In April, the Institute of Hydrology found
from work at a Ministry of Agriculture Fisheries and Food (MAFF) farm site that
cracked soils mean that pesticides can reach ground water quicker and in much
larger quantities than had been predicted(1). In May, the NRA acknowledged a new
herbicide, bentaxone, was being found in water-in excess of EU limits-that
had not been looked for previously(2). In October, a review of pesticide
pollution levels in surface water in northern Europe concluded that water
standards that were designed to protect human health were often not sufficient
to protect aquatic wildlife(3).
The National Rivers Authority (NRA) used the occasion of the
BCPC Conference at Brighton to announce its report on the presence of pesticides
in water(4) and its concern that "... the significance of long term exposure
to pesticides and their combined effects on the environment are not fully
understood ... further action needs to be taken now to minimise the risks of
pesticide pollution and avoid potential problems for the future."
NRA recommendations
Although it emphasises that the overall levels of
pesticides in surface and ground water are low and that these levels are, on the
whole, unlikely to cause immediate damage to the water environment, NRA
acknowledges that the effects of cumulative long term exposure are difficult to
predict. NRA recommends a number of actions in support of 'pesticide
minimisation' including:
a minimum no-spray buffer zone of 6 metres adjacent to water courses;
assessment of the economics of Water Protection Zones, where the costs of water treatment would be compared with the costs of controlling pesticide inputs;
a licensing scheme for sheep dip sites and a detoxification treatment for spent dip;
better control of effluent from textile companies that use pesticides in processing.
Cases for concern
NRA has outlined a number of case studies of its
concerns:
Bentazone
The herbicide bentazone is being detected with
increasing frequency, in spite of a relatively low usage (up to 60 tonnes pa).
NRA may recommend restrictions on usage if elevated concentrations continue to
be found.
Diazinon
Diazinon is an OP insecticide used in sheep dipping
and is found in the effluent from textile factories after scouring of the dipped
fleeces. Diazinon also reaches water by careless soakaway disposals or other
methods. Environmental Quality Standards (EQSs) have been exceeded in the Rivers
Severn, Aire, Calder and Dart. NRA may seek reduction of the use of diazinon in
dipping, but is also concerned that alternative dipping products like
pyrethroids "can be up to 100 times more toxic to aquatic life".
Atrazine, simazine and diuron
Although non-crop restrictions on the use of both
atrazine and simazine have been in force for some years, levels of both products
are falling in surface waters, but not yet in groundwaters. Atrazine also has a
relatively new UK use as a herbicide on maize. If levels in water increase,
Water Protection Zones will be considered. Diuron, the new choice as a
substitute residual herbicide, will be monitored as levels are increasing.
Isoproturon
In March 1994, Southern Water Services closed its
water intake on the River Eastern Yar, Isle of Wight, because of contamination
by the herbicides isoproturon and chlorotoluron. It is thought the concentration
arose through legitimate use, rather than careless or illegal use of the
products. MAFF has recently advised a reduction of 40% in the application rate
of isoproturon in an effort to reduce contamination in water and to prevent the
product being restricted even more.
The Rosemaund Farm trials
Measurements of pesticides in water at MAFF's
Rosemaund Farm site (operated by ADAS) showed that, particularly after rainfall,
"the use of pesticides even when applied according to normal agricultural
practice will probably lead to the contamination of surface waters in the
catchments into which they drain." Rainfall can flush pesticides through
cracks in the soil structure much faster than leaching or sorption theories
predict. The trials raise a number of points:
similar conditions of highly structured soil with underdrainage forms 45% of the agricultural land of the UK;
rain can cause flushes of water with high if short-lived concentrations of pesticide;
run-off of carbofuran was such that the resulting concentration in catchments would be fatal to the freshwater shrimp;
even pesticides that are highly sorbed onto soil particles are washed with soil into catchments and may present a threat to aquatic fauna;
out of 93 samplings, 80 were in excess of the EU Maximum Admissible Concentration of 0.1 µg/l.
MAFF considers that the passage of pesticides to water is almost inevitable, and that improved management application may be the answer, rather than new molecules. (PB)
References
1. Total Impact Assessment of Pollution in River Basins: Pesticide Impact Modelling. Institute of Hydrology R&D Note 404. Foundation for Water Research, Marlow, Bucks, 1995
2. NRA Discovers 'New' Pesticide Polluting Groundwaters. ENDS Report 244, May 1995.
3. Pesticides in Surface Waters. HMSO, London, 1995, £4.50
4. Pesticides in the Aquatic Environment. Report of the National Rivers Authority. Prepared by the National Centre for Toxic and Persistent Substances (TAPS). Water Quality Series No. 26. HMSO, London, 1995, £25. 92pp.
[This
article first appeared in Pesticides News No. 30,
December 1995, page 15]