Publication Abstract

Toxicity characterisation of organic contaminants from an agricultural headwater stream in south east England

K.V. Thomas, M.Hurst, P. Matthiessen, D. Sheahan and R. Williams

The transient movement of pesticides at biologically active concentrations during storm events is considered to be a cause ofbiological impoverishment in some headwater streams. The programme ofwork described sought to identify compounds that are the cause oftoxic effects during such events. Along with targeted pesticide analysis, toxicity identification evaluation (TIE) procedures were used to identify compounds with a demonstrated toxic effect. These procedures were specifically directed towards isolating and attributing toxicity to classes of organic contaminants in samples collected from an English headwater stream during a storm event. The organic load was isolated by means of solid phase extraction (SPE). Bioassay ofthe SPE extract 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 maj or pesticides present and, using a toxicity unit (TU) approach, were shown to be responsible for a significant amount ofthe observed concentrate toxicity during a runoffevent. However, they were not present in sufficient quantities to be totally responsible for a more toxic later event. By simplification ofthe SPE isolate using reverse phase HPLC, fractions from which were tested for toxicity, the cause of concentrate toxicity in the later event was isolated to two discrete fractions. GC-MS analysis ofthese fractions identified nonylphenol, endosulfan sulphate and pendimethalin as present, with the majority oftoxicity attributed to nonylphenol (NP). The main advantage ofthe TIE approach is that it allows biological active compounds with a demonstrated effect to be identified that may not be selected by more traditional techniques.

Reference:

K.V. Thomas, M.Hurst, P. Matthiessen, D. Sheahan and R. Williams, 2001.oxicity characterisation of organic contaminants from an agricultural headwater stream in south east England.Water Research, 35(10): 2411-2416