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Method refinements for the midge life-cycle, Chironomus dilutus test
Citation:
Norberg-King, T., T. Highland, R. Hockett, AND Dave Mount. Method refinements for the midge life-cycle, Chironomus dilutus test. SETAC North America, Salt Lake City, UT, November 01 - 05, 2015.
Impact/Purpose:
not applicable
Description:
Larval stages of non-biting midges can be found in almost any freshwater ecosystem, and one of the commonly tested midges is Chironomus dilutus (Chironomidae, Diptera) which is used for toxicity testing and ecological risk assessment of freshwater contaminants. USEPA, ASTM, Environment Canada, and OECD have published standard methods describing the sediment toxicity tests with various species of midges. USEPA/ASTM’s current guidelines (2000) provide procedures for a midge life-cycle test that begins with newly hatched C. dilutus larva (~1-4 h after hatching free from egg mass). However, since the method was first published, many laboratories have observed wide variability in control survival across tests and many tests have not met the =70% control survival requirement. We are pursuing experiments to better understand the variability in control survival, and to explore techniques that will improve control performance. One line of experimentation is to compare performance of 1-4 h old larvae and 3-4-day old larvae in natural sediment or quartz sand. Previous studies have indicated a difference in sensitivity between <1-h old and 8-d old larvae for certain toxicants; we are interested in whether use of 4-d-old midge might improve typical control survival while retaining some of the greater toxicant sensitivity observed with younger organisms.