Toxicity characterisation of organic contaminants in stormwaters from an agricultural headwater stream in South East England

The transient movement of pesticides at biologically active concentrations during storm events is considered to be a cause of biological impoverishmen t in some headwater streams. The programme of work described sought to iden tify compounds that are the cause of toxic effects during such events. Alon g with targeted pesticide analysis, toxicity identification evaluation (TIE ) procedures were used to identify compounds with a demonstrated toxic effe ct. These procedures were specifically directed towards isolating and attri buting toxicity to classes of organic contaminants in samples collected fro m an English headwater stream during a storm event. The organic load was is olated by means of solid-phase extraction (SPE). Bioassay of the SPE extrac t at x 100 whole water concentrations confirmed that the samples contained substances toxic to Daphnia magna, although the raw samples were not toxic. Targeted pesticide analysis identified simazine and diuron as the major pe sticides present and, using a toxicity unit (TU) approach, were shown to be responsible for a significant amount of the observed concentrate toxicity during a runoff event. However, they were not present in sufficient quantit ies to be totally responsible for a more toxic later event. By simplificati on of the SPE isolate using reverse-phase HPLC, fractions from which were t ested for toxicity, the cause of concentrate toxicity in the later event wa s isolated to two discrete fractions. GC-MS analysis of these fractions ide ntified nonylphenol, endosulfan sulphate and pendimethalin as present, with the majority of toxicity attributed to nonylphenol (NP). The main advantag e of the TIE approach is that it allows biological active compounds with a demonstrated effect to be identified that may not be selected by more tradi tional techniques. Crown Copyright (C) 2001 Published by Elsevier Science L td. All rights reserved.