Uptake and elimination of triorganotin compounds by larval midge Chironomus riparius in the absence and presence of Aldrich humic acid

Sediments contaminated with triorganotin compounds (TOTs) are abundant in a reas with high shipping activities. In such areas, sediment dwellers such a s chironomids may introduce these very toxic contaminants into foodwebs. In this work, we studied systematically the uptake and elimination of tributy ltin (TBT) and triphenyltin (TPT) with larvae of Chironomus riparius at pH 5 and pH 8 and in the absence and presence of Aldrich humic acid (AHA). Bot h uptake and elimination data could be simultaneously fit by a two-pool mod el, and uptake, excretion, and metabolism rate constants could be derived w ith very :, good reproducibility. Bioconcentration was found to be signific antly lower for TBT than for TPT, although TBT is more hydrophobic. The maj or reason was the rapid metabolism of TBT to dibutyltin (DBT) and further t o monobutyltin (MBT). Apparent AHA-water distribution ratios (D-AHA) were d erived from bioconcentration experiments in the presence of AHA and were co mpared with D-AHA values determined in dialysis experiments. Except for som e explainable discrepancies, a good agreement between both sets of D-AHA va lues was found, confirming the hypothesis that TOTs associated with AHA are not bioavailable. The results of this work demonstrate that chironomids ar e well-suited organisms to study the speciation and bioconcentration of org anotin compounds present in sediment pore waters.