Using Hexagenia in sediment bioassays: methods, applicability, and relative sensitivity.

Area of Science:

• Environmental toxicology
• Aquatic invertebrate research

Background:

• Standardized species like Hyalella azteca, Chironomus dilutus, and Lumbriculus variegatus dominate sediment toxicity testing.
• Hexagenia sp. offers unique advantages as a supplemental organism due to its sensitivity, long aquatic life stage, and large body size.

Purpose of the Study:

• To present a standardized method for collecting, hatching, and culturing Hexagenia nymphs for toxicity testing.
• To evaluate the relative sensitivity of different Hexagenia size classes to bifenthrin.
• To establish sublethal toxicity endpoints for Hexagenia.

Main Methods:

• Detailed protocols for Hexagenia egg collection, hatching, nymph rearing, and toxicity testing.
• Comparative toxicity analysis using bifenthrin across three Hexagenia size classes.
• Determination of median lethal concentrations (LC50) and sublethal endpoints (immobilization, suspended solids).

Main Results:

• Hexagenia demonstrated sensitivity to bifenthrin, with varying responses across size classes.
• Established median lethal concentrations for Hexagenia were compared to Hyalella and Chironomus.
• Sublethal endpoints, including immobilization and suspended solids, were successfully defined for Hexagenia.

Conclusions:

• Hexagenia sp. is a viable and sensitive species for sediment toxicity and bioaccumulation assessments.
• The outlined methods provide a framework for incorporating Hexagenia into routine toxicological bioassays.
• This research supports the expanded use of Hexagenia in environmental risk assessments.