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Refining methods for conducting long-term sediment and water toxicity tests with Chironomus dilutus: Formation of a midge chronic testing work group
Citation:
Ingersoll, C. AND Dave Mount. Refining methods for conducting long-term sediment and water toxicity tests with Chironomus dilutus: Formation of a midge chronic testing work group. SETAC North America, Salt Lake City, UT, November 01 - 05, 2015.
Impact/Purpose:
not applicable
Description:
Standard methods have been established by USEPA, ASTM International, Environment Canada and Organization for Economic Cooperation and Development for conducting sediment toxicity tests with various species of midges including Chironomus dilutus. Short-term 10-day exposures are typically started with second to third instar larvae (e.g., about 7- to 10-day old) measuring effects on survival, weight, and biomass. Long-term ~50-day exposures are typically started with first instar larvae (e.g., <1- to <2-day old) measuring effects on larval survival, weight, biomass and adult emergence and reproduction including hatching of offspring. Laboratories routinely meet test acceptability criteria (TAC) for short-term exposures (e.g., 10-day control larval survival >70% and ash-free-dry weight >0.48 mg/individual). However, laboratories report difficulty meeting TACs for long-term exposures (e.g., 20-day control larval survival >70% or adult emergence >50%). Based on the success of a Hyalella azteca (Amphipod) Testing Work Group started in 2010, a Midge Chronic Testing Work Group (MCTWG) was started in 2015 with representatives from 9 laboratories experienced with conducting long-term midge exposures (USGS Columbia MO; USEPA Duluth MN; USACE Vicksburg MS; Smithers Vincent Warehem MA; Wildlife International Easton MD; Nautilus Environmental Burnaby BC; UC Davis CA; Syngenta Raleigh NC; University Guelph Ontario). Topics being addressed by the MCTWG include: (1) Starting age of test organisms (e.g., improved performance starting toxicity tests with 3- to 4-day old larvae rather than starting with < 2-day old larvae); (2) Primary toxicity endpoints (e.g., identify a subset of chronic endpoints most responsive to toxicants); (3) Feeding (e.g., ramped ration during exposure); (4) Starting age for 10-day testing (e.g., perhaps starting with 3- to 4-day old larvae); (5) Replication of reproductive endpoints (e.g., reduced number of replicates or auxiliary male beakers); and, (6) Inter-laboratory testing (e.g., once methods have been refined to improve control performance in chronic water or sediment toxicity testing). Example data sets will be provided on the ongoing efforts by the MCTWG to refine midge chronic methods. Outcomes of these efforts will be used to guide ongoing revisions to USEPA and ASTM methods for conducting sediment toxicity tests or water toxicity tests with C. dilutus and H. azteca.