R7 AM Soil Ecotoxicology and Risk Assessment
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in 327-329

(ROE-1117-660815) Soil properties affect the toxicity of tributyltin-oxide (TBT-O) to earthworms, springtails, and plants.

Roembke, J.¹, Jaensch, S.¹, Junker, T.¹, Pohl, B.¹, Scheffczyk, A.¹, Schallnass, H-J.¹, ¹ ECT Oekotoxikologie GmbH, Floersheim, Germany

ABSTRACT- Environmental risk assessment of chemicals in the soil relies mainly on tests with OECD artificial soil. Chemical bioavailability in artificial soil can contrast with bioavailability in natural soils and produce ecotoxicological results that are not representative of species exposure conditions in the field. We initially evaluated reproduction and growth of earthworms and collembolans, and early seedling growth of a dicotyledonous plant species in nine natural soils, having a wide range of physico-chemical properties, and in OECD soil. Soils that supported reproduction and growth of the test species were than used to investigate the toxicity of the biocide tributyltin-oxide. Interim results showed that natural soils sustained greater toxicity of TBT-O to earthworms (EC50 values varied from 0.5 to 4.7 mg/kg soil dry weight (DW)) compared with toxicity in OECD soil (EC50 = 13.4 mg/kg DW). Collembolans were less sensitive to TBT-O than earthworms in natural soils with EC50 values ranging from 23.4 to 177.4 mg/kg DW. In contrast with earthworms, the toxicity of TBT-O to collembolans in OECD soil (EC50 of 104.0 mg/kg DW) was within the range of EC50 values established for natural soils. Phytotoxicity tests revealed even greater difference between the exposure effects in natural soils (EC50 ranged from 5.4 to 189.2 mg/kg DW) and in OECD soil (EC50 of 535.5 mg/kg DW) when compared with results of the earthworm tests. Our data also show that EC50 values were more robust endpoint compared to EC10 values based on comparisons of coefficients of variation. These preliminary results show that toxicity testing should include studies with natural soils in addition to OECD soil to better reflect the exposure in the field. Alternatively, the inclusion of a safety factor may be recommended for risk assessment to adjust the EC50 values established in artificial soil thus insuring a better protection of soil organisms.

Key words: biocide, laboratory test, field soils