Toxicity of permethrin to Chironomus riparius in artificial and natural sediments

Standard sediments are required for prospective risk assessments so that comparable fate and effects data can be generated within and between laboratories. One approach is to use artificial media that can be easily reproduced and characterized. However, a concern is that these media may not simulate natural sediments in terms of binding and toxicological properties, In this study, the acute and chronic effects of permethrin were compared in two artificial and one natural sediment using larvae of the midge Chironomus riparius. The influence of clay and carbon content and organic matter type on permethrin toxicity was also investigated. The toxic response measured in natural sediment was lower than that in the two artificial sediments, one of which contained peat and the other which contained alpha-cellulose as the organic carbon source. Of the two, the peat-based medium gave a more comparable response to the natural sediment. Acute and chronic permethrin toxicity was influenced by all sediment factors investigated with a consistently lower toxicity measured in the peat-based sediment compared with the a-cellulose sediment. A decrease in toxicity. coupled with an increase in bulk sediment permethrin concentration, was seen as both clay and organic carbon contents increased. Consideration should be given to improving the environmental realism of simple artificial formulations if the intention is to represent effects measured in natural sediments.