The OECD guideline for measuring adsorption-desorption was applied. The guideline was found to be adequate for determining the equilibrium distribution in adsorption studies, but not the sorption/desorption kinetics for very rapidly sorbing substances. The recently developed guidelines for studying biodegradation under environmentally realistic conditions were applied.
Two laboratories performed biodegradation tests. The results from the two laboratories were different for the hydrophobic pesticide pendimethalin, whereas similar results were obtained for the less hydrophobic pesticides ioxynil and bentazone.
Test concentrations, sediment characteristics and the source of the water seem to influence the results.
Hydrophobic pesticides will be transported into the sediment phase in natural water systems consisting of a water layer above a sediment phase.
New methods for studying the uptake into and bioaccumulation of the chemicals in the test organisms and new methods of studying the toxicity of chemicals in a system with a water layer above a sediment phase were developed and applied. It was shown that the presence of sediment and the characteristics of the sediment influence the observed toxicity.