USEPA and ASTM sediment and water toxicity methods for H. azteca and C. dilutus: Draft guidance for control test acceptability and historic performance

USEPA and ASTM developed the first standard methods for conducting laboratory sediment toxicity tests in the 1980s and 1990s. A work group is currently developing revised guidance to those sediment methods for conducting 10-d and long-term reproductive exposures with the amphipod Hyalella azteca and the midge Chironomus dilutus. The revisions focus on: (1) Increasing food rations provided during an exposure, (2) Chemical constituents of reconstituted water (for H. azteca), (3) Starting age or size of test organisms, (4) Use of a biomass endpoint, (5) Testing replicates for chemistry analyses, (6) Use of a sand control to establish quality of water and food; (7) Equilibration of sediments in the exposure beakers, (8) Water-only toxicity testing methods, (9) Updated test acceptability criteria (TAC) for an individual test, and (10) Proficiency guidelines for repeated testing by an individual laboratory. Draft revised TAC for controls include accept-able minimum values for: (1) Ending survival, (2) Proportional increase in ending weight (H. azteca), (3) Ending larval weight (C. dilutus), (4) Percent emergence of adults (C. dilutus), and (5) Various reproductive endpoints. Draft proficiency guidelines for repeated testing of historic controls are also being established for these same five values (e.g., nine tests conducted over the past three years with the same control material). The laboratory proficiency guidelines will likely be provided as “minimum” and “mean” per-formance levels. Minimum descriptors reflect performance that laboratories should only rarely fail to meet, while mean descriptors reflect performance that should be typical. Across multiple tests, control performance above TAC should be expected from a laboratory proficient with the methods. If the typical performance of a laboratory is not substantially above minimum TAC, it may be indicative of underlying problems with laboratory facili-ties, practices, or experience. Importantly, the proficiency guidelines are not intended for use in judging validity of an individual test. Instead, these proficiency guidelines should be used to demonstrate overall laboratory capability to repeatedly conduct a valid toxicity test.