Earthworm Toxicity and Bioaccumulation of Biosolids-Borne Triclosan (TCS).

The toxicity of a chemical to an organism depends on chemical's bioavailability so total chemical concentration in soils often fails to predict the toxicity or bioaccumulation in an organism accurately. Indeed, toxicity tests are valuable tools for assessing bioavailability and earthworms are ideal organisms for toxicity testing as they live in close contact with soils. We performed bench-top earthworm toxicity and bioaccumulation studies as prescribed by the Office of Chemical Safety and Pollution Prevention (OCSPP) guidelines, to assess biosolids-borne Triclosan (TCS) toxicity and bioaccumulation. A range-finding test suggested no biosolids-borne TCS effect on earthworm mortality up to 10,005 mg TCS kg biosolids^-1 in the Ashkum silty clay loam (ASL) and an artificial soil, but variable effects in the Immokalee fine sand (IFS). Only the IFS soil was utilized in a definitive toxicity study due to the lack of adverse effects in the ASL and artificial soils. There was no TCS treatment effect on earthworm survival at TCS concentrations ≤ 105 mg kg biosolids^-1, and the estimated lethal concentration (LC50) was >105 mg TCS kg biosolids^-1. Besides toxicity, accurate estimates of bioaccumulation factors are critical to conducting ecological and human health risk assessments. An earthworm TCS bioaccumulation study was conducted in IFS and the ASL soils, yielding bioaccumulation factor (BAF) values of 6.52 ± 0.84 in the IFS and 12.7 ± 3.08 in the ASL soils. Biosolids Amended Soil Level IV (BASL4) model calculated BAF values ranged from 2.18-5.02, smaller than our values, and values (10.8-27) reported by others. Our data suggest some TCS accumulation in earthworms, but less than feared by some and more than predicted by fugacity-based models.