Ing Computacion

Joint effects of temperature and oxygen concentrations for the results of sediment toxicity tests were studied at 10 and 20 ºc with 40% and 80% dissolved oxygen saturation. Growth, feeding rate, andreproduction of lumbriculus variegates (oligochaete) and growth, emergence, and survival of chironomus riparius (diptera) were tested in a polluted and in a reference sediment. Both the feeding ofL. variegates and the emergence of C. riparius were significantly retarded at low temperature. Additionally, differences in the sex ratio of the emerged adults of C. riparius were observed. The oxygenconcentration alone did not have any significant effect on the endpoints, but significant combined effects of polluted sediment and low DD were observed on the biomass of L. variegates. The standardsediment toxicity test might offer only limited data for risk assessment of contaminated sediments at sites where the actual conditions largely differ from laboratory conditions.
1. IntroductionSediment toxicity tests are common approaches to increase weight of evidence in determining whether contamination in any area represented a risk to individual organisms or to the whole ecosystem.Usually, the tests are performed under standardized laboratory conditions to minimise external variation and to insure comparable test results. However, most often the standard test conditions greatlydeviate from the natural conditions in aquatic environment. In the standardised sediment toxicity tests with benthic invertebrates, the temperature recommendations range from 20 to 23ºc, and aerationis recommended if oxygen level in the sediment overlying water drops below 2.5 mg/1 or below 60% saturations. In the cold temperature region, water temperature seldom teaches 20 ºc even in summer andthe sediment surface can become hypoxic or even anoxic during the stratification periods. For the risk assessment of polluted sediments, it would be valuable to know the combined effects of natural...