Pesticides in water – new PAN UK briefing

Farmers and local authorities together used nearly 25,744 tonnes of pesticide active ingredient in the UK during 1999, made up of some 400 different pesticide chemicals: a proportion of this total ends up in water sources. Only now are regulators realising that the presence of pesticides in water is almost inevitable, however carefully farmers use them. Careful use can reduce the amount of pollution, but can never prevent it completely. This article is based on the new PAN UK briefing covering issues related to pesticides in water.

The cost of clean up – Water companies in England and Wales are paying £100 million a year to make sure their drinking water is treated to meet the European standard for individual pesticides.

How pesticides get to water
Pesticides may be washed into ditches and rivers by rainfall; surface waters may receive pesticide sprays either intentionally (e.g. in order to control water weeds) or unintentionally (e.g. when crops are sprayed near ditches or streams). Pesticides sprayed on hard surfaces are subject to particularly high runoff into drainage pipes and sewers. Pesticides frequently volatilise into the air. Depending on their stability they can be taken up into the atmosphere and transported long distances. They may then return to the ground through rainfall.
    Pesticides are found in many different waters. They can be transported great distances in surface and river waters. Pollution can be traced for hundreds of kilometres in rivers, either in solution or attached to particulates. From water, pollutants can be deposited in sediments where they can be taken up by bottom dwelling species. Concentrations of TBT in the sea at two parts per hundred billion can have an endocrine disrupting effect on marine molluscs. Pesticides are found in rain in parts of Europe, sometimes at levels so high that it would be illegal to supply it as drinking water. In Spain rainwater contains lindane, and 2,4-D has been found in rainwater in Italy.  Until relatively recently pesticides were regularly found in drinking water. The European Union set the limits on a precautionary basis at 0.1 µg/l (one part per billion). In 1992 3% of samples contained a pesticide in excess of this limit; in 1998 only 0.01% of samples contravened the limit, indicating how successful – at a cost – water companies have been in reducing pesticides in the water supply. The capital costs of installing equipment to remove pesticides from water have been put by the industry at one billion pounds, and the ongoing operating costs at a figure of between tens of millions of pounds up to the low hundreds of millions per year. 
    There is heightened concern of pesticides contamination of non-drinking waters. Only 65 of the 400 or more pesticides in use have Environmental Quality Standards (EQSs). 30 pesticides with EQS values that were monitored in 1997 exceeded their EQS value at least at one site. The most frequent EQS failure in surface fresh waters was permethrin (81 sites) from sheep dipping, and in marine waters tributyltin (140 sites) used as an anti-fouling paint on boats. 14% of freshwater sites monitored failed at least one EQS.

Some of the problems
Pesticides are in water not because users are wilfully careless or negligent. Generally, most of the pesticide that finds its way to water does so as a result of the legitimate use by farmers of legally approved pesticides, rather than because of misuse or abuse of pesticides. A recent study found that at least half of the herbicide found in the farm stream originated from the farm yard rather than from field losses – it happened when washing down the tractor and sprayer after use on a concrete hard standing which drained straight into the water course. 
    It is difficult to discover what pesticides are in water if methods of analysis and testing are inadequate. A review across the EU of the impact of pesticides in water found that ‘acceptable analytical methods are only available for approximately a quarter of all active substances’. It also noted that techniques for insecticides and fungicides were especially required. Most analysis tends to focus on herbicides. 
    Water sources also receive inputs of many different chemicals. There is additional concern about the impact of chemicals in mixtures, particularly where some aquatic organisms will be exposed to chemicals that can exert similar adverse impacts on the same target organisms – such as organophosphates or endocrine disrupting pesticides.

Proposed solutions
In recognition of the current impacts of pesticides on water, the Pesticides Safety Directorate introduced in 1998 the Local Environmental Risk Assessment for Pesticides (LERAPs) scheme. This means that for certain pesticides (category A pesticides) carrying a risk of run-off to water, there is a mandatory five metre buffer zone between the area of the field that can be sprayed, and the water course. For slightly less risky pesticides (category B) the buffer zone can be reduced if the user carries out and records a LERAP assessment for the pesticide in question. This may be helpful in reducing some aspects of water contamination by spray drift and run-off, but much of the risk arises from pesticides getting into water in other ways. It would be better to prevent pesticides reaching water in the first place, rather than paying water companies to try and remove them afterwards. (By Peter Beaumont)

[This article first appeared in Pesticides News No.49, September 2000, p5]