This Test Guideline is designed to assess the effects of prolonged exposure of chemicals to the sediment-dwelling larvae of the freshwater dipteran Chironomus sp.

First instar chironomid larvae are exposed to at least five concentrations of the test chemical in sediment-water systems. The test starts by placing first instar larvae into the test beakers containing the sediment-water system and subsequently spiking the test substance into the water. Chironomid emergence and development rate is measured at the end of the test. The maximum exposure duration is 28 days for C. riparius, C. yoshimatsui, and 65 days for C. tentans. Larval survival and weight may also be measured after 10 days if required (using additional replicates as appropriate). The study report should include the development time and the total number of fully emerged midges (sex and number are recorded daily), the observation of any abnormal behaviour, the number of visible pupae that have failed to emerge and any egg masses deposition. The data are analysed either by using a regression model in order to estimate the concentration that would cause x % reduction in emergence, larvae survival or growth, or by using statistical hypothesis testing to determine a NOEC/LOEC.