The potential for oestrogenic effects of pesticides in headwater streams in the UK.

Twenty-six pesticidal compounds and samples of stormwater from two different agricultural catchments were screened for oestrogenic activity using an in vitro recombinant yeast-based assay. Only six fungicides showed an oestrogenic response with low comparative biological activity of 5000 to 2.5 million times less potent than 17beta-estradiol (E2), a natural steroidal oestrogen. Concentrations of biological activity expressed as E(2) equivalents for the headwater stream stormwater samples ranged from <0.01 to 0.11 ng E2/l. These values are at least one order of magnitude below levels that have been documented to produce oestrogenic effects in fish and are therefore considered to represent a low risk to associated headwater stream communities. The potential sources of the oestrogenic activity measured in the headwater streams are discussed.