Petroleum substances enter the environment, where they cause its degradation. Contamination has an adverse effect on the protective function of soil and soil physicochemical properties, leading to disorders in the soil enzymatic activity, depressing soil fertility and impairing the growth, development and chemical composition of plants. We should therefore look for methods which will enable us to reduce the effect of petroleum substances or even to recover the original properties of soil. The objective of the present study has been to determine the effect of substances applied to soil on the content of cadmium, lead, chromium and manganese in soil contaminated with incremental doses of heating oil (0-20 g kg(-1) of soil). The effect of incremental doses of heating oil on the content of analyzed trace metals in soil was varied and depended on the application of alleviating substances to soil. The increasing levels of heating oil contributed to a decrease in the content of cadmium and chromium in soil, but had no such regular influence on the content of lead or manganese. None of the applied alleviating substances had a reducing effect on the content of manganese, cadmium, chromium or lead in the tested soil. Zeolite was an exception in that it reduced the content of cadmium and lead in soil. The content of heavy metals in soil, even when contaminated with the highest doses of heating oil, did not exceed the permissible levels defined in the Regulation of the Ministry of the Environment of 9 September 2002 and therefore allowed us to classify the soil as a zero contamination degree according to the IUNG Pulawy classification.
