Toxicity of neutralized wastes following a synthesis of chlorinated hydrocarbons to Daphnia magna and Chlorella sp.

Abstract

The present study was undertaken to compare the usefulness of animal and plant bioindicators for evaluation of a new method of effluent neutralization following; a synthesis of chlorinated hydrocarbons: chloromethans (CM) and vinyl chloride (VC). The effluents were neutralized with aqueous solution of NaOH and catalysts: iron and NG-87 (triethylbenzammonium chloride) at a temperature of 110°C. Two products were. obtained: a sediment and filtrates as a sewage. To estimate the sewage toxicity before and after the neutralization process biological and chemical tests were applied. Crustacean Daphnia magna (test response: lethality — LC₅₀) and alga Chlorella sp. (growth of biomass or chlorophyll content — EC₅₀). were used as test organisms. Oxidizability (potassium permanganate value) was applied as a chemical test. The neutralization process in both cases (CM and VC) decreased the oxidizability by 100-fold. However, 24-h LC₅₀) values (D. magna) computed for CM and VC neutralization processes decreased 680 and 6 times, respectively. Differences were even greater, when Chlorella sp. was used. Seventy-two-hour EC₅₀ values of neutralized wastes were 1510 and 4 times greater then EC₅₀ for crude sewage of CM and VC, respectively. It is worth noticing that the same trends of decreasing toxicity were obtained for both bioindicators. The precipitates were not toxic to either bioindicator when extracted in water. Both test organisms are convenient for evaluation of industrial effluents and sewage treatment. However, D. magna is much more sensitive to chlorinated hydrocarbons than Chlorella sp.