Method of ecological assessment of oil-contaminated soils

Abstract

A method for determination of the ecological condition of oil-contaminated soils was developed. This method is suitable for use in a wide range of oil concentrations in soil, ranging from 0–20% and provides a quantitative assessment of phytotoxicity – effective toxicity. The method involves the germination on the investigated soil (moisture 33.3%) in closed Petri dishes in the dark at +24ºС of seeds of test objects: Linum usitatissimum L., Helianthus annuus L., Fagopyrum vulgare St. We used for biotesting initial growth parameters of test objects during 5 days of growth, whenthe toxic effect of oil is quite evident, but other damaging factors do not become apparent. For each test object, an optimal oil concentration range is suggested. At low concentrations of oil in the soil <1% it is appropriate to use F. vulgare, at higher concentrations 1.0–2.5% –L. usitatissimum, H. annuus; 10.0–15.0% –L. usitatissimum, F. vulgare; for intervals 2.5–10.0% 15.0–17.0% application of each of three plant species is possible: L. usitatissimum, H. annuus, F. vulgare. We proved that the best estimate of toxicity is possible on the basis of the value of effective toxicity (Tef). The linear relationship between concentration of oil in the soil and Tef is established. Effective toxicity was calculated for any of the proposed test objects and joint use of them will increase the accuracy of research. Effective toxicity characterizes the total impact of toxicants on the growth parameters of plant test-objects and is calculated as the sum of factors inhibiting germination, growth of root and shoot minus the number of recorded parameters. The total assessment of toxicity is based on phytotoxicity which is equal to effective toxicity on L. usitatissimum, H. annuus, and a half of effective toxicity on F. vulgare. A scale of toxicity of oil-contaminated soils is suggested, which shows the relationship between phytotoxicity, content of oil in soil and pollution level. It is established that for the soils polluted by oil with concentration <0.4%, phytotoxicity is <0.6, and the level of pollution is characterized as admissible. If the concentration of oil in the soil is 0.4–2.5%, phytotoxicity is 0.6–1.5; the level of pollution – threatening. If the oil concentration in the soil is 2.5–10.0%, phytotoxicity is 1.5–3.0; pollution level – pre-crisis. For soils polluted by oil at the level 10.0–15.0% phytotoxicity – 3.0–4.0; pollution level – crisis, and for soils with oil concentration >15.0% phytotoxicity is >4.0; the level of pollution – catastrophic. The method was tested on an industrial area – dumps of the Borislav Ozokerite Mine. Environmental maps of toxicity drawn up using different test objects: L. usitatissimum, H. annuus, F. vulgare were similar, which additionally confirms the correctness of the method. We recommend the application of the proposed method for identification of sites in a threatening, pre-crisis or crisis state, on which other physical-chemical studies can be further conducted.