Bioavailability of sediment‐sorbed and aqueous surfactants to Chironomus riparius (midge)

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Abstract
The bioavailability of sediment‐sorbed and soluble fractions of three surfactants were compared in egg hatchability and partial life cycle chronic bioassays with the midge Chironomus riparius. The chemicals tested were linear alkyl (dodecyl) benzene sulfonate (LAS), dodecyl trimethyl ammonium chloride (TMAC) and distearyl dimethyl ammonium chloride (DSDMAC). Midge eggs exposed to ranges of surfactant concentrations in water were monitored for hatching success and posthatch survival. No significant reductions in egg hatching were observed at the highest concentrations tested: 18.9 mg/L LAS, 21.5 mg/L DSDMAC and 15.4 mg/L TMAC. Newly hatched larvae were more sensitive than eggs; respective 72‐h LC50 concentrations (48‐h for TMAC) were 2.2, 11.3 and 14.6 mg/L. In partial life cycle chronic bioassays in sediment/water test systems, percentages of winged adults emerging after continuous exposure of larvae and pupae to doses of each surfactant were determined. Exposure concentrations in sediment, interstitial water and overlying water were monitored by 14C liquid scintillation counting. Lowest observed effect concentrations (LOECs) of sediment‐spiked surfactants were 319 to 993 μg/g (dry weight) LAS, 876 to 2,708 μg/g DSDMAC and >3,084 μg/g TMAC (highest concentration tested). Corresponding no observed effect concentrations (NOECs) were 319 μg/g LAS, 876 μg/g DSDMAC and 3,084 μg/g TMAC. The NOECs are approximately 100, 1,000 and 10,000 times greater than respective NOECs of the solubilized materials, and exceed levels of these materials measured in the environment. The results indicated that adsorption onto sediment significantly mitigates surfactant bioavailability to Chironomus.

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