Toxicity Studies of Treated Residual Wastes in Austria using Different Types of Conventional Assays and Cost-Effective Microbiotests
Abstract : The toxicity and chemical quality of 12 mechanically-biologically treated residual wastes were studied during different treatment periods. Acute and chronic bioassays were carried out with a battery of test organisms. The acute toxicity was assessed using Daphnia magna (crustacea) and Vibrio fischeri (luminescent bacteria). The chronic toxicity was tested with Selenastrum capricornutum (green algae) and Lepidium sativum (a higher plant). In an effort to integrate less expensive methods of assessing waste toxicity, 2 cost-effective new microbiotests were used in addition to conventional bioassays. These new microbiotests were the Daphtoxkit F™ with Daphnia magna for acute toxicity and the Algaltoxkit F™ with Selenastrum capricornutum for chronic toxicity. Samples were analysed for various physico-chemical parameters (pH, conductivity, O2, BOD5, COD, TOC, NH4-N, NH3, NO3-N, NO2-N, PO4-P, SO4, Cl-, F-, and Fe). Toxicity of the samples was expressed as German regulatory G-values and Toxic units (TU). The results of these studies indicate that high toxicity was observed in samples with a short treatment period. In most cases toxicity decreased significantly when the duration of treatment increased. Marked differences were observed in the sensitivity among the test species. The toxicity was found to vary between 1 and 256 G-values and 0 and 58 TU, respectively. The results showed that Daphtoxkit F™ bioassays were as sensitive as the conventional Daphnia test. When comparing the data of Algaltoxkit F™ tests to standard algal bioassays, in most cases the same G-values and similar Toxic Units were found; differences, if any, were small (less than a factor 2). With regard to toxicity-chemistry relationships, it was found that high levels of ammonia explained a part of the acute toxicity and a good relationship was noted between the toxicity and conductivity, TOC, COD and BOD5 of the most loaded samples.
This study provides evidence that mechanical-biological treatment of waste lowers the amount of organic pollutants and decreases the toxicity. This study also demonstrates the potential of cost-effective microbiotests as alternatives to expensive conventional bioassays for routine detection of acute and chronic hazard of xenobiotics in complex wastes.