Abstract
Iron is a common pollutant in waters near coal and hard rock mine disturbances. The current 1000 µg/L total recoverable chronic criterion for iron (Fe) for protection of aquatic life in the United States was developed using very limited data in 1976 and has not been revised since. To develop a more scientifically based criterion, several chronic laboratory toxicity experiments (> 30 days) were conducted with ferric Fe at circumneutral pH on a taxonomically diverse group of organisms including brown trout (Salmo trutta), mountain whitefish (Prosopium williamsoni), boreal toad tadpoles (Bufo boreas), the oligochaete worm Lumbriculus variegatus, the mayfly Hexagenia limbata, and the planarian Dugesia dorotocephala. Results of these tests and those of previously published toxicity data were used to derive a Final Chronic Value (FCV) of 499 µg/L by using the US Environmental Protection Agency’s recommended methods based on single species toxicity tests. In addition to single species toxicity tests, ferric Fe toxicity experiments (10 days) were performed on mesocosms containing naturally colonized communities of benthic macroinvertebrates. Fourteen genera in the mesocosms occurred at sufficient densities to estimate an iron concentration resulting in 20% reduction in abundance (EC20). Three of these taxa had EC20s less than the FCV of 499 µg/L derived from single species tests: the mayfly Epeorus sp. (335 µg/L), the caddisfly Micrasema sp. (356 µg/L), and midge Tanytarsini (234 µg/L). When mesocosm results were included, the FCV was lowered to 251 µg/L. These findings support the suggestion that modernization of water quality criteria should include data generated from mesocosm experiments and other lines of evidence.
Highlights
Iron is abundant in the earth’s crust and occurs naturally in the aquatic environment; concentrations can be elevated due to human activities
To test the hypothesis that our Final Chronic Value (FCV) derived from single species tests is protective of natural benthic communities, EC20 values from the mesocosm study were compared to the FCV
Single species toxicity tests were deemed acceptable based on ASTM criteria (1997)
Summary
Iron is abundant in the earth’s crust and occurs naturally in the aquatic environment; concentrations can be elevated due to human activities. With these toxicity test results, iron toxicity data are available for a sufficiently diverse array of organisms to meet USEPA’s recommended methods to calculate a chronic final value (FCV) for total Fe. Traditionally, results from single species toxicity tests are used exclusively to derive U.S water quality criteria. To test the hypothesis that our single-species derived FCV was protective, we conducted a 10 day mesocosm experiment using naturally colonized communities of benthic macroinvertebrates.
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