Epsilon Archive for Student Projects

Abstract

Toxicity tests using standardised artificial sediments are a useful tool to evaluate toxicity of pesticides to benthic organisms. Artificial sediments differ from natural sediments in physicochemical characteristics and require feeding of test organisms, which will likely alter the exposure of sediment-associated contaminants and thus the outcome of the test. To determine the potential change in bioavailability, due to sediment physico-chemical characteristics and addition of exogenous food, between artificial and natural sediments, a microcosm study was performed using a standardised methology with the midge-larvae Chironomus riparius. The toxicity of the pesticide lindane was compared in artificial and two natural sediments with the same organic matter content under fed and unfed conditions. Also, feeding rates for C. riparius larvae were determined in two of the test sediments. Neither sediment type (artificial vs. natural) nor the addition of food had effect on the toxicity of lindane as determined by emergence, mean development rate and survival. This shows that the Chironomus test is a robust test that provides a good estimate of contaminant toxicity in natural sediments, despite marked differences in sediment characteristics (e.g. N content, density and water content). However, differences in the lindane concentrations of the overlying water indicated that differences existed in the exposure concentrations of the larvae. By the end of the experiment the concentration of lindane in the overlying water was lower in the microcosms with natural sediments compared with microcosms with artificial sediment. The study also showed that the nutritional value of the artificial sediment is lower compared with the natural sediments despite equal amounts of organic matter. These differences could be due to difficulties for the larvae to explore the artificial sediment due to the realtively high density of the artificial sediment and/or the lower nutritional value of the organic matter pool.