Ecotoxicological assessment of drill cuttings of oil deposits by biotesting methods

Abstract

Complex multi-component wastes include sewage sludges of treatment plants, industrial and domestic wastes, as well as drill cuttings. In the oil-producing regions, they are the main large-capacity waste. Chemical composition of drill cuttings is conditioned by mineralogical composition of drilled solids and properties of chemicals used in drilling. Since the composition of the latter is not always known (in some cases it can be protected by patent), it is almost impossible to establish the danger or safety of drill cuttings to the environment, based only on the use of chemical analysis methods. Therefore, the only way allowing to assess the cumulative toxicity of drilling waste is biotesting which is based on the determination of reaction of the living organisms to content of the pollutant in the tested sample.

While assessing the toxicity of drill cuttings by biological methods, scientists often test the aqueous extract to which the soluble forms of pollutants tend to migrate (eluate biotesting method), and various hydrobionts are used as the tested organisms. However, for adequate assessment of multicomponent solid mediums apart from the eluate methods, it is necessary to use substrate biotesting that provides direct contact of test organism with the tested sample, and thus allows to establish the level of cumulative impact rendered by the contaminants present in the solid substrates, on the living organisms. Therefore we, especially for the purpose of drill cuttings evaluation, have developed substrate methods in which higher plants and natural complex of microorganisms contained in the sludge itself are used as the tested organisms.

The goal of our researches was ecotoxicological assessment of drill cuttings in the oil fields of the Western Siberia, applying methods of substrate and eluate biotesting. For this purpose, test organisms at various levels of organization were used: microorganisms, aquatic organisms, higher plants, and mammals.

It has been established that the studied drill cuttings are hypotoxic or practically nontoxic. According to current statutory regulations of the Russian Federation, they can be classified within IV and V hazard classes. The results of the conducted researches indicate the advisability of applying, for the purpose of environmental assessment of drill cuttings, of both eluate and substrate biotesting methods.