Research On Environmental Behavior And Health Risks Of Heavy Metals And Organochlorine Pesticides In Qingshui River

Heavy metals(HMs)and organochlorine pesticides(Organochlorine Pesticides,OCPs)are two typical persistent toxic pollutants.They can migrate and transform among the overlying water,interstitial water,and sediment by various physicochemical and biological processes in river system,bringing irretrievable damages on the river water.Therefore,it is of great significance to delineate the environmental behavior,partitioning mechanisms,and health risks of HMs and OCPs river water system.This study took Qingshui River as an an example to study the speciation,historical settlement records,main sources,potential ecological risks,human health risks,and environmental geochemical behaviors of HMs and OCPs in water and sediment samples.Various methods including multivariate statistical analysis,isotope dating and mathematical models had been adopted.The factors controlling the fate of HMs and OCPs as well as adsorption model were also studied.The main results were summarized as follows:(1)A systematic study of the occurrence,source,fate and ecological risks of HMs and OCPs in sediments found that the enrichment ratio,geo-accumulation index,and potential ecological risks of HMs in the sediments of the Qingshui River Basin all decreased with the increase of depth.The ecological risks of Cd and Hg was higher than other metals,and their biotoxicity effects may occur frequently in some sections of the river.The heavy metal pollution mainly came from human activities.A total of 19 kinds of OCPs were detected in the sediments,with the detection limit varying from n.d.to 36.527 ng · g-1,and the detection rate was 79.05%.The OCPs in sediments were mainly DDTs and Endosulfan.The content of OCPs in the entire watershed generally showed an increasing trend with the increase of depth,peaking in the deposition range of 15?20 cm.Endosulfan in OCPs had certain potential ecological risks,especially in the deposition range of 5?10cm,which may cause potential harm to biological organisms.Pollution generated by the four typical organochlorine pesticides(such as HCHs,DDTs,Endosulfan,and Chlordane)mainly came from historical residues,but a small amount of lindane,dicofol,endosulfan and chlordane compounds had been input into the local environment in recent years.(2)Using the 210Pb isotope dating method,the sedimentation records of HMs and OCPs were studied to reveal the sedimentation records of HMs and OCPs from 1977 to 2017.Heavy metal pollution was related to economic development,whereas OCPs pollution was found to be related to usage of pesticides.During the period from 1977 to 2017,the degree of HMs pollution in sediments continued to increase over time,while the pollution degree OCPs basically continued to weaken.Heavy metals and OCPs significantly polluted the river during 1993-2001 and 1985-1993 respectively.(3)The study revealed the relationship and interaction mechanism between pollutants(OCPs and HMs)and physicochemical parameters and nutrient elements in the sediments.A functional model between HMs,OCPs adsorption and control factors was preferably established.The study found that Cd and Hg,As and Pb in the sediments of Qingshui River had similar sources and distributions,whereas the enrichment of Cr was distinct from these toxic metals.Among them,TOC and salinity in the surface sediments had a certain influence on the accumulation and migration of Cd and Pb.The study also found that Cd and TOC have affinity,and the increase of Pb release increased gradually with the increase of salinity gradient,and surface sediments in high salinity environments had greater adsorption efficiency for DDTs.The content of ?-HCH and HCHs decreases with the increase of pH.TN and TP had a certain influence on the enrichment of Endosulfan II and DDT in the sediments.In the sediment,Cr and Pb,Cd,As,and Pb had certain effects on the accumulation and enrichment of Endosulfan,p,p'-DDT,Heptachlor epoxide and DDE,p,p'-DDE and DDE,respectively.(4)Using sampling questionnaire surveys and actual measurement methods,the basic,drinking water,and the skin exposure parameters of more than 1,600 residents around the basin were studied.It found that the drinking water intake rate,wading behavior frequency and duration of the population greatly varied,which were affected by factors,such as urban and rural areas,gender,age,and seasons.The specific surface area of the skin was also affected by factors,such as age,urban and rural areas,and gender.(5)The research on the potential health risks caused by different exposure pathways of water weight metals and OCPs to different groups of people found that the total health risks of heavy metals and OCPs in water bodies to different groups of people varied from 1.575×10-5 to 1.640×10-4 a-1,and followed the decreasing time order of the dry season>spring flood season>summer flood season.The health risk of drinking water exposure was higher than that of skin exposure.Male health risks were higher than females,and the younger the male people,the greater their health risks.Women had relatively higher skin exposure health risks than man,especially those from urban area in the age of 18?40 years old.Hand suffered the highest health risks through skin contact among the human organisms.Adult women were significantly higher than the other groups.Carcinogenic HMs in the water environment were the key factors to control,especially.As that should arise special attention in the dry season.The above research results provided a scientific basis for controlling the pollution of HMs and OCPs in the Qingshui River and for effective environmental risk management.This study also has important guiding significance for the governance and improvement of the water environment of the basin.