| Trace metals and metal-containing nanoparticles(NPs)are widely present in surface water and groundwater.The application of nano-products and processes of industry and agriculture have accelerated the increase of trace meatals and metal-NPs in water environment.Furthermore,they were accumulating and releasing in pipelines during the transportation of source water to users after water treatment.Some metals are persistent,carcinogenic,bioaccumulating and amplifying.NPs can act as carriers of other pollutants and be toxic to some extent,therefore,it has potential environmental risk.Accordingly,in this study,some regions were selected,which are located under the jurisdiction of 32 provinces,municipalities,autonomous regions and special administrative regions.281 terminal tap waters were taken as the research object.Trace metals and metal-NPs were analyzed by single particle inductively coupled plasma mass spectrometry(SP-ICP-MS)technology in tap water.Their spatial distribution characteristics and influencing factors were revealed,which will provide a basis for the reasonable formulation of relevant water quality index and the control of water quality standard exceeding.The metal pollution level was different in different regions.These places held a high level of pollution,which located in Anhui Province,Shandong Province,Yunnan Province,Heilongjiang Province.Some typical metals,for example,the content of Al was ranging from nd to 422.89μg/L,with 11 samples exceeding the standard.Cr was in the range of 0.02–41.10μg/L.Mn was found that one sample exceeded standard,at the concentrations ranging from 0.02 to 232.58μg/L.Fe was discovered at the concentrations ranging from 0.14μg/L to1189.00μg/L,with 2 samples exceeding the standard.The variation range of Ni was from nd to 26.77μg/L,with one sample exceeding the standard.There is a sample exceeding the standard for Zn,with the concentrations ranging from 0.001μg/L to 1066.96μg/L.The level of As was ranging from 0.02μg/L to 12.10μg/L,with one exceeding standard sample point;The variation range of Pb was from nd to 5.08μg/L.The average metal concentrations in tap water in China according the following order:Sr(294.81μg/L)>Al(59.48μg/L)>Zn(57.10μg/L)>Fe(31.51μg/L)>Cu(5.51μg/L)>Mn(4.02μg/L)>V(1.28μg/L)>As(1.16μg/L)>Ni(1.10μg/L)>Se(0.80μg/L)>Cr(0.79μg/L)>Ti(0.24μg/L)>Pb(0.21μg/L)>Cd(0.01μg/L)>Ag(0.003μg/L).Al and Fe were the main pollution elements in the research scope.Except As,the evaluated metals in tap water had no significant non-carcinogenic risk for adults and children,but the carcinogenic risk of metals was high.The carcinogenic level had the followed order:As>Cr>Cd>Pb.As was the main contributor to the total carcinogenic risk,and Pb didn’t have carcinogenic risk.In addition,children were more sensitive and vulnerable to trace metals in tap water.The particle concentrations of different metal-NPs in tap water varied greatly.The concentration of Fe-NPs was high and widespread,with obvious regional characteristics,ranging from 4.74×10~6particles/m L to 3.72×10~9 particles/m L.In general,the concentration of Fe-NPs in the south was higher than that in the north.The concentration of Pb-NPs was low,with high spatial heterogeneity,ranging from nd to1.36×10~7 particles/m L.Moreover,Pb was mostly wrapped around Fe-NPs.The content of Ti-NPs was stable in different regions,with the range of nd to 1.44×10~7 particles/m L.In this study,environmental factors such as trace metals,dissolved organic carbon(DOC),sulfate,nitrate(calculated by N),salinity,and water sources,faucet materials,pipeline materials,floors,natural conditions,social and economic data were considered to reveal influencing factors of typical trace metals and metal-NPs in tap water based on machine learning by lasso regression and bayesian network method.Trace metals in tap water are mainly affected by source water and pipelines,including industrial processes,atmospheric deposition and mining,which will affect the background value of metals in source water.The water distribution system,pipes and taps et al.will lead to the deposition and release of trace metals.Water environment conditions such as p H and sulfate can also promote the deposition and leaching of metals.In addition,they were also affected by the treatment process of waterworks,such as the addition of different coagulants and final disinfection.Furthermore,multiple metals are homologous and interdependent,and a variety of metals are also influenced by nanoparticles adsorption.Different metal-NPs were affected differently by their corresponding total metals in tap water.Among them,the particle concentrations of Ti-NPs and Pb-NPs were greatly affected by total Ti and total Pb,but Fe-NPs was less affected by total Fe.In addition,NPs was also received by the combination of other metals.Ti-NPs and Fe-NPs may be affected by the addition of titanium salt and ferric coagulants in water treatment plants.Fe-NPs are also affected by metal pipelines and source water(surface water).Besides,different pipeline materials,engineering nanomaterials,which could enter the tap water distribution network,also affected the release of metal-NPs. |
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