Dissolved organic carbon reduces the toxicity of copper to germlings of the macroalgae, Fucus vesiculosus

This study investigates the effects of waterborne copper exposure on germling growth in chemically defined seawater. Germlings of the macroalgae, Fucus vesiculosus were exposed to a range of copper and dissolved organic carbon (DOC as humic acid) concentrations over 14 days. Germling growth was found to be a sensitive indicator of copper exposure with total copper (TCu) and labile copper (LCu) EC50 values of approximately 40 and 20 μg/L, respectively, in the absence of added DOC. The addition of DOC into the exposure media provided germlings with protection against copper toxicity, with an increased TCu EC50 value of 117.3 μg/L at a corrected DOC (cDOC from humic acid only) concentration of 2.03 mg/L. The LCu EC50 was not affected by a cDOC concentration of 1.65 mg/L or less, suggesting that the LCu concentration not the TCu concentration was responsible for inhibiting germling growth. However, at a cDOC concentration of approximately 2 mg/L an increase in the LCu EC50 suggests that the LCu concentration may play a role in the overall toxicity to the germlings. This is contrary to current understanding of aquatic copper toxicity and possible explanations for this are discussed.