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Emerging Organic Contaminants in Groundwater
Chapter · January 2013
DOI: 10.1007/978-3-642-37006-9_12
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Marianne Stuart
Dan J Lapworth
British Geological Survey
British Geological Survey, Wallingford
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Emerging Organic Contaminants in
Groundwater
Marianne Stuart and Dan Lapworth
British Geological Survey, Wallingford, OX10 8BB UK
*Email: [email protected]
Abstract
Emerging organic contaminants (ECs) are compounds now being found in
groundwater from agricultural, urban sources that were previously not detectable, or
thought to be significant. ECs include pesticides and degradates, pharmaceuticals,
industrial compounds, personal care products, fragrances, water treatment byproducts, flame retardants and surfactants, as well as ‘life-style’ compounds such as
caffeine and nicotine. ECs may have adverse effects on aquatic ecosystems and
human health.
Frequently detected ECs include the anti-epileptic drug
carbamazepine, the antibiotic sulfamethoxazole, the anti-inflammatories ibuprofen
and diclofenac, and caffeine, as well as pesticide degradates. This means there will
be challenges in the future in order to address these ECs and to minimise their impact
on drinking water and ecosystems. In the coming decades, more ECs are likely to
have environmental standards defined, and therefore a better understanding of
environmental behaviour remains a priority.
Keywords
Emerging contaminants; groundwater; pharmaceuticals; pesticide degradates;
personal care products
1
Introduction
A diverse array of synthetic organic compounds is used worldwide in large quantities
for the production and preservation of food, for industrial manufacturing processes
and for human and animal healthcare. In the last few decades there has been a
growing interest in the occurrence of these contaminants in the terrestrial and aquatic
environment, their environmental fate and their potential toxicity even at low
concentrations [1-6]. The contamination of groundwater resources is a growing
concern and relatively poorly understood compared to other freshwater resources [7].
1
Organic compounds previously not considered or known to be significant in
groundwater in terms of distribution and/or concentration, which are now being more
widely detected and which have the potential to cause known or suspected adverse
ecological or human health effects are here referred to as emerging contaminants
(ECs). Synthesis of new chemicals or changes in use and disposal of existing
chemicals can create new ECs. ECs also include substances that have long been
present in the environment but whose presence and significance are only now being
elucidated [8]. As analytical techniques improve, previously undetected organic
micro-contaminants are being observed in the aqueous environment [9-10].
Richardson and Ternes (2011) review recent analytical developments in the emerging
contaminant context [11].
ECs include a wide array of different compounds (as well as their metabolites and
transformation products, collectively referred to here as degradates) including;
pharmaceuticals and personal care products (PCPs), pesticides, veterinary products,
industrial compounds/by-products, food additives as well as engineered nanomaterials. Because of the vast number of possible compounds, many studies have
selected ECs according to priority lists established taking into account consumption,
predicted environmental concentrations as well as ecotoxicological, pharmacological
and physicochemical data [12-17].
To date, the occurrence of ECs has been much better characterised in wastewater
and surface water environments than in groundwater [7]. Wastewaters are the main
sources of ECs in the environment and surface waters therefore contain the greatest
loads of ECs. Wastewaters and surface waters are also thought to contain a much
greater diversity of compounds compared to groundwater, although this may be
simply a function of the capability of analytical methods relative to the generally
lower groundwater concentrations and the limited number of groundwater studies.
The occurrence of ECs in surface waters has been reviewed for public water
supply [18], for sources to public supplies, [7], and for occurrence and fate of ECs
and established trace pollutants [19]. The first systematic review of ECs in
groundwater, by Lapworth et al. (2012), highlighted the worldwide widespread
contamination of groundwater resources by a large variety compounds that are
detected as a result of both recent and historical activities [20]. Environmentally
significant concentrations (102–104 ng/L) of a range of ECs, including a number of
endocrine disrupting substances, are being detected in groundwaters globally. Many
of these ECs are among the highest priority substances for treatment and regulation
both in terms of their potential environmental and human health effects.
Many ECs remain unregulated and present analytical and institutional challenges
[21]. The number of regulated contaminants will continue to grow slowly over the
2
coming decades. Monitoring of anthropogenic micro-organic pollutants in river
basins is required within the framework of various national regulations [22-23] with
the overall aim of protecting and improving the quality of water resources.
In the European context groundwater quality is currently regulated under the
Water Framework Directive (WFD) [24], its daughter Groundwater Directive (GD)
[22] and drinking water under the Drinking Water Directive [25]. Pesticides are also
regulated under the Plant Protection and Biocides Directives [26-27]. The WFD and
the GD establish environmental objectives for protecting groundwater and water
bodies and groundwater dependant ecosystems. These require that threshold values
(standards) be established for pollutants that put the groundwater body at risk of
failing to achieve its environmental objectives. Whilst for many chemical pollutants
there is sufficient knowledge to establish threshold values, in the case of most ECs
the current lack of knowledge on toxicity, impact, behaviour and limited monitoring
data mean that threshold values cannot yet be set.
The European Drinking Water Directive sets limits for a small number of organic
micropollutants comprising aromatic hydrocarbons, chlorinated solvents and
disinfection by-products [25]. Priority substances established under another WFD
daughter directive include benzene, octyl and nonyl phenols, specified polyaromatic
hydrocarbons (PAH), di(2-ethylhexyl)phthalate and a range of chlorinated
hydrocarbons[28]. The European Commission aims to table draft limits for 16 new
substances limits under the WFD including anti-inflammatory drugs, synthetic
contraceptives and perfluorooctane sulfonate (PFOS) [29].
A similar situation occurs elsewhere in the world. Regulatory frameworks exist to
manage the potential sources of pollution and require monitoring of a number of
‘priority’ organic contaminants in the aquatic environment. However, there are a
huge number of contaminants (largely organic compounds) that are not subject to the
same degree of regulation at present (for the same reasons outlined above). The US
Environment Protection Agency (EPA) have derived statutory guideline values for
about 125 contaminants in drinking water of which 31 could be considered to be
micro-organic pollutants excluding pesticides. None of these are pharmaceuticals or
PCPs [30]. The US EPA published a new contaminant candidate list (CCL-3) in 2009
which included 3 pharmaceuticals as well as perfluorooctanoic acid (PFOA), PFOS
and eight hormones [10].
2
Types of Emerging Groundwater Contaminants
Much more is known about pesticides in groundwater compared to other compounds,
such as pharmaceuticals, which are more poorly characterised. The hazards to
human health of some compounds are well documented, but their ability to travel
3
through the aqueous environment is only just being investigated, and environmental
persistence is as yet unknown. From their sources, physical and chemical
characteristics, mobility/behaviour in the aqueous environment and associated
hazards the following types of micro-contaminants may be considered to be
emerging in groundwater.
2.1
Pesticides
Pesticides have been detected at trace concentrations in groundwater worldwide for a
considerable period and are well-established contaminants. By the 1990s atrazine,
simazine and a range of other herbicides had been found in groundwater worldwide
[31-36]. Recently new detections of parent compounds have become apparent as
analytical methods have improved, for example metaldehyde in the UK [37], and this
also fits the emerging contaminant definition.
Even twenty years ago it was clear that pesticide degradates needed to be
considered [38-39]. Some studies have even shown that pesticide metabolites may be
detected in groundwater at higher concentrations compared to parent compounds
from both agricultural and amenity use [40-41]. By their nature degradates are
biologically active and many may be toxic, and such data forms part of the pesticide
registration process although they are still often not adequately monitored.
2.2
Pharmaceuticals
The presence of pharmaceutical chemicals in the aquatic environment has long been
recognised as a concern [42]. The primary routes for pharmaceuticals into the
environment are through human excretion, disposal of unused products and through
agricultural usage [43]. A wide range of pharmaceutical products have been detected
in surface and groundwater, associated with wastewater disposal [44-48]. These have
included:
• veterinary and human antibiotics: ciprofloxacin, clofibric acid, lincomycin,
sulfamethoxazole, tetracycline
• other prescription drugs: carbamazepine, codeine, diclofenac, salbutamol,
• non prescription drugs: acetaminophen (paracetamol), ibuprofen, salicylic acid
• iodinated X-ray contrast media: iopromide, iopamidol
Other potential threats to surface water which have been identified are tamiflu
and chemotherapy drugs, such as 5-fluorourcil, ifosfamide or cyclophosphamide [4952] and illicit drugs such as cocaine and amphetamines [53-54].
4
2.3
“Life-style” Compounds
Caffeine, nicotine and the nicotine metabolite cotinine have been widely detected in
groundwater impacted by sewage effluent [55-57]. The artificial sweeteners
acesulfame, saccharine, cyclamate and sucralose have been found at high
concentrations in groundwater impacted by sewage infiltration ponds [58]. Buerge et
al. (2009) showed acesulfame to be widely detected in the aquatic environment due
to its use, mobility and persistence [59].
2.4
Personal Care Compounds
PCPs contain a wide range of compounds are commonly transmitted to the aqueous
environment through sewage treatment works. These have included:
• N,N-diethyl-meta-toluamide (DEET), the most common active ingredient in
insect repellents
• parabens – alkyl esters of p-hydroxybenzoic acid, used since the 1930s as
bacteriostatic and fungistatic agents in drugs, cosmetics, and foods
• bacteriocide and antifungal agents – triclosan is widely used in household
products, such as toothpaste, soap and anti-microbial sprays
• polycyclic musks – tonalide and galoxalide are used as fragrances in a wide range
of washing and cleaning agents and PCPs
• UV filters/sunscreen – organic filters include the benzophenones and
methoxycinnamates
Lindström et al. (2002) detected triclosan and its metabolite methyl triclosan in
surface water in Switzerland, and considered the metabolite to be persistent [60].
Tonalide (AHTN), galoxalide (HHCB) and HHCB-lactone have been detected in
wastewater [61] and these compounds have been used as markers for wastewater in
surface waters [62-63]. Heberer (2002) discussed the results from investigations of
synthetic musk compounds found in sewage, sewage sludge, surface water, aquatic
sediment, and biota samples in terms of bioaccumulation, metabolism in fish, and
environmental and human risk assessment [64]. The majority of compounds used as
sun screens are lipophilic, conjugated aromatic compounds, but are still detected in
the aqueous environment [65].
2.5
Industrial Additives and By-products
There are a wide range of industrial compounds which can be released to the
environment and many of these have led to well-established problems. Examples
include chlorinated solvents, petroleum hydrocarbons, including polyaromatic
hydrocarbons and the fuel oxygenate methyl tertiary-butyl ether, and
plasticisers/resins bisphenols, adipates and phthalates [65-69]. Most of these
5
industrial compounds are classed as priority pollutants or now have drinking water
limits and as such are not emerging contaminants. However, some breakdown
products may be regarded as emerging contaminants. Industrial ECs may include:
• 1,4-dioxane, a 1,1,1,-trichloroethane stabiliser which is soluble in water, resistant
to biodegradation, does not readily bind to soils, and readily leaches [70]
• Benzotriazole derivatives which are found in antifungal, antibacterial, and
antihelmintic drugs and are persistent in the aqueous environment [71-72]
• Dioxins produced as a consequence of degradation of other micropollutants e.g.
from the antimicrobial additive triclosan [73-74]
2.6
Food Additives
Some food additives are considered to be oxidants or endocrine disruptors [75].
Triethyl citrate is used as a food additive to stabilise foams as well as for
pharmaceutical coatings, and is also a plasticiser. Butylated hydroxyanisole and
hydroxytoluene are used to preserve fat in foods. Other food additives include
camphor, 1,8-cineole (eucalyptol), citral, citronellal, cis-3-hexenol, heliotropin,
phenylethyl alcohol, triacetin, and terpineol.
2.7
Water Treatment By-products
The trihalomethanes and haloacetic acids are well established by-products of water
disinfection [76]. More recent concern has focused on N-nitrosodimethylamine
(NDMA) as a drinking water contaminant resulting from reactions occurring during
chlorination or from direct industrial contamination. Because of the relatively high
concentrations of this potent carcinogen formed during wastewater chlorination, the
intentional and unintentional reuse of municipal wastewater is a particularly
important area [77]. The change from disinfection with chlorine to ozone and
chloramines can increase levels of other potentially toxic by-products [42]. Other by
products of water treatment can include polyacrylamide and epichlorhydrin [74].
2.8
Flame/Fire Retardants
Polybrominated diphenyl ether flame retardants are extensively used in resins for
household and industrial use [78], and may enter the environment via waste disposal
to landfill and incineration. Phosphate-based retardants such tris-(2-chloroethyl)
phosphate appear to work by forming a non-flammable barrier are used in industrial
and consumer products [79].
2.9
Surfactants
A range of anionic, cationic, amphoteric and non-ionic surfactants and antifoaming
agents are commonly found in wastewater [80]. The priority pollutants octyl- and
6
nonyl-phenol (OP and NP) are used in the production of alkyl phenol ethoxylates
(APEs) for the manufacture of non-ionic surfactants. Both the parent ethoxylates and
their metabolites, alkyl phenols and carboxylic degradation products, have been
shown to persist in the aquatic environment [81-82]. Non-ionic polyethylene glycolbased compounds are used as anti-foaming agents. Siloxanes are used in many PCPs
as anti foaming agents and there is concern about their potential toxicity and
transport in the aquatic environment [83].
Cationic surfactants include quaternary ammonium salts, such as cetrimonium
chloride, are used as emulsifiers, antiseptics and homologues have been identified as
emerging contaminants in marine sediments [84]. Amphoteric surfactants include
coconut-based products such as the widely used cocamidopropyl betaine. Anionic
surfactants, including perfluorinated compounds such as PFOS and PFOA, have been
used for over 50 years in food packaging and cookware coatings, paints and
surfactants, cosmetics and fire-fighting foams. They are found in wastewater and
surface water and are very persistent in the environment [85-86]. PFOS was found in
sewage effluent in Japan and has also been detected in surface water [87-88].
2.10
Hormones and Sterols
Sex hormones include androgens, such as androstenedione and testosterone, and
estrogens such as estrone, estriol, 17α- and 17β-estrodiol, and progesterone. There
are also synthetic androgens such as nandrolone and more importantly synthetic
estrogens (xenoestrogens) such as 17α-ethinylestrodiol and diethylstilbestrol, widely
used as contraceptives. Some of these compounds are commonly present in
wastewater and treated effluent [47, 89-90]. A related group of compounds are
cholesterol and its metabolite 5β-coprostanol, and the plant sterols stigmastanol,
stigmasterol and β-sitosterol. Plant sterols (phytoestrogens) are ingested from plants
and excreted to wastewater, which may be the largest source of these compounds in
the environment [91].
2.11
Ionic Liquids
Ionic liquids are salts with a low melting point which are being considered as ‘green’
replacements for industrial volatile compounds [10, 92]. These compounds have
nitrocyclic rings (e.g. pyridinium, pyrrolidinium or morpholinium moieties) or are
quaternary ammonium salts. Ionic liquids are not yet widely used but current
formulations have significant water solubility and are likely to be toxic and poorly
degradable [92].
7
3
Sources to the Environment
3.1
Concepts
The transport of contaminants in the aqueous environment can be described by a
source-pathway-receptor model, which considers the source of the contaminant, the
pathway by which it travels from the source and the receptor. Fig. 1 shows this
approach for groundwater pollution by ECs. For many ECs the pathway from the
source to the receptor is unclear, since there is a paucity of information for such
contaminants. Direct pathways for urban and industrial contaminants, and
pharmaceuticals, to reach groundwater include leaking sewers, discharge of effluent
(directly to ground or to surface water which then infiltrates), landfill leachate,
leaking storage tanks and discharges to the ground bypassing the soil zone, such as
septic tanks (Fig. 1). Pathways to humans and groundwater from human and animal
pharmaceuticals have been proposed [3, 94-95]. Compounds which pose a threat
include those which remain difficult to analyse for at low concentrations and those
which have physicochemical properties which allow them to persistent during and
after drinking water treatment.
3.2
Diffuse Source Terms
Diffuse (non-point-source) pollution originates from poorly-defined sources that
typically occur over broad geographical scales. For example, the majority of
pesticide applications have been for agriculture and horticulture. Once released
pesticides may be degraded by both biotic and abiotic processes. Stuart et al. (2012)
discuss risk assessment approaches for pesticide degradates [96].
Landfill
Animal
waste
Pesticide and
herbicide use
Domestic
waste/eff.
Hospital
waste/eff.
Industrial
waste/eff.
Old unlined sites*
MAR
Septic
tanks
Lagoon leakage*
Sources and pathways
bypass fracture flow*
Major source
Minor source
Majo …
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