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.