An Evaluation Of Heavy Metals Contamination Level And Ecological Risk In The Hyporheic Zone Of The Weihe River,China

The sediment pollution caused by different metals has attracted a great deal of attention because of the toxicity,persistence,and bio-accumulation.Overreliance on agro-based farm inputs to increase agricultural yield,release of industrial waste and lack of appropriate sewerage system inside the towns that the Weihe River passes through has resulted to an increased quantity of pollutants including heavy metals being deposited into the river.The water from the river being utilized for irrigation,drinking by human and livestock and also recreational areas,concentration have been raised on the appropriateness of the river to serve the above purpose as well as the safety of the produce that depend on the river.This study aimed at investigating whether the sediments along the Weihe River have been polluted by heavy metals.This study focuses on heavy metals in the hyporheic sediment of the Weihe River,China.Different sediment samples were collected from fourteen different sites from the river.After drying these samples,HNO₃,HF,and H₂O₂ were used to digest these samples.High temperature and high-pressure digester and electro thermal plate digestion were used during the digestion process.Cu,Cr,Ni,Zn,and Pb were assessed by an“Inductively coupled plasma mass spectrometer”manufactured by American Thermoelectric.Moreover,Fe and Mn were assessed by the“Inductively coupled plasma emission spectrometer”（Icap7400） manufactured by American Thermoelectric and Arsenic,by a two-channel atomic fluorescence photometer.Considerable deviations were detected in the concentrations and distribution of these selected heavy metals along with the sediments of the Weihe River.The concentration of these variations in heavy metals were related to the various sources that were contributing to the contamination load.Contamination levels of metals were examined by using“geo-accumulation index,enrichment factor,contamination factor and pollution load index”while the ecological risk of metals was determined by“potential ecological risk and risk index.”Risk assessment was done by Hakansan method and sediment quality guideline（SQC）method.Pearson’s correlation was used to examine the correlation between the concentrations of different metals.The pollutant accumulation of metals ranked as follows:“manganese（Mn）>chromium（Cr）>zinc（Zn）>copper（Cu）>nickel（Ni）>arsenic（As）>lead（Pb）”.The average concentration of As,Cr,Ni,Cu,Zn,Pb,and Mn was 29.16,109.98,41.47,52.37,103.47,24.44,888.29 mg/kg respectively.The average concentration of Cr,Ni,Cu,Zn,Pb in theWeihe River is higher than the value measured in the“Weihe River basin”.The geo-accumulation index identified arsenic（As）as class 1（uncontaminated to moderate contamination）,whereas Cu,Cr,Ni,Zn,Pb,and Mn were classified as class 0（uncontaminated）.Through all heavy metals,As has maximum accumulation at D3 and D14,which indicates that the sediments at these locations are moderately polluted by As and belong to class 2.Additionally,at few stations,the Igeo concentrations for the Cr,Cu,Zn,and Pb are greater than zero,which shows the minimal presence of Cr,Cu,Zn,and Pb and places in class 1“Uncontaminated to moderately contaminate.”However,the average values of Igeo for Cr,Cu,and Zn are less than zero.According to the enrichment factor,arsenic originated through anthropogenic activities,and natural sources mainly controlled Cr,Ni,Cu,Zn,and Pb.The average enrichment factor value of all the metals studied showed their enrichment in the Weihe River sediments.The contamination factor elucidated that sediments were moderately polluted by（As,Cr,Cu,Zn,Mn and Pb）,whereas Ni slightly contaminated the sediments of the Weihe River.Among all heavy metals,Ni had the lowest contamination factor value at site D7（0.227）,and As the highest value at site D3（3.07）.Average CF values for all metals were ordered as follows:As>Pb>Cr>Cu>Zn>Mn>Ni.The pollution load index（PLI）is between 0.95 and 1.35.According to the pollution load index,most of the sediment sites（PLI>1）are contaminated.However,higher PLI value indicates that As,Pb,and Cr are the main cause of sediment pollution.The D13 site has the maximum PLI（1.35）in the study area,which indicates that heavy metals moderately polluted the sediment of site D13.Also,other locations except for D1,D5,and D9,where PLI is in-between 1,and 2 might be categorized as moderately contaminated,possibly because of urban activities.Meanwhile,sites D1,D5,and D9 were less than 1,indicating no pollution.The PLI followed the order of sites D13>D14>D3>D8>D2>D10>D11>D4>D12>D6>D7>D1>D9>D5.All metals posed a low ecological risk in the study area.The overall maximum ecological risk was measured for arsenic at D3（30.71）,and the minimum risk was measured for Mn at D7（0.61）.The PER for individual metal shows that degree of metal contamination is in following sequence:As>Pb>Cu>Ni>Cr>Zn>Mn.Our study showed that the PER<40 and RI<110 for the Weihe River,which is solid evidence of low risk of these metals in the subjective area.The risk index revealed that the contribution of arsenic（53.43%）was higher than the half of total risk.The maximum risk index found at D3（51.02）,and the minimum risk index was at D12（33.76）.For the contribution of metals in potential risk index（RI）,metals As,Cr,Ni,Cu,Zn,Pb,and Mn contributed 53.43%,5.82%,7.26%13.86%2.59%14.55%and2.49%,respectively.The heavy metals concentration detected were compared with consensus-based probable effect concentration（PEC）and threshold effect concentration（TEC）values.Mean values of As,Cr,Ni,Cu and Zn exceeded the TEC;only Pb concentration is under TEC.The concentration of all studied metals when compared with PEC,exceeded.Most of the metals at different sampling sites were found in the range of TEC and PEC at which occasional toxic effects are expected.In comparison with the sediment quality guidelines（SQGs）,concentrations of all heavy metals were under the maximum permissible concentrations,and these compounds looks most likely have minimum toxic effects on the biological communities in the studied area.Many metal pairs had positive correlations（P<0.01）:As-Cu（0.092）,As-Mn（0.214）,Ni-Zn（0.361）,Cu-Zn（0.203）and Zn-Pb（0.242）.While As-Cr（0.389）displayed a significant positive correlation at P<0.05.In addition,Cr-Zn（0.008）and Ni-Pb（0.170）showed a relatively weak correlation.