Ecotoxicological testing of soil by four bacterial biotests

Abstract

The objective of this work was threefold. Firstly, this paper intends to introduce four microbial toxicity screening methods (Bacillus subtilis agar diffusion method, Azotobacter agile and Pseudomonas fluorescens dehydrogenase enzyme inhibition tube test, and Photobacterium phosphoreum contact toxicity test) for the investigation of contaminated solid samples such as soil and sediment. Secondly, this work was carried out to prove that both soil characteristics and chemical form of contaminants influence the bioavailability of contaminants and alter the toxicity of soil sample considerably. Thirdly, the sensitivity of the above mentioned four biotests to different contaminants of the soil (heavy metals, organic compounds) was determined and compared. The data evaluation was processed by computer aided statistical methods such as cluster, correlation and principal components analysis by the use of StatgraphicsR. According to cluster analysis carried out separately for chemical data and biological data, we observed that those samples that have similar chemical composition do not show similar toxicity, which is probably due to different bioavailability of contaminants, the impacts of soil characteristics as well as interaction of contaminants. According to the investigation of sensitivity of the examined four biotests the following conclusion could be drawn: P. phosphoreum and A. agile tests are similar in the sense that they are sensitive to Cu to a large extent and also to PAHs and hydrocarbons (CH) to a lesser extent. B. subtilis test corresponds well with P. fluorescens test method since both tests give good correlation with heavy metals. Neither B. subtilis nor P.fluorescens biotests are sensitive to organic soil contaminants such as PAH and CH.