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174 Soil and Water Contamination
2012). The term ‘substances’ rather than ‘contaminants’ is used to recognise the fact that
some of these substances are of natural origin.
Considerable uncertainty surrounds the environmental transport, fate and toxicological
effects of ESOCs, since they are not often routinely measured in environmental monitoring
programmes, or their precise toxic effects are still unknown. The lack or absence of
environmentally relevant information of substances is not surprising, given the vast number
of new organic compounds. By 2013, the CAS Registry database, the most comprehensive
substance database maintained by the Chemical Abstract Service (a division of the American
Chemical Society), contained descriptions of more than 71 million organic and inorganic
substances and approximately 12 000 new substances were being added every day.
Categories of ESOCs include current-use pesticides, pharmaceuticals and personal care
products (PPCPs), and endocrine-modulating compounds (EMCs). As is the case with the
classification of organic pollutants in general, the various classes of ESOCs also overlap: for
example, some pesticides and pharmaceuticals have endocrine-modulating properties, and
personal care products may contain nanoparticles. In addition to the above classes of ESOCs,
microplastics, i.e. particles of plastic debris smaller than 1 or 5 mm, have been identified as
an emerging global environmental issue, especially in the marine environment. The various
categories of ESOCs are discussed below.
9.7.1 Current-use pesticides
Current-use pesticides include modern agricultural and domestic pesticides, such as
glyphosate, atrazine, and alachlor. Although widely used, they are less persistent than past
pesticides such as DDT, dieldrin and aldrin.
Glyphosate, also known by its trade name Roundup, is a herbicide used to kill
broadleaved weeds and grasses in agricultural and urban areas. It is the mostly widely used
herbicide in the world. Glyphosate is considered to be relatively low in acute toxicity: in
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rats, the oral LD50 of pure glyphosate is 4230 mg kg . It is not carcinogenic and barely
bioaccumulates. Despite being chemically stable in water and not subject to photochemical
degradation, glyphosate degrades microbially in soil, aquatic sediments and water. It also
binds readily to particles. The sorption mechanisms of glyphosate to soils and sediments
are not yet fully understood, but in general, sorption is controlled by available phosphate
binding sites, which means that sorption is promoted in the presence of combinations of
clay, sesquioxides and organic matter. Given its low mobility in soil, there is minimal
potential for glyphosate contamination of groundwater. Glyphosate can, however, enter
surface and subsurface waters through direct aquatic applications or through runoff or
leaching from terrestrial applications. In a recent study in the Mississippi basin (Coupe et al.,
2011), glyphosate was frequently and consistently detected in surface waters, rain and air,
which indicates it is transported from its point of use into the broader environment.
Another well-known agricultural herbicide is atrazine. Although it has been banned
in European Union since 2004, it is still one of the most widely used herbicides in the
world. As is the case of glyphosate, the World Health Organisation classifies atrazine as a
pesticide unlikely to present acute hazard in normal use. The acute oral LD50 for rats is
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1869-3090 mg kg , indicating its relatively low toxicity, although ruminants seem to be
much more sensitive to the acute toxic action than rodents. The carcinogenicity of atrazine
is rather controversial, but the United States Environmental Protection Agency classifies
it as being unlikely to be carcinogenic to humans. Atrazine is an endocrine-modulating
compound and may cause low oestrogen levels and menstrual irregularities in women, even
when it occurs in drinking water at concentrations far below the drinking water threshold
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of 3 μg l . For aquatic organisms, serious effects have been observed on frogs’ sexual
development: at levels often found in the environment, atrazine causes demasculinisation of
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