Water Safety Evaluation Based On Biological Toxicity Test Method And Its Application

The safe water quality has important impacts on not only the health of ecological system, but also the survival and development of human beings. With the intensification of human activities in recent years, an increasing number of chemical pollutants enter the environment, either directly or indirectly, causing serious water pollution. Due to a wide range of pollutants discharged into the aquatic environment, while each pollutant often have a variety of biological effects, so the conventional safety assessment methods based on the water quality criteria are not reliable enough. The toxicity tests can vividly reflect the whole adverse biological effects of multiple chemicals in water body, which has been regarded as a beneficial supplement for conventional water quality assessment methods based on physicochemical parameters.Based on biological effects of contaminants, the common biological toxicity testing methods were summarized; both characterization methods for toxicity of water samples and water safety evaluation method based on biological toxicity tests were discussed. The advantages and disadvantages of each method were described, and the progress in this area was reviewed as well.To evaluate a variety of biological effects of contaminants in environmental water samples, two acute toxicity testing methods (Daphnia acute toxicity, Luminescent bacteria toxicity test) and two special toxicity test methods (endocrine disrupting toxicity, genetic toxicity) were optimized. After ensuring the accuracy of toxicity testing, sample volume, number of test organisms, exposure concentration and test equipment, etc. were optimized. For example, the luminescent bacteria toxicity test method was changed from the traditional method to96-well plates, which not only reduces the volume of the exposure solution, but also shortens the test time; Daphnia acute toxicity tests based on the traditional method, used24-well plates as exposure container, which can reduce the volume of exposure solution, at the same time, the burden on field sampling was reduced by reducing the amount of the sample; For yeast two-hybrid experiments, the concentration gradient of toxicity tests and the description method for the results of toxicity tests were determined, meanwhile, preparation of the solution and the experimental procedure was optimized, the purpose of rapid and efficient detection was achieved. Based on toxicity test battery, a new water safety assessment method was established, namely water safety classification method.Finally, by using optimized biological toxicity test methods and the newly established evaluation method for water quality safety, toxicity of water samples collected from wastewater treatment plant of a pharmaceutical factory in Wuxi city and reclaimed water samples from a park in Beijing City were evaluated. It was found that the toxicity of water samples from pharmaceutical factory mainly exhibited as genotoxicity and acute toxicity, while endocrine disrupting effects of all water samples were very weak. Overall, toxicity effects of the influent were most significant, and the toxicity score of acute toxicity and genotoxicity reached3, the toxicity rank of influent was C-level, which belonged to poor water quality. After anaerobic treatment, MBR treatment, especially nanofiltration treatment, toxicity ranks of water quality raised from the original C-level to B-level, and then raised to A-level. But the water quality of nanofiltration concentration solution was still at B-level. In addition, the toxicity rank for effluent gradually increased from B-level to A-level after the anaerobic treatment and the oxidation pond treatment, settling ponds treatment, concentrated water treatment, the water quality was improved correspondingly. The water quality of effluent sample had not been significantly improved after anaerobic treatment and hydrolysis tank treatment, which still was ranked as B-level. It can be seen that, the anaerobic treatment for wastewater from pharmaceutical factory is not effective, while the oxidation pond treatment, especially nanofiltration treatment for removing organic intermediates, reducing toxic effects of water quality had more significant effect. For the studied Park loop processing system, the worst water quality in the six sampling points was found at the water inlet, with toxicity rank of C-level; there would be certain risks if water at this level was directly used for landscape recreation. After the water has flowed through the cascading flower bed and artificial wetland system, its acute toxicity and genotoxicity significantly reduced and the toxicity rank of water quality raised to B-level; the toxicity rank increased to A-level after the water has been treated in mixed oxidation pond and the water quality continued to be good (A-level) in the main lake. The above analysis shows that the park ecological reclamation system can effectively eliminate acute toxicity, genetic toxicity and endocrine disrupting effects of recycled water, thus playing a role in the improvement of water quality.