Sales of pyrethroid dips have been increasing because of concern among farmers about the health hazards of exposure to organophosphates. In 1995, the switch was accelerated by a statutory requirement on farmers to be certified to buy organophosphates.
However, while pyrethroids are less hazardous to humans, some are extremely toxic to aquatic life - especially cypermethrin, which is supplied by Grampian. The proposed freshwater quality standard for the chemical is 0.001µg/l as a maximum concentration - 100 times tighter than that for diazinon, an organophosphate commonly used in sheep dips.
Cypermethrin is known or suspected to have caused several serious pollution incidents in Cumbria and Scotland in 1995 and 1996. Invertebrate life along 100 kilometres of river suffered severe damage (ENDS Report 263, pp 4-5 ).
Another three incidents have occurred within the past few weeks. At the end of April, the Environment Agency reported "severe depletion" of invertebrate life along an eight-kilometre stretch of the Afon Twrch and a tributary in north Wales. A pyrethroid dip is believed to be responsible, and prosecution of a farmer is likely.
The other two incidents were reported to the ACA. In one case, a discharge of spent sheep dip into a tributary of the river Wye in Wales caused a significant kill of invertebrates and small fish.
In the second incident, an angling club which leases fishing rights on the river Ellen in Cumbria discovered that the whole river was devoid of insect life. The few brown trout present were emaciated and likely to starve to death. The club is confident that sheep dip is the cause.
In a letter to Grampian and Bayer in May, the ACA's solicitor, Simon Jackson, contended that they are liable to those who have suffered loss and damage to their fishing rights.
The letter points out that the Consumer Protection Act 1987, which implemented the EC Directive on liability for defective products, imposes strict liability where damage is caused wholly or partly by a defect in a product. A defect exists where a product's safety is not what people are entitled to expect, and a product can either be inherently defective or become so as a result of improper use. Any person suffering loss as a result of such a defect can sue for damages.
The "catalogue" of pollution incidents caused by pyrethroid dips leaves "no doubt" that they are defective within the meaning of the 1987 Act, according to Mr Jackson - they are a "disaster waiting to happen."
The ACA would break new ground if it brought a claim under the 1987 Act, which is believed not to have been used at all since it came into force - and certainly not to obtain redress for pollution. The two companies will doubtless be aware that the ACA has a good record of success in civil claims for damage to fishing rights.
However, the ACA has offered them an alternative. It wants them to pay for a working group which would evaluate the risks posed by their products, develop treatment and disposal methods for spent sheep dip, and develop improved analytical techniques for detecting pyrethroids in water. The group would include representatives of the environment agencies, river users and Government Departments as well as the two firms and the ACA.
The ACA is also demanding the establishment of a trust fund to pay for the reinstatement of rivers affected by sheep dip and provide compensation for damage to fishing rights.