| With the implementation of "Environmental Protection Law of the People’s Republic of China", which was enacted on January1,2015, the pollutant total amount control is referred to a new level. So the pollutant total amount control research based on the theory of water environmental capacity has an important theoretical values and practical significances. Water environmental capacity of heavy metals was chosen as the research object. Compound toxicity of heavy metal lead (Pb) and nanomaterial (nano-TiO2) and their influence on the environmental capacity are studied in this research, the findings demonstrated that the nano-TiO2changes bioaccumulation of Pb and its toxicity. The research showed the influence of Pb on the development of thyroid gland and nervous system with and without nano-TiO2. Mathematical models were applied to analyze the difference of each index under the above two conditions, so the results of the variance analysis can be applied to traditional water environmental capacity calculation model. The research contents are as follows:choosing the zebrafish (Danio rerio) embryos which are2hours after fertilization and puting them in Pb exposure (0,5,10,20, and30μg/L) respectively and Pb, nano-TiO2(0.1mg/L) co-exposure for6days. The level of thyroid hormone (T3and T4), thyroid hormone related gene expression (tshβ、tg and TTR), nervous system related gene (a-tubulin、mbp、gfap and shha) expression and locomotor behavior index are determined. The differential data are calculated by Matlab software in combination with Logistic model to get correction parameter y, and then put forward a more scientific water environmental capacity calculation method. The main conclusions of this study are as follows:(1) Thyroid hormone (T3and T4) level decreased significantly with the Pb exposure to zebrafish for the concentration of30μg/L. But under low concentration (5μg/L), it has shown an increase of bioaccumulation, therefore, the low concentration of heavy metal enrichment phenomenon should be focused on. Genetic results also showed significant changes, tshβ gene appeared to rise, tg、TTR、a-tubulin、mbp、gfap, and shha mRNA expression levels were significantly decreased, which shows that Pb in low concentration also has the ability to interfere the endocrine and nervous system. By further study on locomotor behavior indexes, the results showed that Pb affected the kinematic behavior of zebrafish by intervening in nervous system development and reducing its movement speed in water.(2) When zebrafish was exposed to Pb and nano-TiO2, the level of thyroid hormone was decreased more compared with Pb exposure. The enrichment of Pb in fish showed more significant increase at the concentration of20μg/L. In the co-exposure group, tshβ gene expression level increased singnificantly than the single exposure of Pb whereas other genes (TTR、a-tubulin、mbp、gfap and shha) showed significant decrease. Differences in locomotor behavior came up at the concentration of5μg/L group. The experimental results showed nano-TiO2can increase the interference of Pb on thyroid and nervous system development, inducing more serious developmental defect. Results also proved that the nanomaterial has potential environmental risk as environmental pollutant carrier.(3) Based on the result difference in the toxicological experiment, the correction parameters y was calculated by Logistic model, the results are as follows:y=0.64. One function was used to verify rationality of y value, y was then used in the traditional water environmental capacity calculation model to get a corrected calculation model, and applied this model to water environmental capacity calculation of river and lake-reservoir cases, and the water environmental capacity decreased by30%with new model. |
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