Water Quality Evaluation And Human Health Risk Assessment Of Dagu River Groundwater Reservoir

Dagu River groundwater reservoir is one of the most important water supply resources in Qingdao. The groundwater quality is closely related to human health. However, with the influence of human activities, the water quality is becoming worse and worse. The control of groundwater pollution is firstly established in"prevention". Therefore, in this paper, in order to investigate the contamination states and its water supply risk in time, then put forward measures of controlling groundwater pollution in Dagu River water source area, the groundwater quality is evaluated accurately, on this basis, the water pollution characters are analyzed comprehensively and the pollution causes are found out, finally the human health risks are assessed quantitatively for the organophosphorus pesticides exposure in potentially contaminated Dagu River groundwater reservoir. The research draws conclusions as follows:(1) Based on the traditional fuzzy synthetic evaluation theory, a new model with high resolution is developed to overcome the limitations of traditional model in practice. In the procedures of selecting assessment indices, calculating weighted values, choosing fuzzy synthetic operator and analyzing object vectors of fuzzy synthetic evaluation, the methods of cumulative frequency, modified clustering weight, multiplication and summation operator and weighting average principle are proposed, respectively. The new model is applied to the water quality assessment of Dagu River groundwater reservoir. Compared with the method recommended by the current groundwater quality criteria (GB/T 14848-93) in China, the improved model is proved to be reliable and superior.(2) The result of groundwater quality evaluation indicates that the water quality of study area deteriorates heavily. More than 60% of the monitoring wells are close toâ…¤level quality, with levels ranging from 4.50 to 5.00. The most severely polluted region is located in the north of Xiezhuang and the neighborhood of Shaliang and Dawangtuan in the lower reaches of Dagu River. Agricultural non-point source pollution is the main reason of groundwater quality decline.(3) The most important pollutants in local groundwater are nitrate nitrogen (NO₃-N), total hardness (TH) and total dissolved solids (TDS). The contamination degree of NO₃-N is most serious. The badly-polluted area of NO₃-N is large and regional, which is consistent with the distribution of the worst groundwater quality levels (levels ranging from 4.50 to 5.00). The abuse of chemical fertilizer in agricultural activities results in the NO₃-N pollution of groundwater in wide area. The over standard region of TH and TDS has a good consistency. The area is large, but the superstandard multiple is not large. The increasing of TH in groundwater is related to livestock manure, rural domestic wastes, excessive use of nitrogenous fertilizer and overexploitation of local groundwater. The increasing of TDS is the synthetic results of multiple contaminants such as NO₃-N and TH.(4) The author chooses 9 organophosphorus pesticides (dichlorvos, chlorpyrifos, dimethoate, malathion, methamidophos, omethoate, parathion, methyl-parathion and trichlorfon) as the objects of human health risk assessment. Among the 9 organophosphorus pesticides, except that methamidophos and trichlorfon are not detected, the detection rates of the other 7 pesticides are all more than 50%. The total content of 9 organophosphorus pesticides in study area ranges from 73.26 ng/L to 118.28 ng/L. The differences in all sampling sites are little. High detection rates, but low contents are features of organophosphorus pesticides pollution in Dagu River groundwater reservoir.(5) The U.S.EPA model of human health risk assessment is used to analyse the hazards that may be caused through drinking and dermal contact for the 7 detected organophosphorus pesticides in study area. The analysis of health risk estimates indicates that the total noncarcinogenic hazard quotient of 7 organophosphorus pesticides through both dringking and dermal contact exposure pathways is 1.04E-03, which is far below 1.0(acceptable level for human body). The total cancer incidence risk of dichlorvos is 1.59E-08, which is far lower than 10-6(acceptable level for human body). Thus the current contamination concentrations of organophosphorus pesticides do not pose direct hazards to human health. As for the combined effects of all 7 organophosphorus pesticides, the dringking exposure pathway poses a significant health risk for both noncarcinogenic hazard and carcinogenic hazard. But the dermal contact exposure pathway can't be ignored. For dringking exposure pathway, the noncarcinogenic risk-ranking order is: methyl-parathion>dimethoate>dichlorvos>malathion> chlorpyrifos>omethoate>parathion. For dermal contact exposure pathway, the risk contribution of chlorpyrifos is greatest, and its percent is 83.94%. According to the limitations of systematic methodology and available data and so on, the health risk assessment result includes uncertainty inevitably.(6) The pollution of Dagu River groundwater reservoir is mainly caused by agricultural production and rural domestic pollution sources. Therefore, in order to conserve and preserve groundwater, the local government should carry out technologies of scientific and rational use of chemical fertilizer and pesticides, straw returning and water-saving irrigation etc.in agricultural production, at the same time, strengthen rural waste utilization and management. Through the above measures, the agricultural and rural ecological environment can step into a virtuous cycle.