto, Portugal
e-mail: hsoares@fe.up.pt
Environ Sci Pollut Res (2014) 21:11893–11906
DOI 10.1007/s11356-014-2592-6
very limited, and they can only be biodegraded in very partic-
ular conditions, with specific isolated bacterial strains (Bucheli-
Witschel and Egli 2001; Nörtemann 2005); still, these com-
pounds do not obey the Organization for Economic Co-
operation and Development (OECD 1992) criteria for biode-
gradability (Knepper 2003). To reduce their concentration in
industrial effluents, additional treatments such as advanced
oxidation processes, which have been reviewed (Sillanpää
and Pirkanniemi 2001; Sillanpää et al. 2011), are necessary.
The understanding of the chemistry of the chelates in
natural waters is essential to predict the fate of these com-
pounds in the environment (Nowack 2002). EDTA is not toxic
for mammals and is used in cosmetics and pharmaceuticals
with no harmful effects in human life (Nowack and
VanBri e s e n 2005), but its strong ability to form metal com-
plexes, together with its persistency in the environment, re-
sults in a perturbation of the natural metal speciation in the
environment. The presence of chelating agents in water solu-
bilizes heavy metals from the sediments and soils, enhancing
its mobility, which can increase the presence of metals in
water supply systems. The exposure of humans, animals,
plants, and microorganisms to heavy metals raises concern
due to their toxic effects. The metal complexes of EDTA
themselves have been found to be more toxic than the free
form of the ligand (Sillanpää and Oikari 1996). Mobilized
metals can include radioactive ions from contaminated soils or
disposal sites, with all the harmful effects associated with
them (Nörtemann 2005). Chelating agents also have an effect
on the liberation of phosphorous due to the dissolution of
metal phosphates that contribute to an increase of microor-
ganisms in water (Oviedo and Rodriguez 2003).
NTA (Fig. 1) was the first chelating agent to be synthesized
and it is widely used. Although it is biodegradable, its usage is
controversial because it is moderately toxic to humans and
mammals and suspected to induce kidney toxicity and tumors
(Bahnemann et al. 1998; Ebina et al. 1986). The present
concentrations of NTA in the environment are lower than the
thresholds determined for these effects (Bucheli-Witschel and
Egli 2001), but its use cannot be increased substantially.
Other biodegradable chelating agents, such as
ethylenediaminedisuccinic acid (EDDS) and iminodisuccinic
acid (IDS), started to be considered and studied as alternatives
in the 1980s, especially to substitute phosphonates in deter-
gents and cleaning compositions, but also in the bleaching
industry and as peroxide stabilizers. EDDS (Fig. 1) can exist
in three stereoisomer forms but only the S,S-isomer is consid-
ered biodegradable according to the OECD guidelines
(Schowanek et al. 1997; Takahashi et al. 1997). Most of the
works concerning the application of EDDS consider the bio-
degradable isomer that will be only identified as EDDS
throughout this work. It is commercialized by Innospec Inc.,
UK as Enviomet
TM
. IDS (Fig. 1), also known as (N-1,2-
dicarboxyethyl)-D,L-aspartic acid, has three stereoisomers as
well, but, unlike EDDS, all of them were proven to be biode-
gradable (Hyvonen et al. 2003). IDS is commercialized by
Lanxess under the name Baypure CX 100, and its synthesis
process is considered environmental-friendly, with no gener-
ation of off-gases or effluents (Kolodynska 2011).
The search for alternative chelating agents, more environ-
mentally friendly, is very important, and several works
concerning the various applications have been published in
the last two decades. The new compounds must be biodegrad-
able, to avoid harmful consequences for the environment, but
also have good chelating abilities and be economically viable.
This is a critical point since most of the biodegradable
complexants have low or moderate stability constants when
compared to EDTA and DTPA. For each application, the
assessment of the best compounds must take into consider-
ation the metals that need (or not) to be complexed, pH range,
and compound characteristics, like solubility and stability in
different conditions, protonation, and stability constants.
Besides EDDS and IDS, there is a group of other APCs
(Fig. 1) that are recurrently mentioned in the literature as
possible substitutes of the traditional chelating agents. The
correlation between the structure and respective biodegrad-
ability has been studied; most of the molecules represented in
Fig. 1have one nitrogen atom, which makes them more easily
biodegraded, while the presence of tertiary amines in EDTA
and DTPA molecules makes them difficult for biodegradation
(Nörtemann 2005).
Methylglycinediacetic acid (MGDA) has a good stability
in a wide pH range and is classified as ready biodegradable
according to OECD (1992) criteria. MGDA commercial name
is Trilon® M and is produced by BASF (2007).
L-Glutamic acid N,N-diacetic acid (GLDA) is classified as
ready biodegradable and has no toxic effect on biotic systems
or human health (Borowiec et al. 2009). This ligand is
marketed on commercial scale by AkzoNobel with the name
Dissolvine® GL-38 (AkzoNobel 2010).
Ethylenediamine-N,N′-diglutaric acid (EDDG) and
ethylenediamine-N,N′-dimalonic acid (EDDM) are two che-
lators, members of the same homologous series of EDDS.
EDDG biodegradability was assessed by Lanham et al.
(2011). Synthesis and biodegradability of EDDM were stud-
ied by Aoki and Hara (2002).
Chelating agent 3-hydroxy-2,2-iminodisuccinic acid
(HIDS) is biodegradable and presents low toxicity (Nippon
2013). The compound is produced and commercialized by
Nippon Shokubai.
2-Hydroxyethyliminodiacetic acid (HEIDA), also com-
monly referred as ethanoldiglycinic acid (EDG), has proven
to be biodegradable (Lynn et al. 1975). Two companies sell
this compound: Dow, as VERSENE™HEIDA, and Akzo
Nobel under the name Dissolvine® EDG.
Pyridine-2,6-dicarboxilic acid (PDA), also known as
dipicolinic acid, contains a pyridine ring and is biodegradable
11894 Environ Sci Pollut Res (2014) 21:11893–11906
according to the OECD guidelines (Martins et al. 2014). It is a
naturally occurring compound, as it constitutes ~10 % of the
dry weigh of Bacillus species spores. Due to its structure, it
tends to chelate metals in a proportion of 2:1 (ligand/metal),
improving the stability of the complex.
Protonation and stability constants (as log β) for several metals
of interest are presented for the APCs mentioned in Table 1.
The present work attempts to give an overview of the
studies where the practical application of biodegradable che-
lating agents was considered and experimented. The biode-
gradability of the chelating agents is not considered funda-
mental in industries like cosmetics, food processing, and
pharmaceuticals, where the compound is used in smaller
quantities. Almost no studies regarding this problematic were
found; therefore, these usages were not object of review in the
present work. Requirements of chelation abilities differ de-
pending on the goal of the application. For the group of
compounds more recurrent in recent literature (EDDG,
EDDM, EDDS, GLDA, HEIDA, HIDS, IDS, MGDA, NTA,
and PDA), computer chemical simulations were performed to
assess their ability to chelate metals, using conditions relevant
for the applications discussed in order to make a standardized
comparison between them.
Applications using biodegradable chelating agents
Oxidative bleaching processes
Chelating agents are widely used in pulp and paper as well as in
textile industries and the current preference for bleaching pro-
cesses free from chlorine (total chlorine-free—TCF) might
increase their usage. TCF bleaching processes are usually based
on oxygen chemicals, e.g., hydrogen peroxide and peroxy
acids. Transition metals, such as Mn, Fe, and Cu catalyze the
decomposition of peroxy compounds, thus its presence in pulp
and cotton affects the efficiency of bleaching and increases
process costs. On the other hand, complexation of Mg must
be minimized because its presence is beneficial for the process.
EDTA and DTPA are the most used chelating agents to control
thepresenceofmetalsandcanbe applied in a pretreatment
stage prior to bleaching or as stabilizers in the actual bleaching
stage. The metals are then removed, as metal complexes, in the
dewatering stage (Ni and Liu 2000),anddischargedintothe
aquatic resources. The quantity of chelant used in the pretreat-
ment stage is usually between 1 and 6 kg/ton of pulp.
EDDS and IDS are the two biodegradable chelating agents
that appear more often associated to pulp bleaching processes.
IDS
EDDM
EDDS
EDDG
GLDA
MGDA
NTA
HEIDA
HIDS
PDA
Fig. 1 Molecular structure of the
biodegradable chelating agents:
nitrilotriacetic acid (NTA),
ethylenediaminedisuccinic acid
(EDDS), iminodisuccinic acid
(IDS), methylglycine diacetic acid
(MGDA), L-Glutamic acid N,N-
diacetic acid (GLDA), 2-
hydroxyethyliminodiacetic acid
(HEIDA), ethylenediamine-N,N′-
dimalonic acid (EDDM),
ethylenediamine-N,N′-diglutaric
acid (EDDG), 3-hydroxy-2,2-
iminodisuccinic acid (HIDS), and
2,6-pyridine dicarboxylic acid
(PDA)
Environ Sci Pollut Res (2014) 21:11893–11906 11895
Tabl e 1 Protonation and overall stability constants of EDTA, NTA, IDS, MGDA, GLDA, EDDG, EDDM, HIDS, HEIDA, and PDAwith Fe, Mn, Cu,
Pb, Cd, Zn, Ca, and Mg ions, at 25 °C, in μ=0.1 M
Reaction EDTA NTA EDDS IDS MGDA GLDA EDDG EDDM HIDS HEIDA PDA
H
+
H+L↔HL 9.5 9.5 10.1 10.0 9.9 9.4 9.5 9.7 9.6
d
8.7 4.7
2H + L ↔H
2
L 15.6 12.0 17.0 14.2 12.4 14.4 16.3 16.3 13.7
d
10.9 6.7
3H + L ↔H
3
L 18.3 13.8 20.8 17.5 13.9 17.9 20.5 19.0 16.8
d
12.5
4H+ L ↔H
4
L 20.3 15.0 23.9 19.4 20.4 3.3 21.1 18.9
d
5H + L ↔H
5
L 21.8 25.3 20.5
d
Fe
3+
M+L↔ML 25.1 16.0 20.1
a
13.9
b
16.5
c
15.2
d
15.7
g
15.0
d
11.6 10.9
M+2L↔ML
2
24.0 17.1
M+H+L↔MHL 26.4 17.0 17.8
b
19.4
d
18.4
d
13.9
M+L↔M(OH)L+H
+
17.7 11.6 12.2
a
8.6
b
-3.3
d
10.0
d
9.2
Mn
2+
M+L↔ML 13.9 7.3 9.0 7.3
b
8.4
c
7.6
e
6.7 8.4 6.8
h
5.5 5.0
M+2L↔ML
2
10.4 9.0 8.5
M+H+L↔MHL 17.0 13.7
M+L↔M(OH)L+H
+
-4.0
b
-3.3
h
Cu
2+
M+L↔ML 18.8 12.7 18.7 12.9
b
13.9
c
13.0
f
15.5 15.9 12.6
f
11.8 9.1
M+2L↔ML
2
17.4 15.8 16.4
M+H+L↔MHL 21.9 14.3 25.0 17.3
b
17.2
f
16.2
f
M+L↔M(OH)L+H
+
7.4 3.5 7.6 2.5
b
3.1
f
3.7
f
3.1 1.6
Pb
2+
M+L↔ML 18.0 11.5 12.7 9.8 12.1
c
11.6
f
8.5 11.1 10.2
f
9.4 8.7
M+2L↔ML
2
11.6
M+H+L↔MHL 20.8 15.0 16.0 16.3
f
14.4 15.3 14.3
f
12.2
M+L↔M(OH)L+H
+
1.0
f
1.2
Cd
2+
M+L↔ML 16.5 9.8 10.9 8.3 10.6
c
10.3
f
8.8 7.6
f
7.4 6.4
M+2L↔ML
2
14.5 12.4 10.9
M+H+L↔MHL 19.4 14.6 13.0 15.0
f
12.7
f
8.8
M+L↔M(OH)L+H
+
3.3 -1.5 0.1
f
-2.6
f
Zn
2+
M+L↔ML 16.5 10.4 13.6
a
10.2
b
10.9
c
11.5
f
10.2 11.1 9.8
f
8.4 6.4
M+2L↔ML
2
14.2 12.0 10.9
M+H+L↔MHL 19.5 17.3
a
14.6
b
16.1
f
13.7
f
M+L↔M(OH)L+H
+
4.9 0.3 2.3
a
-1.1
b
0.9
f
0.8
f
-1.1
Ca
2+
M+L↔ML 10.7 6.3 4.6 4.3 7.0
c
5.9
e
2.6 5.4 4.8
i
4.7 4.4
M+2L↔ML
2
8.8 7.4
M+H+L↔MHL 12.8 11.5 3.6 11.7
M+L↔M(OH)L+H
+
Mg
2+
M+L↔ML 8.8 5.5 6.0 5.5 5.8
c
5.2
e
3.0 4.9 3.4 2.3
M+2L↔ML
2
3.0
M+H+L↔MHL 12.8 11.9 4.3 11.5
M+L↔M(OH)L+H
+
Values from NIST Database (Martell and Smith 2004) unless otherwise indicated
a
Orama et al. 2002
b
Hyvonen et al. 2003
c
BASF 2007
d
Begum et al. 2012a
e
AkzoNobel 2010
f
Begum et al. 2012b
g
Tak e t al. 1971
h
Hyvonen and Aksela 2010
i
Nippon 2013
11896 Environ Sci Pollut Res (2014) 21:11893–11906
Renvall et al. (1997) and Chauveheid et al. (1999)suggesta
general formula for chelating agents to be applied in the
pretreatment of the pulp and both EDDS and IDS are in
accordance with the formula proposed. Employing a chelant
dose of 2 kg/ton of pulp, Mn concentration in the filtrate was
3.0 ppm using EDDS at optimum pH (6.5–7.0), which was
10 % below the value obtained for EDTA and DTPA (Renvall
et al. 1997). For Fe, similar results were obtained for EDDS,
EDTA, and DTPA, with metal concentrations of 2.0 ppm in
the filtrate. For both metals, when IDS was used, the removal
was 50 % below the traditional chelants. After the bleaching
step, no significant differences were found for brightness;
however, hydrogen peroxide consumption was usually lower
for DTPA. Experiments for stabilization of hydrogen peroxide
showed that in the presence of EDDS and IDS, the peroxide
was mostly degraded in the first 15 and 60 min, respectively,
but in the presence of EDTA or DTPA, it was still stable after
90 min.
Jones and Williams (2001) focused on the problem of
finding biodegradable alternatives in the pulp and paper in-
dustry, through computer chemical simulations. The lower
affinity of EDDS and IDS for Ca makes them promising
alternatives for replacing EDTA.
Giles and Dixon (2009) proposed a bleaching pretreatment,
at pH 4–7.5 with a mixture of biodegradable and nonbiode-
gradable chelating agents. According to this work, the mixture
of chelating agents resulted in a better brightness than it would
be expected from the results using similar amounts of each
chelating agent alone. For instance, DTPA and EDDS, when
used alone under the same experimental conditions, resulted
in a brightness of 66.0 and 63.9, respectively, after the perox-
ide stage. When applied together in a ratio of 30:70, the
obtained brightness was 66.9. The biodegradable com-
pounds suggested are EDDS, MGDA, GLDA, and IDS
and can be combined with DTPA, EDTA, or DTPMP.
Even though these formulations still contain nonbiode-
gradable chelating agents, the combination of both types
of chelants can be a solution for obtaining good chelat-
ing and bleaching results combined with a more envi-
ronmentally friendly process since lower amounts of
nonbiodegradable chelating agents are used.
Recently, PDA and MGDA were tested experimentally
in a pretreatment of paper pulp, at pH 5–7(Pintoetal.
2014). In these experiments, a consistency of 70 kg of
dried pulp/m
3
,followedbyableachingsequencewith
hydrogen peroxide and peracetic acid, was used. Mn
was totally removed from the pulp with both ligands
studied and EDTA, but MGDA at 3.7×10
−3
Malsosolu-
bilized up to 70 % of Mg. On the other hand, PDA at
2.0×10
−3
M was more selective and a removal of only
37 % of Mg was achieved. Similarly, NTA (7.0×10
−4
M)
and EDDM (4.5×10
−4
M) removed Mn efficiently with a
good selectivity over Mg (Neto et al. 2014).
Detergents and cleaning compositions
Chelating agents found in detergents, both used for laundry or
dishwashing, are frequently added to the composition to soft-
en water by inactivating Ca and Mg ions, which are the major
metal ions that contribute to hardness. Hard water has negative
effects in cleaning applications due to precipitation of min-
erals that accumulate in the washing machines or in other
objects. Chelating components inactivate Ca and Mg ions by
sequestration, leaving them soluble. Phosphonates have been
extensively used in detergents, but they pose some environ-
mental concerns. There are also cases where compounds are
added to laundry detergents with peroxy-based bleaching
agents to chelate heavy metals in order to stabilize the solution
(Baillely et al. 1994).
The target metal ions must be complexed between pH 7
and 12, which is the typical pH of cleaning and washing
operations. Considering the large quantity of chelating agents
used in cleaning compositions, which can be up to 30 wt.%,
this is a crucial application where biodegradable alternative
chelating agents should be used.
PDA was added as a builder in dishwashing (De Ridder
1983; Frankena 1988) and laundry (Boskamp 1990)compo-
sitions due to its ability to sequester Ca ions. In the experi-
ments performed by De Ridder (1983), the capacity of se-
questering Ca, using 0.15 g/L of chelating agent, was mea-
sured by weighting the insoluble Ca deposit in glass slides.
EDTA and NTA had better performances with formation of
4.1 and 3.6 mg of solid deposit, respectively. PDA was also
effective (formation of 4.5 mg of deposit) when compared to
the situation where no chelating agent was used (7.4 mg of
deposit). These results could still be improvedby changing the
concentration of other components in the detergent. The ad-
dition of 2.0 % of PDA in a laundry detergent had a significant
effect on avoiding the reduction of the fabrics reflectance after
10 washes (Boskamp 1990).
In recent years, MGDA and GLDA studies in cleaning
applications became more frequent. MGDA alone showed a
good ability to inhibit scale formation due to calcium or
magnesium carbonate precipitation (Dailey et al. 2011).
When different compositions of the builder were tried, it was
verified that this parameter can be more or less affected
depending on the compounds and quantities present. MGDA
or GLDA can be present in a detergent composition together
with citrate and carbonate. Citrates are weaker chelants, but
mixed with a stronger chelating agent, can also sequester
hardness metals as they act as an alkaline buffer (Jefferis and
Zack 2011).
Another purpose for the addition of chelating agents to
cleaning compositions is to chelate heavy metal ions (Fe,
Mn, Cu) present in stains to enhance their removal (Palladini
2007;Pike1996). Palladini (2007) suggested detergent for-
mulations containing one biodegradable chelating agent (IDS
Environ Sci Pollut Res (2014) 21:11893–11906 11897
or GLDA) pointing out the importance of both sequestration
of hardness and heavy metal ions.
ThepresenceofEDDSandEDTAinalaundrydetergent
composition at two concentrations (3.3 and 6.7 %) was studied
for the removal of organic stains at pH 9.8 (Hartman and
Perkins 1987). For some types of stains, the addition of chelant
does not make any difference; grape juice and tea were better
removed in the presence of EDDS while grass and bacon
removal was higher with EDTA. In general, higher concentra-
tion of chelating agent led to better removal of the stains.
For the rinse aid composition, proposed by Pike (1996), the
compounds must chelate heavy metals, preferentially at pH
lower than 7 to improve the removal of stains. In fact, these
pH conditions usually enhance bonding with heavy metals
instead of Ca and Mg for the majority of the chelating agents.
EDDG and hydroxypropylenediamine disuccinic acid
(HPDDS) were used, but since the purpose of using chelants
was the complexation with heavy metals during the rinsing
cycle of the dishwasher, phosphonates were also present to
soften water.
HEIDA salts have been compared to EDTA salts in a
composition with 3.2 % of chelating agent for hard surface
cleaning (Crump and Wilson 2011). The cleaning of soiled
tiles, where the soil contained Fe, Ca, and Mg was measured
by the number of strokes necessary to remove 90 % of the soil.
Even though HEIDA stability constants are significantly low-
er, HEIDA and EDTA potassium salts showed similar
cleaning efficiency (with 19 strokes each).
The use of HEIDA was also proposed by Giles and Dixon
(2012) in a dishwashing composition mostly free of bleaching
agents and phosphate builders. A second chelating agent,
biodegradable or not, could be added maintaining the total
concentration at 15 %. Compositions with mixtures of chelat-
ing agents gave better results on the removal of tea stains than
compositions with just one chelating agent, with an increase
of the cleaning score value up to 30 %.
Scale prevention and removal
The hardness ions present in the water used in industrial
processes lead to the formation of scale in metallic surfaces
of equipments, especially in heat exchanging processes. These
incrustations decrease the efficiency of heat transmission,
increase pressure drop, and promote the corrosion of the
equipment (Simpson et al. 1999). The removal of these de-
posits can be very costly, time consuming, and harmful to the
environment due to the use of strong acids and alkalis (Zack
et al. 2012). Chelating agent solutions can be used to prevent
and/or remove scale from the equipments.
In circulating aqueous systems for steam generating and
cooling, chelating agents can be added to the water. The
stability of GLDA (at 13 % in the treatment solution) and
EDDS (at 9.3 % in the treatment solution) and their ability to
avoid metals precipitation were tested at high temperatures
(216–235 °C) and pressures (21–31 bar) to assess their use in
water systems (Charkhutian et al. 2004,2006). The stability of
both compounds decreases for higher temperatures and pres-
sures. The anti-precipitation effect was tested, at pH 10, for
Ca, Mg, and Fe separately and with the three metals together.
When the three cations were mixed and tested at 216 °C and
21 bar, the results were similar between both ligands, with
more than 80 % of Mg and Ca and around 50 % of Fe
remaining in solution instead of precipitating. GLDA showed
better results for the solutions containing only one metal,
especially for Mg and Fe, while Ca showed a good stability
in solution with both compounds.
Aqueous solutions containing biodegradable chelating
components, such as MGDA and GLDA, can be used as oil
field chemicals. In this case, the solutions are preferentially
acidic or neutral and the main goal is to dissolve calcium
carbonate scale and other subterranean carbonate formations
to increase permeability and enhance the withdrawal of oil or
gas (De Wolf et al. 2009,2012). In the case of very acidic
solutions, GLDA showed a better solubility in aqueous acids
than other chelants.
For control and removal of Ca and Mg deposits at alkaline
pH in a steam generator, NTA and EDDS were suggested as
biodegradable alternatives, along with some nonbiodegrad-
able compounds (Richardson et al. 2012). Zack et al. (2012)
tested MGDA at pH close to neutrality, with the addition of
different acids, to dissolve calcium carbonate. In the presence
of methanesulfonic acid, the increase of MGDA concentration
from 0 to 8.7 % improved the scale dissolving capacity from
26.6 to 43.7 %.
The formation of Ca scale is also a major problem in the
pulp and paper industry, both in pulping and bleaching stages.
The presence of Ca in alkaline bleaching stage can lead to
precipitates, mainly oxalate and carbonate that accumulate in
the equipment, forming scale that is hard to remove. The
presence of chelating/sequestering agents, such as EDTA
and DTPA, can help to increase the solubility of calcium
oxalate (Elsander et al. 2000; Moore et al. 2012).
Biodegradable alternatives must be good Ca chelators forming
soluble and stable complexes. Pinto et al. (2014) considers
PDA as a possible Ca chelator to prevent the formation of
scale during pulp bleaching, since about 90 % of the Ca
present in the pulp is removed during the pretreatment.
Remediation of soils
The presence of toxic metals in the soils has become a
major concern due to industrial and agricultural practices,
inappropriate waste disposal, and increasing urbanization.
Heavy metals cannot be mineralized or decomposed; there-
fore, human intervention is needed to remove them from
the soils.
11898 Environ Sci Pollut Res (2014) 21:11893–11906
Soil washing and flushing
In situ and ex situ remediation techniques have been studied
(Lestan et al. 2008), and chelating agents can be applied in
both techniques. In situ techniques include phytoremediation
and soil flushing. Ex situ methods usually consist of soil
washing to separate contaminants and the use of chelating
agents is less disruptive for the soils than acid washing.
According to some authors, the chelating agents must have
low biodegradability to allow recycling and reuse of the
washing solution (Dermont et al. 2008;Lestanetal.2008),
thus reducing treatment costs. Nevertheless, a fast biodegra-
dation rate of the ligand in this application is not convenient
because removal of metals from the soil cannot occur or be
inefficient. EDDS biodegradation studies in soils showed a lag
phase up to 11 days and proved that degradation was effective
even in polluted soils (Tandy et al. 2006). Meers et al. (2008)
compared the biodegradability of EDDS in three different
soils and concluded that the time of degradation differed
significantly due to different durations of the lag phase. The
type of soil is important in biodegradation and can be related
to EDDS recovery and reuse in remediation of soils.
Chelants must also have low toxicity to soil microorgan-
isms, which is not observed for EDTA (Epelde et al. 2008;
Kos and Lestan 2003), and the metal complexes should not
adsorb on the solid surfaces (Dermont et al. 2008). The ligand/
metals ratio must be higher than 1, to maximize the metals
removal, especially due to interferences of other cations pres-
ent in the soil (Fe, Mn, Ca, Al and Mg). The low selectivity of
EDTA caused by strong chelation with interfering cations is a
disadvantage in this process (Dermont et al. 2008).
In the middle 90s, PDA was considered for soil remediation
applications (Pb and Cd extraction and recovery), although it
was not mentioned as a biodegradable alternative in the respec-
tive studies (Macauley and Hong 1995; Hong and Chen 1996).
The extraction of Pb from soil with PDA 1 mM was above
80 % in four consecutive experiments using reused PDA
(Macauley and Hong 1995). Efficiency of extraction was com-
parable to EDTA, but PDA has the advantage of forming
weaker chelates, which makes the release of extracted Pb easier.
Heavy metals extraction from soils was studied using an ex
situ washing procedure (Vandevivere et al. 2001). EDDS
achieved extraction efficiencies of Pb, Zn, Cu, and Cd be-
tween 70 and 90 % as long as the contact time was sufficient
(1 to 6 days, depending on the metal) and pH higher than 7 in
order to avoid Fe interference.
Tan dy e t al. (2004) studied EDDS, NTA, IDS, and MGDA
for the extraction of Cu, Zn, and Pb and verified that the best
time for the experiments was 24 h; longer times only enhanced
Fe extraction without improving the other metals efficiency.
Although extractions of Cu and Pb were better using EDTA
(values above 80 % of extraction), EDDS, at pH 7, was
considered the best compromise between extraction of Cu,
Zn, and Pb (>60 % at chelant/metal=10) with reduced loss of
Ca and Fe.
Studies performed by Polettini et al. (2006) were focused on
the efficiency of the extraction of Cd, Cu, Pb, and Zn from soils
using different treatment durations. NTA, citric acid, and
EDDS were compared with EDTA. EDDS showed extraction
efficiency of target metals comparable to EDTA. EDDS also
had the advantage of reducing the co-extraction of metals from
the soil matrix, like Ca, Mg, and Fe to values below 10 %.
Yang et al. (2012) concluded that pH 5.5 led to better
extraction than pH 8.0, using EDDS, especially for Zn (64.4
vs. 53.3 % at 1.26 mol EDDS/kg soil) and Cd (52.2 vs.
37.2 %). These conclusions are contrary to the work of
Vandevivere et al. (2001), where pH above 7 evidenced better
results. These facts suggest that the optimal pH is dependent
of soil characteristics, namely the quantity of interfering metal
cations and the way how metals are coordinated to the soil.
Comparison between batch and column experiments on the
efficiency of EDDS for extracting Cu, Zn, and Pb showed that
Zn and Pb are equally extracted while Cu was affected in
column leaching (Hauser et al. 2005). The importance of
performing experiments in column is that this method is more
practical and economical to upscale. It was observed that
short-time experiments were more adequate for EDDS to
maximize the recovery and reuse of the ligand because longer
processing led to loss of compound due to biodegradation. For
simulating an in situ soil flushing situation, Mancini et al.
(2011) used column tests, comparing EDDS with EDTA for
Pb, Cu, Ni, Cd, and Zn mobilization. EDDS presented a better
mobilization capacity for Cu, Ni, and Zn, while EDTA gave
better results for Cd and Pb.
Several chelants (EDDS, IDS, MGDA, GLDA, and HIDS)
in 0.05 M solutions were compared in the treatment of a soil
(1:10 w/v) contaminated with Cd, Cu, Ni, Pb, and Zn at pH 4,
7, and 10 (Begum et al. 2012c). In general, extractions were
enhanced at pH 4. At this pH, the metal extraction perfor-
mance of GLDA for all metals studied was better (Cd 84 %,
Cu 94 %, Pb 54 %, Zn 62 %, and Ni 39 %) than for the other
biodegradable options and even better than EDTA for Ni and
Cu. At pH 7, metal extraction efficiencies decreased but
GLDA was still the best biodegradable option. These results
cannot be explained by the stability constants of the metal
complexes but probably by the way how metals are coordi-
nated to the soil. In order to guarantee homogeneous condi-
tions in the study, the same research group compared EDDS,
GLDA, and HIDS with EDTA on the treatment of artificially
contaminated reference soils (Begum et al. 2013). Chelant/
metal molar ratio and solution pH were varied, and results
showed that GLDA had the better extraction efficiency for the
lower chelant concentration (0.01 M). A better performance of
GLDA than EDTA was obtained, at pH 4, except for Pb,
which is consistent with a previous work of the same authors
(Begum et al. 2012c). At higher pH, EDDS performance is
Environ Sci Pollut Res (2014) 21:11893–11906 11899
better than GLDA but none of the biodegradable chelating
agents is able to achieve the same efficiency as EDTA on the
extraction of Pb.
Phytoremediation
Plants have the ability to uptake metals that have no biological
function (Rahman et al. 2011). Since the remediation of large
areas by soil washing can be very costly, the use of plants to
accumulate heavy metals arises as a possible solution to
extract contaminants and restore the fertility of the soil. The
metals must be uptaken from the soil, transported from roots
to shoots, and accumulated in aboveground parts of the plants
(Rahman et al. 2011). After harvesting, the plants are burned
to produce energy and metals are recycled from the residues
(Kos and Lestan 2003). Chelating agents are used to increase
the solubility and mobilization of the metals, making them
bioavailable for plants (Nowack and VanBriesen 2005). The
main concern of using nonbiodegradable chelating agents is
their persistence in the soils that leads to the leaching of heavy
metals into underground waters.
EDDS has been the most studied alternative for EDTA in
phytoextraction. Studies performed with EDDS by Kos and
Lestan (2003), Luo et al. (2005), Epelde et al. (2008), and
Evangelou et al. (2007) for different plant species showed that
EDDS is more efficient than EDTA for Cu and Zn uptake but
less efficient for Pb. However, plant growth was affected by
EDDS, evidencing some toxicity. EDDS toxic effects were
not observed in other studies (Komarek et al. 2010;Meers
et al. 2005), which means that EDDS toxicity is dependent on
plant species and experimental conditions, such as, pH, type
of soil, presence of other metals, etc. The study performed by
Meers et al. (2005) also showed that metals mobilization
decreased with time when EDDS was used. This behavior
was not observed for EDTA and can be explained by the
higher biodegradability of EDDS.
Shilev et al. (2007) studied NTA and EDDS to enhance the
accumulation of Cd, Pb, and Zn in maize and sunflower. The
results revealed that the efficiency depends on the plant spe-
cies. For instance, Cd was more efficiently accumulated in the
leaves of sunflower in the presence of NTA (5 mmol/L) and
EDDS was better for maize. In addition, no negative effects in
soil bacteria and fungi were observed, which is an advantage
over EDTA. Freitas and Nascimento (2009) and Araújo and
Nascimento (2010) concluded that NTA toxicity to the plants
was significant but lower than EDTA, while Pb leaching
results showed that NTA caused no environmental effects,
unlike EDTA (Araújo and Nascimento 2010).
Cao et al. (2007) compared Pb and Zn phytoextraction by
ornamental flowers using EDDS and MGDA in dosages of 4
and 8 mmol/kg of soil. Both of the ligands showed an effective
increase in Pb accumulation in leaves as well as a benefic
contribution for bacterial activity in the soil. In the case of Zn,
metal accumulation was independent from the use of chelating
agents. EDDS and MGDA showed some toxicity to the plant
causing death at maximum dose. The application of MGDA to
a primrose species showed an effective Cu extractions and
increase in foliar concentration and plant growth (González
et al. 2011).
Iron-chelating agents for agriculture
Iron is an important nutrient for plant growth, and its deficien-
cy is one of the causes of chlorosis in plants. Chlorosis leads to
loss in the fruit quality and yield, lack of the green color in the
leaves, and in extreme cases, the death of the plant
(Rodriguez-Lucena et al. 2010). The deficiency of Fe in plants
is caused by Fe poor bioavailability, especially in calcareous
soils (Shenker and Chen 2005). Above pH 7, Fe species are
mainly insoluble and cannot be taken by the plants; thus,
chelating agents can be added to the soil in order to make
the Fe already present bioavailable or supplied to the plant as
Fe-chelates in fertilizers solutions (Lucena et al. 2008; Villen
et al. 2007). EDTA and DTPA complexes are often used in
liquid formulations; however, for calcareous soils,
ethylenediamine-N,N′-bis(1-hydroxyphenylacetic) acid
(EDDHA) is the most used because of its even higher stability
constant of the FeL complex, which allows complexation at
higher pH (Lopez-Rayo et al. 2009; Shenker and Chen 2005).
The use of IDS chelates (Fe, Mn, Zn and Cu) in fertigation
and hydroponics formulations resulted in healthy plants
(Lucena et al. 2008). The same compound was tested in a
foliar spray composition though this technique was not as
effective.
The ability of the chelating agents to improve the mobility
of Fe in the soil is important to increase the bioavailability of
Fe for a plant. HIDS and EDDS showed a higher apparent
mobility followed by GLDA, EDTA, MGDA, and IDS at
pH 10 (Hasegawa et al. 2011). Results were related to the
growth of radish sprouts that showed the same trend. Authors
claim that stability constant of the FeL complex influences the
movement of Fe in the growth medium but the stability
constants in Table 1do not show the same trend.
At pH< 7 and 0.25 M of chelant, HIDS was more efficient
on the Fe uptake and plant growth than EDTA, EDDS, and
IDS (Rahman et al. 2009). HIDS is considered an effective
option to replace nonbiodegradable chelating agents in agri-
culture and Fe uptake due to the good experimental results as
an iron chelator and plant growth and its stability in severe
conditions (Hasegawa et al. 2011). The very fast biodegrada-
tion is also shown as an advantage by some authors
(Hasegawa et al. 2011,2012). However, this property can be
seen as a disadvantage for agricultural purposes since the
ligand should have some resistance to degradation in order
to increase the period of action of fertilizers and fulfill its
purpose as metal chelating agent (Shenker and Chen 2005).
11900 Environ Sci Pollut Res (2014) 21:11893–11906
EDDS was compared with DTPA and EDTA as a Fe-
chelate source in a liquid fertilizer for the production of
marigold and extractant of metals from peat medium. Plants
treated with Fe-EDDS solution showed enough Fe in the
leaves for a normal growth (Albano 2008).
Other applications
Electroplating Electroless deposition of Cu into metallic sur-
faces can be done in the presence of complexing agents to
stabilize the metallic ions in solution by avoiding its precipi-
tation as metal hydroxide in the alkaline baths. The most
common complexants used in plating industry are EDTA
and tartrate salts. Performance of biodegradable chelating
agents, such as EDDS and NTA, has been also tested in
electroplating of Cu (Macmillan 1996; Pauliukaite et al.
2006; Simpson et al. 1999; Wilson and Crump 1994). The
stability of the electroless plating solution containing EDDS
was comparable to the situation where EDTA was used and
the rate of Cu deposition was very favorable (Macmillan
1996). From this study, it could be concluded that the use of
EDDS fulfilled the requirements for the industry and can
replace EDTA in existing plating systems.
Wast e t re atm e nt Sewage sludge can be recycled as fertilizer
for land because of its large content of organic substances and
also nitrogen and phosphorus content. However, the toxicity
of the heavy metals present in the sewage is a risk to human
health and plants (Zhang and Zhang 2012). Heavy metals in
sewage sludge can be removed by chelating agents, before its
reuse as a fertilizer. Zhang et al. (2008) and Zhang and Zhang
(2012) studied the use of EDDS to extract Cu and Zn from
sewage sludge. Zhang et al. (2008) observed that, within the
pH range of 4–10, both EDDS and EDTA had a good and
equivalent performance for extracting Cu from the sewage
sludge. Zhang and Zhang (2012) showed that the extraction
efficiency of Zn, using EDDS, was comparable to the extrac-
tion efficiency obtained with EDTA at pH between 5 and 9.
Spent hydrodesulphurization catalysts, used in petroleum
refineries, contain metals that must be extracted and recycled
to avoid their deposition in the environment. This is common-
ly done by acid or alkaline leaching but EDTA has also been
used (Goel et al. 2009; Pinto and Soares 2013). EDDS
(Chauhan et al. 2012) and NTA (Pinto and Soares 2013)have
been studied in the removal of Mo and Ni from these catalysts;
however, the metal recoveries were not as high as with EDTA
due to the lower stability constants of these ligands.
Indium is a rare metal employed in the fabrication process
of liquid crystal display (LCD) panels. The quantity of spent
LCD panels is increasing worldwide and they can be a sec-
ondary source of indium (Hasegawa et al. 2013a,b).
Hasegawa et al. (2013a) studied the use of NTA, IDS, and
HIDS to extract indium from spent LCD. NTA showed to be
comparable with EDTA at optimal conditions (acidic medium,
temperature ≥120 °C, and the pressure of 50 bar).
Biocides Some specific metal ions possess biocidal properties
and can be used for stabilization, inhibition, or reduction of the
growth of microorganisms when associated to a chelating
agent (Borkow et al. 2010). Several formulations containing
various biodegradable chelating agents, such as citric acid,
salicylic acid, NTA, EDDS, MGDA, and GLDA, have been
reported in the literature for cleaning and disinfection (Back
et al. 2003; Ploumen and Borgmann-Strahsen 1991; Romano
et al. 2000), herbicidal, fungicidal, or algaecide purposes
(Samarajeewa and Taylor 2011). Back et al. (2001) described
a method to control microbial growth in the water of climate
control systems where salicylic acid and NTA were found to
be effective.
Assessment of potential application of chelating agents
by computer calculations
In order to better understand the ability of the biodegradable
chelating agents for the applications described in this review,
computer simulations were performed and major conclusions
are pointed out in Figs. 2and 3and in the supplementary data
found in online resources 1and 2. For assessing the potential
of each chelating agent for a specific application, the target
metals to be chelated and the pH range should be considered
in the computer simulations. Briefly:
1) In paper pulp and textile TCF bleaching processes, there
is a need to form strong complexes of Fe, Mn, and Cu
while leaving Ca and especially Mg uncomplexed. In the
case of a pretreatment process before bleaching, the pH
range might vary between 4 and 8. Additionally, during
the bleaching stage, chelants are also useful in the stabi-
lization of the peroxide solution itself; this process is
typically performed between pH 9 and 12.
2) To avoid scale formation in industrial cooling or heating
systems, as well as for using in the detergents, it is
important to complex Ca and Mg ions between pH 6
and 12.
3) The remediation of metal-polluted soils implies the solu-
bilization of contaminant metals, usually Pb, Cd, Cu, and
Zn, while reducing the extraction of cations that are
important for plant growth and soil quality (Fe, Mn, Ca,
and Mg). In ex situ remediation, pH might be varied
between 4 and 10 while for phytoremediation, a narrower
interval is preferred (6–8).
4) In the case of agricultural practices, the main goal is to
increase Fe uptake by plants mainly in calcareous soils;
so, ligands must complex Fe to enhance its mobility at pH
higher than 7.
Environ Sci Pollut Res (2014) 21:11893–11906 11901
According to the aims to be fulfilled when chelating agents
are used in these major applications, two different computer
simulations were performed. In the first case, the selectivity of
each chelating agent to transition metals in medium with
Fig. 2 pH range, calculated by
chemical simulations, for which
there is at least 80 % of metal
complexed. Chemical simulations
were performed assuming the
simultaneous presence of one
chelating agent (L) at a [L]/∑[M]
ratio of 5 (solid color line)and10
(dashed color line) and the pres-
ence of all metal ions
([Cd]=[Cu]=[Fe]=[Mn]= [P-
b]= [Zn]=2×10
−5
M) with an ex-
cess of Ca and Mg ions
([Ca]=[Mg]=1 ×10
−3
M)
0
20
40
60
80
100
0
20
40
60
80
100
0 2 4 6 8 10 12 1402468101214
pH
% Complexed Metal
ba
Fig. 3 Amount, in percentage, of Ca (a) and Mg (b)complexedwith
NTA (yellow), EDDS (gray), IDS (pink), MGDA (green), GLDA
(orange), EDDG (blue), EDDM (brown), HIDS (violet), HEIDA (light
blue), PDA (red) and EDTA (black). Chemical simulation were per-
formed assuming the simultaneous presence of Ca, Mg and each chelat-
ing agent, with a [L]/([Ca] + [Mg]) ratio of 2, [Ca]= [Mg]=1×10
−3
M
11902 Environ Sci Pollut Res (2014) 21:11893–11906
excess of Ca and Mg ions was evaluated. In the second case,
the ability of compounds to complex Ca and Mg ions at a high
concentration was assessed. Metal chemical speciation calcu-
lations were performed using MINEQL+ Version 4.5
(Schecher and McAvoy 2003), a computer program that gen-
erates chemical equilibrium concentrations of all species be-
ing considered in the model by the program reactions.
Computational simulations were performed in aqueous medi-
um in the pH range between 0 and 14 and the studied chelating
agents were EDDS, EDDG, EDDM, EDTA, GLDA, HEIDA,
HIDS, IDS, MGDA, NTA, and PDA. The first simulation was
performed in the presence of all transition metals (M–Fe, Mn,
Cu, Pb, Cd, and Zn), and one chelating agent (L), in a situation
of excess of Ca and Mg ions. Two different conditions were
tested, [L]:∑[M] ratios of 5 and 10 with [M]=2×10
−5
Mfor
each transition metal, except Ca and Mg. The concentration of
Ca and Mg ions was 1× 10
−3
M for each metal ion.
In the second simulation, the presence of Ca and Mg with
one chelating agent was assessed. The concentration of che-
lating agent was twice the sum of Ca and Mg ions, [L]=
2([Ca]+[Mg]), where [Ca]= [Mg]=1×10
−3
M. The main re-
sults taken from the first and second computer simulations are
represented in Figs. 2and 3,respectively.
Figure 2shows the pH range at which the chelating agent
complexes more than 80 % of the respective transition metal
(Fe, Mn, Cu, Pb, Cd, and Zn) in a medium with Ca and Mg in
excess. The results for EDTA are also shown to allow an easy
comparison with the most usual situation. Despite the good
ability of all compounds to complex transition metals, EDTA
chelates most metals in a larger pH range, especially Fe, Mn,
and Pb.
For paper pulp and textile bleaching process, considering
only the pH range and the metals to be chelated, we can
conclude that NTA, EDDS, MGDA, and PDA could be used,
which is in line with the literature (Chauveheid et al. 1999;
Moore et al; 1997;Netoetal.2014; Pinto et al. 2014; Renvall
et al. 1997; Seccombe and Dournel 2007). For EDDM, al-
though stability constants for Fe were not found, a recent
study showed that this compound could be a potential alter-
native to this process (Neto et al. 2014). As Giles and Dixon
(2009) suggested, a mixture of biodegradable and nonbiode-
gradable chelating agents can be an interesting option. The
combination of GLDA, IDS, or HIDS with EDTA can over-
ride the lack of affinity of GLDA, IDS, and HIDS to Fe ions.
In soil remediation process, NTA and EDDS could be used;
however, these ligands can only be used at alkaline pH to
avoid the removal of Fe, as it was mentioned by Vandevivere
et al. (2001)andTandyetal.(2004). Also IDS, HIDS,
HEIDA, PDA, MGDA, EDDG, and GLDA could be used
and experimental studies have already been performed
(Arwidsson et al. 2010; Begum et al. 2012c,2013; Cao et al.
2007; Macauley and Hong 1995; Tandy et al. 2004). The
conclusion obtained from these studies is that none of the
biodegradable options has a good performance for removing
Pb as EDTA. This fact is justified by the evident stronger
ability of EDTA to complex this metal.
According to the speciation simulations, only NTA could
be an interesting option to increase Fe bioavailability in agri-
culture using the higher [L]:[M] ratio simulated. Despite the
poor chelation ability evidenced by the computer simulations,
different researchers described that some of these chelating
agents could be possible options (Albano 2008;Hasegawa
et al. 2011,2012;Lucenaetal.2008).
Figure 3shows the percentage of Ca (Fig. 3a)andMg
(Fig. 3b) complexed over the pH range in a solution with only
Ca and Mg and one chelating agent. These simulations were
performed in order to understand the possibility of using the
chelating agents to avoid scale formation or to be applied in
detergents. The computer simulations suggest better results
with the use of NTA, MGDA, and GLDA. Both MGDA and
GLDA are frequently suggested in the literature for these
applications due to their high potential to complex with Mg
and Ca ions (Charkhutian et al. 2004,2006;DeWolfetal.
2009; Palladini 2007;Zacketal.2012). PDA and HEIDA
couldalsobeusedwhenonlyCaionscomplexationis
required.
Conclusions
The search for more environmentally friendly chelating agents
to replace traditional EDTA and DTPA resulted in numerous
studies in the last two decades. Most of the research regards
areas where there is a large consumption of chelating agents,
such as paper pulp bleaching, detergents and cleaning, scale
prevention, soils remediation, and agriculture.
Many biodegradable compounds, like NTA, EDDS, IDS,
MGDA, GLDA, EDDG, EDDM, HIDS, HEIDA, and PDA,
have been suggested as potential alternatives and some of
them are now marketed to be used at industrial scale. EDDS
has been widely studied in different applications and, in some
cases (e. g. detergents), used at commercial scale. In the last
decade, the various papers and patents, where MGDA and
GLDA were studied, pointed out the use of these compounds
as biodegradable substitutes in main industries.
Computer simulations, based on stability constants of
complex formation, show the difficulty of finding an alter-
native biodegradable compound with chelation ability as
good as EDTA. However, the requirements depend on the
purpose and, in some cases, a more selective chelation is
preferred, which can be an advantage for the biodegradable
options.
With the aim of replacing nonbiodegradable chelating
agents in industrial and agriculture applications, the need to
find efficient and low-cost alternatives and optimize processes
still remains.
Environ Sci Pollut Res (2014) 21:11893–11906 11903
Acknowledgments This work was financially supported by FEDER
funds through the Programa Operacional Factores de Competitividade –
COMPETE and national funds by FCT-Fundação para a Ciência e
Tecnologia within the project PTDC-AAC-AMB-111206-2009. One of
us (Isabel F.F. Neto) acknowledges a grant scholarship financed by the
same project, PTDC-AAC-AMB-111206-2009.
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