Abstract
Acute lethality of Al/Zn/Cu mixtures to fry of American flagfish (Jordanella floridae) was reduced by factors of 2.1 to 14.5 in water of pH 5.8 from four lakes of the Canadian Shield, compared to lethality in synthetic soft water. Test waters ranged from clear to dark brown but were otherwise similar. LC50s for total Al/Zn/Cu were correlated with several measurements of humic substances in the lakes, including total organic carbon (TOC), absorbance at 310 nm (A310), color, and Secchi depth. Dialysis techniques showed that toxicity of Al and Cu was reduced by complexation with high-molecular-weight (MW) (> 1,000) humic substances in the colored water. Zn was present mainly as low-MW forms and effects of complexation on its lethality were not resolved. Regressions predicted that survival of early life-stages of fish is doubtful in acidified, soft-water lakes containing less than 2.2 mg/L of TOC or in which A310 <0.016. Changes in trace-metal lethality associated with TOC were greater than those associated with changes in total hardness.
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