title: Interacting effects of toxicants and organic matter on the midge Chironomus riparius in polluted river water.
abstract: Toxicants and organic matter in river water have contrasting impacts on macrofauna. Through manipulations of both factors, their interactive effects on organisms were evaluated. This way, an attempt was made to clarify the presence or absence of pollution-"tolerant" and -"sensitive" species in rivers affected by mixed sources of pollution. Under controlled conditions, larval growth of the "tolerant" midge Chironomus riparius was measured in different types of river water containing varying levels of particles (obtained by selective filtration) and toxicants (either complex mixtures or metals). Exposure of first-instar larvae to water from the polluted rivers Meuse and Dommel revealed that growth was less inhibited by toxicant levels in river water than expected based on laboratory toxicity tests. Factors present in polluted river water stimulated growth of midges to such an extent that inhibiting effects of high toxicant concentrations were neutralized, and at low toxicant levels, were overcompensated for. It was found that particulate matter has great potential to reduce inhibiting effects of toxicants on C. riparius, not (only) by reducing the bioavailability of toxicants, but by serving as a supplementary, superior food source. The success of the "pollution-tolerant" midge was not explained by tolerance of this species to toxicants, but by its ability to take advantage of coinciding organic enrichment. It is hypothesized that the extent to which beneficial effects of organic compounds on organisms occur is species specific.
authors.affiliation: Department of Aquatic Ecology and Ecotoxicology, ARISE, University of Amsterdam, Kruislaan 320, 1098 SM Amsterdam, The Netherlands.
authors.forename: S C
authors.initials: SC
authors.lastname: Stuijfzand
authors.forename: M
authors.initials: M
authors.lastname: Helms
authors.forename: M H
authors.initials: MH
authors.lastname: Kraak
authors.forename: W
authors.initials: W
authors.lastname: Admiraal
mesh_terms: D000818:Animals; D002683:Chironomidae / Q000187:drug effects*; D005618:Fresh Water / Q000737:chemistry; D008670:Metals / Q000633:toxicity*; D013045:Species Specificity; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*
chemical_list: D008670:Metals; D014874:Water Pollutants, Chemical