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 areas with high shipping activities. In such areas, sediment dwellers such as chironomids may introduce these very toxic contaminants into foodwebs. In this work, we studied systematically the uptake and elimination of tributyltin (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). Both uptake and elimination data could be simultaneously fit by a two-pool model, and uptake, excretion, and metabolism rate constants could be derived with very good reproducibility. Bioconcentration was found to be significantly lower for TBT than for TPT, although TBT is more hydrophobic. The major reason was the rapid metabolism of TBT to dibutyltin (DBT) and further to monobutyltin (MBT). Apparent AHA−water distribution ratios (D AHA) were derived from bioconcentration experiments in the presence of AHA and were compared with D AHA values determined in dialysis experiments. Except for some explainable discrepancies, a good agreement between both sets of D AHA values was found, confirming the hypothesis that TOTs associated with AHA are not bioavailable. The results of this work demonstrate that chironomids are well-suited organisms to study the speciation and bioconcentration of organotin compounds present in sediment pore waters.