The toxicity and biodegradability of eight main phenolic compounds characteristic to the oil-shale industry wastewaters: A test battery approach

The toxicity of eight phenolic compounds characteristic to the oil–shale industry wastewaters was analyzed using a battery of seven microbiotests with species representing different trophic levels (photobacteria, protozoa, crustaceans, microalgae). Altogether five monobasic phenolic compounds (phenol, p-cresol, 2,4-dimethylphenol, 2,3-dimethylphenol, 3,4-dimethylphenol) and three dibasic phenolic compounds (resorcinol, 5-methylresorcinol, and 2,5-dimethylresorcinol) were studied. Phenol, 2,4-dimethylphenol, 2,3-dimethylphenol, and 5-methylresorcinol were classified as “toxic” (lowest 50% lethal (effective) concentration L(E)C50 of the battery 1–10 mg/L). P-cresol, 3,4-dimethylphenol, resorcinol, and 2,5-dimethylresorcinol were classified as “very toxic” (lowest L(E)C50 of the battery ≤1 mg/L). The most sensitive test organisms were crustaceans and/or photobacteria. The toxicity of three different equitoxic mixtures (mixture of all eight phenols, mixture of five monobasic phenols, and mixture of three dibasic phenols) was studied using Vibrio fisheri, Daphnia magna, and Thamnocephalus platyurus. For all three test organisms the toxicities of individual phenols were proved additive. The efficiency of biotreatment on the toxicity reduction of the individual phenolic compounds (2.5 mM) as well as the equimolar mixtures of all eight phenols (1/8*2.5 mM each), five monobasic phenols (1/5*2.5 mM each), and three dibasic phenols (1/3*2.5 mM each) was studied using acclimated and nonacclimated activated sludges. In the case of both activated sludges phenol, p-cresol, resorcinol, and 5-methylresorcinol were most rapidly detoxified. Dimethylphenols and the mixtures had moderate detoxification times, while the slowest was the detoxification of 2,5-dimethylresorcinol and the mixture of resorcinols. Thus, out of eight phenolic compounds studied 2,5-dimethylresorcinol was considered most environmentally hazardous as very toxic (LC50 for crustaceans 1–5 mg/L) and slowly biodegradabable.