Formatted Title:

Development of Methods for Assessing the Toxicity of Sediment-Bound Contaminants with Laboratory-Cultured Mayflies

Background/Objectives:

In freshwater systems at least 60 percent of biodiversity can be composed of aquatic insects. However, species sensitivity distributions on which water quality criteria and risk assessments rely often reflect a paucity of insect data. More research is needed to better understand threats to aquatic insects, including developing more and better laboratory models for evaluating the sensitivity of freshwater insects to emerging contaminants, including those bound to sediments. Among the most used insect species in toxicity testing are midges (Chironomidae), which can be cultured in the laboratory but tend to be among the more insensitive invertebrates. Efforts have been made to assess the potential for use of abundant, wild-caught mayflies (Ephemeroptera) for standardized toxicity test development. However, knowledge of exposure history, health, and age of test organisms before testing provides better interlaboratory test result comparisons. Burrowing mayflies (Hexagenia sp.) are used in sediment toxicity assessments, but these organisms are not cultured continuously in the laboratory and tend to be among the least sensitive taxa in the order Ephemeroptera. In recent years, a parthenogenetic mayfly Neocloeon triangulifer has been shown to be both amenable to continuous culture in the laboratory and particularly sensitive to a variety of waterborne contaminants including metals, major ions, neonicotinoids, and PFAS.

Approach/Activities:

We have developed and improved a system for culturing the required diatom diet for this species. We have also published methods for assessing the acute, short-term chronic, and full-life toxicity of water-borne contaminants. Under pulsed, flow-through conditions regulated by a modified proportional diluter system, we are adapting our methods to contaminated sediment exposures.

Results/Lessons Learned:

Neocloeon triangulifer is a depositional detritus feeder and, therefore well adapted as an epibenthic test organism. Testing this species alongside the burrowing Chironomus sp. and Hexagenia sp. will present an opportunity to explore the effects of contaminants at the sediment surface water interface. Initial efforts involve optimizing test conditions to achieve acceptable levels of control survival and growth. In addition, we are conducting studies with neonicotinoids and PFAS as model chemicals in an effort to develop the sediment bioassay for more broad use across the risk assessment community.

Rebecca Dorman

Affiliation

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(Group 2, Poster Board #16) Development of Methods for Assessing the Toxicity of Sediment-Bound Contaminants with Laboratory-Cultured Mayflies