Environmental Engineering Reference
In-Depth Information
layers. Another portion of the pesticide sprays may become drifted or in the case
of substantial precipitation get washed into surface waters, or slowly move toward
groundwater. Triazine herbicides used for weed control in maize, e.g., atrazine,
undergo medium rate decomposition in the upper soil layers, while the decomposi-
tion rate drastically drops when these compounds are leached into deeper layers with
lower oxygen content. In turn, further decomposition stops, the triazine concentra-
tion reaches a constant value in contaminated soil layers, and becomes a persistent
groundwater contaminating source. This is deteriorating not only for soil, but also
for drinking water quality, where groundwater (water accumulated above the first
confining layer) serves as a drinking water resource. The EU Drinking Water Directive
(DWD, 1998) has set the maximum admissible concentrations of each pesticide residue
(combined concentration of the active ingredient and its metabolites) at 0.1
µ
g/L and
µ
the total concentration of all pesticides at 0.5
g/L. Moreover, a threshold value is also
set for most toxic substances at 0.03
g/L.
Because of the ongoing chemical pressure on the environment by pesticide appli-
cations, the complex and costly process of monitoring of pesticide residues in soils and
waters is required to assure compliance with the corresponding legal requirements.
It is impossible at present to assess the presence and scope of the residues of numer-
ous pesticides likely to have adverse effects on health. The pesticides most frequently
detected in water are atrazine, simazine and bentazone (European Commission, 1999),
alachlor and acetochlor (WHO, 2008), glyphosate and its metabolites (Hamilton &
Crossley, 2004; WHO, 2005; Villeneuve
et al.,
2011; Székács & Darvas, 2012). These
all are substances of broad-spectrum herbicides used not only in agriculture, but also
in industry and households. Besides agricultural activities, a considerable proportion
of pesticide residues originates from industrial pesticide production, pesticide use by
railway companies, road maintenance/conservation services, private individuals and
local communities.
Pesticides and their residues reaching living organisms may undergo diverse
processes such as degradation or transformation during metabolization as well as
bioaccumulation. The vast majority is metabolized by the enzymes of the living organ-
isms to water-soluble derivatives able to be excreted. A smaller part of them (mostly
chlorinated hydrocarbons) is, however, subject to bioaccumulation and long-term
storage in lipid-rich tissues. This process is further acerbated by biomagnification,
when bioaccumulative compounds are transported and reach increasing concentrations
along the food chain.
The key factor in the potential occurrence of chronic environmental and human
health effects is the rate of exposure (Table 4.2). Persistency of a compound results
in extended exposure. Agrochemical agents and procedures based on persistent sub-
stances causing most severe environmental health problems have been withdrawn
from the practice, although certain organomercury seed treatment agents and chlori-
nated hydrocarbons (camphechlor, lindane) remained in use as long as until the 1990s
(Darvas & Székács 2006). Screening for biological side effects such as mutagenicity
of pesticide compounds on prokaryote as well as lower and higher order eukaryote
organisms, became a required part of the pesticide authorization process. Nonethe-
less, a significant part of the presently registered pesticides shows certain mutagenicity
according to the Genetic Activity Profile (GAP) database of the International Agency
for Research on Cancer (IARC, 2013) and the US Environmental Protection Agency
µ
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