Comparisons of terrestrial and aquatic bioassays for oil-contaminated soil toxicity

Abstract

Petroleum products are widely used in various sections of industry and they are one of the most abundant sources of environmental contamination. These products are classified by their physico-chemical properties such as boiling point, density and viscosity. Oil contamination in the environment is primarily evaluated by measuring the chemical concentrations of petroleum products in the solid or water phase. The results of chemical analyses do not correspond directly with the harmful environmental effects of petroleum products on the soil flora and fauna, because the interactions between oil compounds and the production of their methabolites in soil are not measured in chemical assessments. These kinds of effects of complex chemical mixtures in soil can be estimated by bioassays. Therefore, ecotoxicological tests are important for estimating soil quality in the risk assessment of oil-contaminated soil sites. The objective of this study was to examine the oil-contaminated soil site of a closed petrol station with both chemical and ecotoxicological methods. The goals of this study were to compare the sensitivity of the terrestrial and aquatic bioassays and to compare the toxicity responses of aquatic bioassays determined from three different extraction procedures. In addition, our aim was to characterise a cost-effective battery of bioassays that could be applied to a comparison of oil-contaminated soils. It was in our interest to investigate oil-contaminated soil with oil concentrations of 2500–12000 mg/kg and to find out the possible differences between terrestrial and aquatic toxicity tests. Six soil samples from a closed petrol station were examined for toxicity with terrestrial and aquatic tests. Terrestrial tests includedEnchytraeus albidus survival and reproduction assays and seed germination assays using wheat, cress, lettuce, and red clover seeds and growth inhibition assays of onions. The toxicities of the water-extractable fractions of the soil samples obtained from three different extractions were tested with aquatic bioassays based on plants (onion and duckweed growth inhibition tests), microbes (luminescent bacteria test), and enzyme inhibition (reverse electron transport test, RET). Chemical analyses of the solid samples were carried out simultaneously. Results. Oil concentrations ranged from 2500 to 12000 mg/kg, BTEX varied from 300 to 2800 mg/kg, and fuel additives: MTBE and TAME from 0.0 1 to 260 mg/kg. Only the sample contain-ing 12000 mg/kg oil had a significant toxic impact on all test organisms. Soil samples with oil concentrations 2500–6200 mg/ kg had no or only slight adverse effects on the test organisms with one exception, theE. albidus reproduction test. TheE. albidus survival and reproduction tests were the most sensitive bioassays of the terrestrial tests, and the luminescent bacteria test of the aquatic tests.