Pesticides in Ground Water

Three recent reports from the United States show that pesticides are routinely and continually being found in ground water which is used to supply drinking water. The same pesticides are in use in the UK and elsewhere in Europe but their presence in water is not necessarily monitored.

A US Environmental Protection Agency (EPA) report on pesticides in ground water(1) published in September 1992 but only now released for public use summarises the data collected by monitoring programmes throughout the US between the years 1971-1991. This is not the report of a single nation-wide monitoring programme, but a compilation of several studies.

    On a general level this report shows which pesticides can enter ground water and which regions are vulnerable to contamination by pesticides. This data can be correlated with, for example, crop data or geological data to develop a picture of regional sensitivity which can also be used to develop early warning systems.

265 pesticides detected in ground water   

In total 68,824 ground water wells in 45 States were sampled and pesticides were detected in 16,606 wells in 42 States. This is as much an indicator of the quality of monitoring as a warning of pesticide contamination. Clearly in States where more wells were sampled, there was a greater likelihood that pesticides would be detected. Similarly, pesticides were more likely to be found in ground water situated in agricultural areas.

    Analysis was carried out for a total of 605 pesticides and related compounds, of which 265 were detected at least once. Of the pesticides detected, 28 are no longer in use in the US, and regulatory restrictions have been placed on 54.

    From a non-US perspective, the nature of this compilation provides little more than an indication of which pesticides have the potential to enter ground water, but this in itself is of some interest.

Bromacil and oxamyl implicated

Two further American studies published by the consultancy Disposal Safety Incorporated in July report that the herbicide bromacil and the insecticide oxamyl are routinely found in ground water at concentrations far higher than the current 0.1 µg/l limits set by the EC Drinking Water Directive(2,3).

    Bromacil is a soil acting herbicide used in non-crop areas and in cane fruit plantations in the UK. It is also sold in formulations with other herbicides such as diuron, picloram and amitrole for total weed control in non-crop areas. Oxamyl is a systemic soil applied nematicide and insecticide approved for use in various root and vegetable crops in the UK. The use of both products is less extensive in the UK than it is in the US, but their application in vulnerable areas may lead to ground water contamination. Despite their known potential for leaching into ground water, neither bromacil nor oxamyl are routinely tested for by water companies in the UK(4). One company which did test for bromacil Wrexham and East Denbighshire found it at levels above the legal limit.

    Campaigners in the US and the UK have called for a moratorium on the use of bromacil and oxamyl to reduce the risk of ground water contamination. It is virtually impossible to decontaminate polluted aquifers where ground water collects, and increasingly in the US wells which previously yielded drinking water are being abandoned as they are found to be contaminated.  The British water industry is being forced to invest billions of pounds in monitoring and cleanup technology while not enough is being done to prevent water contamination at source. (MD)

1. US-EPA, Pesticides in ground water database. A compilation of monitoring studies: 1971-1991 National summary, Washington, US, 1992.

2. Disposal Safety Incorporated, Oxamyl and European water quality standards, Washington, US, 1993.

3. Disposal Safety Incorporated, Bromacil and European water quality standards, Washington, US, 1993.

4. Pers. comm, Drinking Water Inspectorate, London, 19 August 1993.

[This article first appeared in Pesticides News No.21,September 1993, page 18]