| With the continuous indiscriminate use of chemicals and the random discharge of various chemical pollutants,water pollution has become increasingly serious.So the urban landscape water pollution is serious.Therefore,it is necessary and important to carry out the integrated water quality safety evaluation.In this paper,the bio-toxicity of various water bodies in Tianjin was tested based on the different trophic levels bio-toxicity test.The water quality safety of different water bodies was evaluated by TU method,water quality safety grading evaluation and ecological risk evaluation based on SSD curve,in order to provide fundmental results for the water environment protection and comprehensive evaluation of water quality indicators.In different trophic level bioassay test methods,Chlorella vulgaris,Daphnia magna and Photobacterium were used to represent the producers,consumers and disintegrator respectively.The growth inhibition experiment of Chlorella vulgaris and the lethal experiment of Daphnia magna were optimized by well plate method,which could improve the efficiency of the experiment and reduce the use of toxic substances.The EC50 values of Hg2+,Zn2+ and phenol to Chlorella vulgaris were 1.10,2.25 and 240.70 mg/L.The LC50 values of Hg2+,Zn2+ and phenol to Daphnia magna were 0.023,0.62 and 9.98 mg/L.The EC50 values of Hg2+,Zn2+ and phenol on the inhibition of Photobacterium were 0.028,0.19 and 38.30 mg/L,respectively.Water samples from an Ecological Wetland Park,an Artificial Ecological Wetland Project,a Reclaimed Water Plant,Jin River and Duliujian River in Tianjin were collected and tested for the bio-toxicity at different trophic levels.The calculated results of EQCPhenol were 0-22.66,0-11.34 and 0-23.50 mg/L,respectively.The calculated results of EQCHg2+ were 0-103.39,0-26.01 and 0-17 ?g/L,respectively.The submerge wetland treatment process of Ecological Wetland Park and Artificial Ecological Wetland Project,and the RO treatment process of Reclamed Water Plant had the best purification effect.The bio-toxicity of Jin River from upstream to downstream J1-J4 was low and the change was little.The bio-toxicity of the Duliujian River from the upstream to the downstream points L1-L5 show a trend of increasing and the bio-toxicity was high.Complex replenishment sources of Duliujian River accounted for the increase of the bio-toxicity.The water quality safety evaluation of each water sample was carried out by the TU method,the water quality safety grading evaluation and the ecological risk assessment based on different trophic level biological toxicity tests,and compare the evaluation results of each method.TU value of the evaluation results showed that the average TU values of the sample points were less than 0.4,belonging to class I,non-toxic.Compared with EQCHg2+,change gradient of water quality was more obvious.The results of evaluation based on EQCPhenol: Z4,Z5,J1 and J2 were Class A;S3-S5,K3-K4,Z1-Z3,J3-J4 and L1 were Class B;S1-S2,K1-K2 and L2-L5 were Class C.Ecological risk assessment based on phenol SSD curve showed that the ecological risk of S1 was 14.47%,the ecological risk of effluent S5 was 2.46% and lower than HC5.The ecological risk of influent K1 was 30.77%,the ecological risk of effluent K4 was reduced to 5.49% and close to HC5.The ecological risk of Z1 was 2.09% and the ecological risk of Z5 droped to zero.The comprehensive ecological risk of J1-J4 were 0.58%,0.87%,0.99% and 1.12%,which were lower than HC5.The integrated ecological risk of L1-L5 were 8.11%,13.80%,13.05%,15.06% and 29.94% and there was a growing trend.In addition,there was a good correlation between the ecological risk assessment results and the safety grading evaluation grades.The ecological risk between 10%-35% and the corresponding safety level was C;the ecological risk between 0.9%-10%,and the corresponding safety level was B;ecological risk between 0-0.9%,the corresponding safety level was A.Values of DOC and UV254 were correlated with the results of ecological risk evaluation and safety grading evaluation of water quality.The correlation of UV254 was better,indicating that macromolecular organic compounds and aromatic compounds accounted for to the increase of water toxicity.In general,toxicity of the same sample point on different test organisms had different results.The test method based on different trophic level can explore the potential risks in the process of ecological protection,and evaluate water quality safety comprehensively.Among the three water quality evaluation methods,water quality safety grading evaluation method based on EQCPhenol and ecological risk assessment method based on phenol SSD curve were better,and the two evaluation methods had a good correlation.The results can be used to characterize the water quality toxicity of various water bodies in Tianjin. |
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