Study of the environmental hazard caused by the oil shale industry solid waste

The environmental hazard was studied of eight soil and solid waste samples originating from a region of Estonia heavily polluted by the oil shale indu stry. The samples were contaminated mainly with oil products (up to 7231 mg /kg) and polycyclic aromatic hydrocarbons (PAHs; up to 434 mg/kg). Concentr ations of heavy metals and water-extractable phenols were low. The toxiciti es of the aqueous extracts of solid-phase samples were evaluated by using a battery of Toxkit tests (involving crustaceans, protozoa, rotifers and alg ae). Waste rock and fresh semi-coke were classified as of "high acute toxic hazard", whereas aged semi-coke and most of the polluted soils were classi fied as of "acute toxic hazard". Analysis of the soil slurries by using the photobacterial solid-phase flash assay showed the presence of particle-bou nd toxicity in most samples. In the case of four samples out of the eight, chemical and toxicological evaluations both showed that the levels of PAHs, oil products or both exceeded their respective permitted limit values for the living zone (20 mg PAHs/kg and 500 mg oil products/kg); the toxicity te sts showed a toxic hazard. However, in the case of three samples, the chemi cal and toxicological hazard predictions differed markedly: polluted soil f rom the Erra River bank contained 2334 mg oil/kg, but did not show any wate r-extractable toxicity In contrast, spent rock and aged semi-coke that cont ained none of the pollutants in hazardous concentrations, showed adverse ef fects in toxicity tests. The environmental hazard of solid waste deposits: from the oil shale industry needs further assessment.