SUITABILITY OF MICROBIAL BIOASSAYS FOR BO UND CONTAMINANTS

Toxicity of soil spiked with water soluble and insoluble contaminants was assessed with bacteria. Three bioassays were used with common soil bacteria. Water soluble fractions from the soils were estimated in mi crotiterplates via dehydrogenase activity of B. cereus and growth of P . putida. A new method was developed using B. cereus to include effect s of soil particles with bound contaminants. As contaminants p-nitroph enol and 2-naphthol were tested in these systems. Results indicated th at the concentration of the contaminants in the soil solution is deter mined by soil properties. Toxicity of water soluble fractions was not only a result of the toxicant's concentration but further modified by soluble components of the soils. It is not possible to assess soil pol lution from toxicity of the water soluble fraction in general, because unknown factors of the soluble soil fraction can influence toxicity g reatly. The newly developed contact bioassay with B. cereus showed cle arly higher toxicity of 2-naphthol estimated in soil suspension than d id the comparable test system with the same bacteria using water solub le fractions only. The results stress the importance of including soil particles into bioassay procedure& It was shown that also water insol uble, bound contaminants can act as toxicants, For an estimation of to xicity under conditions more relevant for the environment, the suggest ed test system can provide useful information to bioavailability of bo und contaminants.