Petroleum products are complex mixture of compounds of varied biological properties. They can

cause harmful changes in contaminated ecosystems and threaten humans and living organisms as well. Bioremediation (including bioremediation stimulated by biogenic substances and inoculation with biopreparations

from autochthonous bacteria and fungi) can result in creation of metabolites of a varied structure and biological

activeness, which has been partly recognised. Some of them are more toxic than an initial substrate. Besides,

they might have mutagenic features and be responsible for cancer. Estimation of bioremediation effectiveness in

waste pits was completed with toxicological monitoring. It was led with the use of living organisms as biomarkers representing all trophic levels of a chosen ecosystem: producers, consumers and reducers. This process enables total estimation of natural environment conditions. The aim of the research was to determine the influence

of petroleum contaminants and indirect metabolites (produced during bioremediation) on soil biocenose. The

results of biotests (toxicity, phytotoxicity and genotoxity) have been taken into account. The following biotests,

prepared and produced by Microbiotest, have been applied: PhytotoxkitTM, Ostracodtoxkit FTM, acute toxicity

tests Microtox® Solid Phase and Ames mutagenicity tests. The obtained results enabled observation of changes

in toxic properties during purification of the soil taken from waste pits. In addition, it can be claimed whether

the areas are suitable for forest usage.

Operations conducted by petroleum industry generate an entire range of drilling waste. The chemical composition of drilling waste and its toxicity depend primarily on the geological and technological conditions of drilling, the type of drilled rock deposits and on the type and composition of the drilling mud used. In the course of drilling operations, drilling fluids are in constant contact with bacteria, fungi and other organisms infecting the mud. Pioneer species, capable of surviving and using the resources of this specific environment, are selected. For this reason, the effectiveness of microbiota survival on different types of spent drilling muds and in different dilutions with brown soil was measured. Spent drilling muds samples came from drilling operations in various regions of Poland, e.g. Subcarpathia, the Polish Lowland and Pomerania regions. Oxygen consumption after 96 h was around 20 μg·g^‒1 dry mass in soil or soil/drilling water-based mud mixture. Soil mixes contained 10 wt% synthetic base, mud had a higher oxygen consumption – 38 μg · g^‒1 dry mass. Oxygen consumption decreases sharply as the content of the spent synthetic base mud fraction increases. A higher concentration of spent SBM (35 wt%) reduced the aerobic metabolism by slightly more than 50%. A high concentration of reduced carbon decreased the respiratory quotient (RQ) value to 0.7. All the researched drilling waste shows microbiological activity. At the full concentration of drilling fluids and non-dilution options, the chemical composition (salinity, inhibitors, etc.) strongly inhibits microbiota development and consequently, respiration