The continuous presence of unknown Salmonella mutagens in XAD-concentrates of Rhine river water has been shown previously. Using nitro-reductase deficient bacterial strains and silica fractionation, it was strongly indicated that the responsible compounds may consist of nitro substituted aromatics (with additional polar groups or heterocyclic structures) and aromatic amines. It was further shown that the same type of mutagens could be detected (104-fold increase) in the bile of rainbow trout exposed to Rhine river water. Considerating the accumulated mutagenic activity in natural occurring fish, this observation argues in favor of a true bioconcentration process of water-borne mutagens in fish bile. The clearance of mutagenic activity of bile after transferring the fish to clean water again is indicative for the importance of biliary excretion of xenobiotics and their metabolites.

A test has been developed to assess the chemically induced disturbance produced by interactions between functionally different groups of organisms. Algae, daphnids, polyps, and decomposer organisms--representing adjacent trophic levels--were housed in separate containers. Water containing algae and nutrients was circulated through the compartments. In some experiments, according to a realistic scheme based on empirically derived knowledge of the needs of the individual populations, an interactive relationship was maintained between standing stock parameters and the circulation rate and between predation on daphnids and feeding by polyps. Since, for each compartment, input and output fluxes were experimentally determined, the rates of processes could be calculated. One of the major drawbacks of the small volume (14 L) of the microcosm was the necessity for nondestructive or micro methods of analysis.

Dit rapport behandelt een nieuwe methode voor het berekenen van het ecologische risico in kavelsloten dat wordt veroorzaakt door het gebruik van een groot aantal bestrijdingsmiddelen (261) in Nederland voor het jaar 1998. De gehele berekening is terug te voeren op een GIS-kaart van het agrarisch landgebruik, waarbij 51 verschillende teelten worden onderscheiden.

How the trophic status of a community can alter the bioavailability and toxic effects of contaminants; Use of Vollenweider-OECD modeling to evaluate aquatic ecosystem functioning; Chemically induced community responses in a compartmentalized microcosm assessed by multidimensional state space transitions; Microbial enzyme activities, potential use for monitoring decomposition processes; Use of microbial colonization parameters as a measure of functional response in aquatic ecosystems; A rapid bioassay using the green alga Selenastrum capricornutum to screen for toxicity in St. Lawrence River sediment elutriates; Effects of complex effluents on photosynthesis in Lake Erie and Lake Huron; State changes in laboratory microecosystems in response to chemicals from three structural groups; An in situ system for evaluating effects of toxicants on the metabolism of littoral communities; Environmental chemicals and biomembranes, kinetics of uptake and influence on membrane functions; Developing a portable automated biomonitoring system for aquatic hazard evaluation; Effects of complex effluents from the river raisin on zooplankton grazing in Lake Erie; Fish behavioral assessment of pollutants; Use of freshwater macroinvertebrates microcosms in the impact evaluation of toxic wastes; Pollution induced community tolerance, a new ecotoxicological tool.