Agricultural Chemicals and the Environment produced by the Royal Society of Chemistry provides a wide-ranging discussion on the impact of fertiliser and pesticide use in the UK. In this report, scientists at the National Rivers Authority (now the Environment Agency [EA]) have produced an overview of the environmental impacts of pesticides in water. It is a very competent assessment of the current concerns which arise from the presence of pesticide residues in the water environment.
North Sea contamination
Since the 1980s, pollution in the North Sea has been
addressed by a series of ministerial conferences attended by countries bordering
the North Sea. The UK, along with other governments, has agreed to reduce
emissions of 36 Red List hazardous substances of which 18 are pesticides. It has
proved much easier to reduce compounds arising from point source discharges,
such as effluent discharges. Pesticides have been more difficult to control
because they enter the North Sea from diffuse inputs, such as the normal use of
pesticides.
Levels of the Red List herbicide trifluralin did in fact
increase in 1993 and again in 1994. This is difficult to explain because
Ministry of Agriculture Fisheries and Food (MAFF) usage figures indicate that
trifluralin usage declined over the same period.
The loads for the insecticide lindane (gamma-HCH) have
declined since 1990, but are now starting to level out. The levels indicate that
diffuse pesticide inputs as a result of use in agriculture and domestic
situations (such as treatment for headlice), are much more difficult to control.
The authors suggest that the UK government will need to consider new actions to
reduce the loads of pesticides arising from diffuse sources if the agreed
reduction targets are to be met.
Herbicide residues from agricultural use
The herbicides atrazine, simazine, isoproturon and
mecoprop are the most frequently detected pesticides in drinking water at levels
above the 0.1 µg/l limit set by the EU. The Anglian region, an intensively
farmed area, is where most residues are detected.
Problems with atrazine and simazine principally arose as a
result of their use in amenity situations. Since their ban for
non-agricultural purposes, concentrations have generally declined. However both
these pesticides still have some agricultural uses (atrazine on maize and
simazine on a wide range of crops), so the risk of pollution still exists when
these pesticides are applied in drinking water supply catchment areas from
either groundwater or surface water sources. Problems have already been
encountered in the South West of England where the area under maize is
increasing.
Isoproturon (IPU), a heavily used herbicide applied to
control blackgrass, has contaminated surface and groundwater. This has been a
particular problem where water is abstracted for drinking water. The problem of
IPU contamination was highlighted on the Isle of Wight in March 1994. The public
water supply intake on the River Eastern Yar had to be closed due to the
unacceptable levels of IPU and chlortoluron. The NRA investigation found that
pollution arose as a result of 'normal' agricultural spraying.
The particularly wet autumn and winter meant most farmers
concentrated their IPU applications into a three week period. Heavy rainfall
after these applications led to large flushes of IPU entering surface water
sources. As a result of general contamination the Advisory Committee on
Pesticides recommended to MAFF that IPU use continue subject to certain
restrictions. Part of the subsequent MAFF restrictions imposed a maximum dose
rate of 2.5kg/ha. The NRA was not happy with this, maintaining that 1.5kg/ha
would be more appropriate and the most effective way of reducing IPU
concentrations in surface waters.
Environmental quality
The NRA (now the EA) is in the process of developing
Environmental Quality Standards (EQSs)-the concentration of a substance which
must not be exceeded within the aquatic environment in order to protect it for
its recognised uses. According to the NRA, results indicate that, in a small
number of sites, the EQS for gamma-HCH has been exceeded. Most are associated
with polluted sites, but diffuse inputs are thought to be responsible for
others. At present, gamma-HCH is the only agricultural pesticide with an EQS.
There are 11 others with proposed values-atrazine and simazine combined,
malathion, trifluralin, diazinon, IPU, chlorotoluron, mecoprop, MCPA, cyfluthrin
and permethrin.
NRA/EA conclusions
The full extent of the toxicity of pesticides is not
known. Although chronic toxicity testing is required for new substances, little
is known about the long-term effects of older pesticides. Also, very little is
known about the toxicity and occurrence of the products formed when pesticides
break down or the many 'non-pesticidal' additives used in pesticide
formulations. However, the future is looking brighter, says the NRA/EA. New
modelling techniques, EQS development, and the use of newer, less persistent
pesticides with lower dose rates, should help reduce pesticide pollution.
Agricultural Chemicals and the Environment, Issues in Environmental Science and Technology, Eds. R.E. Hester and R.M. Harrison, Royal Society of Chemistry, Turpin Distribution Services, Blackhorse House, Letchworth, Herts, SG6 1HN, Tel, +44 (0)1462 672555, Fax +44 (0)1462 480947, £17.50 (US$32.00), 128pp.
[This
article first appeared in Pesticides News No. 33, September 1996,
page 26]