AN EVALUATION OF 4 TYPES OF FRESH-WATER MODEL ECOSYSTEM FOR ASSESSINGTHE HAZARD OF PESTICIDES

Experimental results are reported on four types of freshwater model ec osystem after administration of a single dose of chlorpyrifos. The fat e, and primary and secondary effects of chlorpyrifos were compared bet ween the model ecosystems, and were evaluated in the light of the pred ictive value of the current ecotoxicological hazard assessment procedu re for pesticides, `Slootbox', a fate model used in the ecotoxicologic al risk assessment of pesticides in the Netherlands, overestimated chl orpyrifos concentrations, The primary effects of chlorpyrifos can be p redicted accurately on the basis of single species laboratory toxicity data. The population effects observed in the microecosystems, microco sms, and mesocosms were consistent between all experiments and with th e single species tests, Community metabolism, as a functional endpoint , was less sensitive than the structural parameters measured, Secondar y effects, both for structural and functional endpoints, varied betwee n the micro- and mesocosm experiments. At the present 'state of the ar t' in ecotoxicology, no a priori prediction of secondary effects in na tural ecosystems will generally be possible. 0.1 times the lowest acut e L(E)C-50 for chlorpyrifos, as measured in the current ecotoxicologic al hazard assessment procedure, matched the NOEC(mesocosm) for a singl e dose of chlorpyrifos, Recovery of populations affected by insecticid e stress was found to depend on factors such as life cycle characteris tics and ecological infrastructure, in addition to the toxicant concen tration. The onset of (potential) recovery is likely to start at an ap proximate concentration of the EC(10)(48 h).