Development and application of bioassays for a site-specific risk assessment of contaminated soil

Abstract

Soil risk assessment based on generic approaches is accompanied by a large number of uncertainties. In site-specific risk assessment aimed at identifying the actual effects on the ecosystem by using e.g. bioassays in soil elutriates and taking into account land-use these uncertainties can be largely reduced. In this thesis the application and development of bioassays for a site-specific risk assessment of contaminated soil has been discussed. The first part of this thesis deals with the influence of storage on the water extractable ecotoxicological potential of contaminated soils. It is investigated whether microbial turnovers and losses of volatile organic compounds are the main cause for storage-dependent changes in soil samples. The investigations show that the oxygen consumption depends on the storage temperature, organic matter content, nutrient content, and total content of toxic substances. A flow scheme is derived that can be a useful tool for a sequential ap proach to determine the storage capacity for toxicological investigations. Furthermore, recommendations are given under which circumstances soil samples should ideally be stored. The second part of this thesis covers the investigations dealing with the application and validation of bioassays for risk assessment and remediation control. The by DECHEMA recommended bioassays for soils were used to investigate six contaminated soil samples. The test results demonstrate that toxic contaminants are present and bioavailable in water elutriates from two soils. Following up on this a laboratory intercomparison study is performed to determine the validity of miniaturized biological test systems. The toxicological assessment of the soil samples in this study show a high degree of uniformity between the different laboratories. It is further concluded that for the assessment different bioassays are needed. In the last study of this part soil samples were investigated before and after remediation us ing chemical and toxicological analyses. Remediation of main pollutants did in general not lead to a risk reduction of the water-extractable ecotoxic and genotoxic potential. It is concluded, that the assessment and remediation of contaminated sites without consideration of biological test systems is not sufficient. In the last part of this thesis a stepwise approach to investigate the habitat function of soils using respirometry is described. It is demonstrated that a stepwise addition of carbon, nitrogen, and phosphorus enables a distinction between growth-promoting effects of biodegradable organic compounds on the one hand and the toxic influence of these compounds on the other hand. Overall it is concluded that the biological quality of a soil cannot be predicted using only chemical concentrations. It is therefore feasible to extent the assessment based on chemical methods with biological methods. Based on the work in this thesis guidance on the choice and evaluation of tests appli ed for ecotoxicological characterization of soils and soil materials is given in ISO standard 17616. The recommended tests can also be used for a quick on-site analysis, as the actual performance is highly automised, and evaluation criteria have been established.