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Groundwater is an important resource in the UK, with 45% of public water suppiies in the Thames Water region derived from subterranean sources. In urban areas. groundwater has been affected by anihropogenic activlties over a long period of time and from a multitude of sources. At present, groundwater quality is assessed using a range of chemical species to determine the extent of contamination. However, analysing a complex mixture of chemicals is timeconsuming and expensive. whereas the use of an ecotoxicity test provides information on (a) the degree of pollution present in the groundwater and (b) the potential effect of that pollution. MicrotoxrM, €cioxrM and Daphnia magna microtests were used in conjunction with standard chemical protocols to assess the contamination of groundwaters from sites throughout the London Borough of Hounsiow and nearby Heathrow Airport. Because of their precision, range of responses and ease of use, Daphnia magna and MicrotoxrM tests are the bioassays that appear to be most effective for assessing groundwater toxicik However, neither test is ideal because It Is also essential to monitor water hardness. EcloxrM does not appear to be suitable for use in groundwaterquality assessment in this area, because it is adversely affected by high total dissolved solids and electrical conductivity.

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A novel biomarker was developed in Daphnia magna to detect organic pollution in groundwater. The haem peroxidase assay, which is an indirect means of measuring oxidase activity, was particularly sensitive to kerosene contamination. Exposure to sub-lethal concentrations of kerosene-contaminated groundwater resulted in a haem peroxidase activity increase by dose with a two-fold activity peak at 25%. Reproduction in D. magna remained unimpaired when exposed to concentrations below 25% for 21 days, and a decline in fecundity was only observed at concentrations above the peak in enzyme activity. The measurement of haem peroxidase activity in D. magna detected sublethal effects of kerosene in just 24 h, whilst offering information on the health status of the organisms. The biomarker may be useful in determining concentrations above which detrimental effects would occur from long-term exposure for fuel hydrocarbons. Moreover, this novel assay detects exposure to chemicals in samples that would normally be classified as non-toxic by acute toxicity tests.