Chronic Toxicity of Iron to Aquatic Organisms under Variable pH, Hardness, and Dissolved Organic Carbon Conditions

摘要

A series of chronic toxicity tests was conducted exposing three aquatic species to iron (Fe) in laboratory freshwaters.The test organisms included the green algae Raphidocelis subcapitata, the cladoceran Ceriodaphnia dubia, and thefathead minnow Pimephales promelas. They were exposed to Fe (as Fe (Ⅲ) sulfate) in waters under varying pH (5.9–8.5),hardness (10.3–255 mg/L CaCO3), and dissolved organic carbon (DOC; 0.3–10.9 mg/L) conditions. Measured total Fe wasused for calculations of biological effect concentrations because dissolved Fe was only a fraction of nominal and did notconsistently increase as total Fe increased. This was indicative of the high concentrations of Fe required to elicit a biologicalresponse and that Fe species that did not pass through a 0.20‐ or 0.45‐μm filter (dissolved fraction) contributed to Fe toxicity.The concentrations frequently exceeded the solubility limits of Fe(III) under circumneutral pH conditions relevant to mostnatural surface waters. Chronic toxicity endpoints (10 effect concentrations EC10s) ranged from 442 to 9607 μg total Fe/Lfor R. subcapitata growth, from 383 to 15 947 μg total Fe/L for C. dubia reproduction, and from 192 to 58,308 μg total Fe/Lfor P. promelas growth. Toxicity to R. subcapitata was variably influenced by all three water quality parameters, but especiallyDOC. Toxicity to C. dubia was influenced by DOC, less so by hardness, but not by pH. Toxicity to P. promelas was variable,but greatest under low hardness, low pH, and low DOC conditions. These data were used to develop an Fe‐specific,bioavailability‐based multiple linear regression model as part of a companion publication.