EFFECTS OF DISSOLVED ORGANIC-CARBON ON ACCUMULATION AND ACUTE TOXICITY OF FENVALERATE, DELTAMETHRIN AND CYHALOTHRIN TO DAPHNIA-MAGNA (STRAUS)

The effects of dissolved organic carbon (DOC) in the form of Aldrich humic acid on the accumulation and acute toxicities of three synthetic pyrethroids - fenvalerate, deltamethrin, and cyhalothrin - to Daphina magna in laboratory experiments were investigated. Concentrations of DOC as low as 2.6 mg/L, 3.2 mg/L, and 3.1 mg/L for deltamethrin, fenvalerate, and cyhalothrin, respectively, resulted in a significant decrease in bioaccumulation. Acute toxicities of all three pyrethroids were found to decrease as DOC concentrations increased; e.g., at a DOC concentration of 15.5 mg/L, the acute toxicity of fenvalerate was reduced by a factor of 17. The percentages of deltamethrin and fenvalerate bound to DOC increased as DOC concentrations increased after 2-h and 24-h contact times. At low concentrations of DOC (e.g., 1.7 mg/L), as much as 40% of fenvalerate and 20% of deltamethrin were found sorbed to the dissolved material. After 24-h contact times, 76.4 and 80.8% of fenvalerate and deltamethrin, respectively, were bound to DOC. Reverse-phase partition coefficients (K(rp)) for both fenvalerate and deltamethrin were found to vary with DOC concentrations and were in the range 1.0 to 4.8 x 10(5) L/kg for fenvalerate and 0.9 to 5.6 x 10(5) L/kg for deltamethrin.