Environmental Engineering Reference
In-Depth Information
decomposition; inhibition or stimulation of growth in aquatic plant and algae
species; and the development of antibacterial resistance in soil microbes.
Whilst many of these effects have been seen at environmentally realistic
concentrations, the significance in terms of environmental health has yet to
be established; this will be one of the challenges in the coming years.
Transformation products
During their use and subsequent release to the environment, synthetic chemi-
cals (pesticides, pharmaceuticals, biocides and industrials) may be degraded by
a variety of processes (e.g., Roberts 1998 ; Roberts & Hutson 1999 ). Consequently,
the environment may be exposed to a mixture of the synthetic chemical itself
('parent' compound) and any resulting degradation products ('degradates').
Recent advances in analytical methodology and greater access to analytical
standards have allowed for increased research on the environmental occur-
rence of degradates. Research on pesticides has shown that degradates can be
found in surface water, groundwater, precipitation, air and sediment (Boxall
et al. 2004b ). Although most studies have been on pesticides, degradates from
other chemical classes (e.g., pharmaceuticals and detergents) have also been
found in the environment. In some cases, degradates were detected as often or
more frequently than the parent compound (Boxall et al. 2004b ).
Even though some regulatory schemes require that the impacts of degra-
dates on human and environmental health are considered, for many com-
pounds this information is limited or non-existent. The main exception is for
pesticides where not only the risk of the parent compound itself is assessed but
also the impacts of major degradates.
Environmental fate of degradates
Once released to or formed in the environment, degradates may be transported
and distributed between the major environmental compartments. The concen-
trations in these compartments depend on a number of factors and processes,
including (1) the release scenario of the parent compound, (2) the rate of
formation of degradates, (3) the half-lives of the degradates and (4) their
distribution behaviour, e.g., their partitioning to sludge, soil and sediment
and movement to air and water.
The mechanism, route and rate of degradation of a substance will vary across
compartments, for example, if a pesticide is applied to soil, degradation by soil
microbes may be important, whereas if the same substance is released directly
to a water body, hydrolysis may be a more important mechanism. Climatic
conditions (e.g., soil moisture content and sunlight) and the characteristics of
the receiving environment (e.g., pH) may also have an impact. For example,
photodegradation may be a more important degradation route in tropical
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