Geology Reference
In-Depth Information
has resulted in the death of aquatic organisms in UK rivers. Pyrethroids,
which do not persist in the environment and are largely non-toxic to
mammals, are toxic to invertebrates and are estimated to be at least 100
times more toxic in the aquatic environment than organophosphorus
pesticides. It appears to be the pouring of waste dip into holes in the
ground that has caused the problem.
162
In order to protect the aquatic
environment, the Environment Agency in England assesses water qual-
ity against EQSs. Defined as the concentration of a substance which
must not be exceeded within the aquatic environment in order to protect
it for its recognized uses, EQSs are specific to individual substances,
including pesticides.
Atrazine, now banned in many European countries but which still
accounts for 40% of all herbicide applied in the USA and is most often
applied in the spring, is routinely present in streams, rivers, and
reservoirs at levels of 1-10 mgL
1
, close to the USEPA standard of 3
mgL
1
.
163,164
Runoff peaks of 100-200 mgL
1
, however, have been
recorded at the times when frogs are breeding and tadpoles are devel-
oping. Atrazine is therefore suspected of causing the gonadal abnorm-
alities, such as retarded development and hermaphroditism, found in
male wild leopard frogs in different regions of the USA.
163
(cf. Section
3.3.5.2.3)
3.3.5.2.2 Polychlorinated biphenyls (PCBs). The Great Lakes, the
largest body of freshwater in the world, with long hydraulic residence
times, long food chains, and multiple sources of PCBs, have been the focal
point of PCB research in aquatic systems. The distribution of PCBs
between the dissolved and particulate phases is dependent on the con-
centration of suspended particulate matter, dissolved and particulate
organic carbon concentrations, and the extent to which the system is at
equilibrium. In the 1990s, water concentrations of up to 0.6 ng L
1
were
observed in the most contaminated lakes (Michigan, Erie, and Ontario),
which may be compared with the USEPA Great Lakes Water Quality
Guidance criteria of 0.017 ng L
1
. Sediment concentrations peaked in the
1970s, the period of maximum PCB production in the USA. Following a
ban upon their North American production during the 1970s, there was a
significant decline in the PCB concentrations of Great Lakes' fish from
the mid-1970s to the mid-1980s but the rate of decrease has since slowed
or stopped for all lakes.
165
In common with other organochlorine
compounds, it is the stability, persistence, volatility, and lipophilicity of
PCBs, which lead to considerable biomagnification along the food chain,
often far from the place of release. To these traditional halogenated
contaminants can now be added fire-retardant polybrominated diphenyl
