The partitioning, bioavailability, and toxicity of cypermethrin in water-sediment systems was investigated. Cypermethrin adsorbed extensively and rapidly, with an overall mean organic carbon (OC) adsorption partition coefficient (Koc) of 350,000, and approximately 99% adsorption occurred within 24 h. Bioavailability was measured via body burdens of Daphnia magna and Chironomus tentans. Mean biota-sediment accumulation factors (BSAFs), that is, the concentration in the organism as a proportion of the concentration in the sediment, decreased with increasing OC content. The BSAF values were 0.31, 0.14, and 0.08 for D. magna and 0.63, 0.19, and 0.08 for C. tentans, in 1, 3, and 13% OC sediments, respectively. The 10-d median lethal sediment concentrations (LC50s) of cypermethrin were 3.6, 18, and 32 mg/kg for Hyalella azteca and 13, 67, and 62 mg/kg for C. tentans in 1, 3, and 13% OC sediments, respectively. Predictions of aqueous concentrations at the LC50 in sediments (based on Koc) compared well to each other and to effect concentrations from studies in water alone, suggesting that equilibrium partitioning theory could be used reasonably to predict and normalize the toxicity of cypermethrin across sediments of differing OC content.

The partitioning, bioavailability, and toxicity of cypermethrin in water-sediment systems was investigated. Cypermethrin adsorbed extensively and rapidly, with an overall mean organic carbon (OC) adsorption partition coefficient (Koc) of 350,000, and approximately 99% adsorption occurred within 24 h. Bioavailability was measured via body burdens of Daphnia magna and Chironomus tentans. Mean biota-sediment accumulation factors (BSAFs), that is, the concentration in the organism as a proportion of the concentration in the sediment, decreased with increasing OC content. The BSAF values were 0.31, 0.14, and 0.08 for D. magna and 0.63, 0.19, and 0.08 for C. tentans, in 1, 3, and 13% OC sediments, respectively. The 10-d median lethal sediment concentrations (LC50s) of cypermethrin were 3.6, 18, and 32 mg/kg for Hyalella azteca and 13, 67, and 62 mg/kg for C. tentans in 1, 3, and 13% OC sediments, respectively. Predictions of aqueous concentrations at the LC50 in sediments (based on Koc) compared well to each other and to effect concentrations from studies in water alone, suggesting that equilibrium partitioning theory could be used reasonably to predict and normalize the toxicity of cypermethrin across sediments of differing OC content.

The manufacturer's recommended rate for fomesafen in snap beans, dry beans, and soybeans may cause carryover injury in sweet corn. A field experiment, a survey, and multiple greenhouse experiments were conducted to (1) estimate the fomesafen residue concentrations in the soil that might result from use of lower than registered rates, (2) estimate fomesafen residue concentrations in growers' fields and evaluate grower practices for their effects on carryover potential, and (3) investigate the effects of soil type and sweet corn variety on the potential for fomesafen to cause injury to sweet corn. Results of the dissipation study predicted average soil concentrations to be approximately 0.019 mg fomesafen/kg soil at the start of the sweet corn planting season. Half-life values ranged between 28 and 66 d, with an average of 50 d. Residues in grower fields were slightly less than those found in the dissipation study. Injury from fomesafen varied significantly by sweet corn variety and by soil type. Sweet corn grown in soils with high organic matter and low pH were most susceptible to injury from fomesafen. At high rates of fomesafen (0.12 mg/kg), reductions in dry weight of sweet corn varieties ranged from 5 to 60%. At rates of fomesafen slightly higher than those detected in field soils at the time of sweet corn planting (0.03 mg/kg), dry weight either increased slightly (variety trial) or decreased by 6 to 12% (soil-effect trial) depending on soil type. The risk of sweet corn yield losses because of fomesafen carryover appear relatively low. Growers can reduce the risk of carryover injury by planting tolerant varieties in fields where fomesafen was applied the preceding year.

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