Water Quality Analysis And Environmental Risk Assessment Of Heavy Metal Pollution In Water And Sediments From A Crater Lake(Lake Bosumtwi/Bosomtwe)

One of the six major meteoric lakes in the world,Lake Bosumtwi,is of great ecological significance for Ghanaians and the scientific community,most importantly for tourism,agricultural and human consumption.The present study seeksto explore the hydrochemical processes,assess the suitability of water for irrigation and human consumption,evaluate the health implications of human exposure to trace metals,and to determine sedimentary pollution levels and the environmental exposure risk.Thirty samples(30)samples of water and sediments were taken for analysis.For water,the total and dissolved lead,cadmium,mercury,nickel,chromium,cobalt,and arsenic were analyzed for trace metal levels whereas,pH,electrical conductivity,temperature,turbidity,total dissolved solids,total suspended solids,color,hardness,biochemical oxygen demand,chemical oxygen demand,nitrate,sulphate,calcium,chloride,magnesium,sodium,potassium,carbonate and bicarbonate were measured for physicochemical parameters.For sediments,Fe,As,Hg,Co,Cr,Ni,Cd and Pb were measured for trace metals while,sediment grain sizes and total organic carbon(TOC)were measured for physicochemical parameters.This dissertation research was written in three data chapters;they are:1.Hydrochemistry and multivariate statistical analysis of the quality of water from a crater lake(Bosumtwi)for agricultural and human consumption:Thirty water samples(n=30)were collected and analyzed for pH,electrical conductivity(EC),temperature,turbidity,total dissolved solids(TDS),total suspended solids(TSS),color,hardness,biochemical oxygen demand(BOD),chemical oxygen demand COD,nitrate,sulphate,calcium,chloride,magnesium,sodium,and potassium.The recorded values for pH,EC,color,COD,sodium and potassium exceeded the WHO and CCME permissible limit.Water Quality Index(WQI)assessment showed that the lake water is not suitable for human consumption.Calculated results of SAR and SSP indicated that the water from the lake is not suitable for irrigation.The Piper-Trilinear diagram showed three faces that indicate that the lake's chemistry is dominated by alkalis earth and weak acids.The order to which cations dominated and influence the water quality is:Na⁺(82.22%)>K⁺(8.36%)>Mg²⁺(8.25%)>Ca⁺(1.17%).Similarly,the dominant anions were in the order HCO₃^-(79.39%)>by Cl^-(20.17%),>SO₄^-(0.38)>NO₃^-(0.06).The Gibbs ratio revealed that the exchanges between rock and water control lake Bosumtwi's water chemistry.From the USSL diagram,all the thirty water samples fell under high salinity hazard and high sodium(alkali)hazards rendering them unsuitable for irrigation purposes.Principal component analysis(PCA)revealed that the main contributors of pollution were geogenic,domestic and agricultural runoffs,seasonal variation,unchecked application of fertilizers and agrochemicals.Five statistically significant clusters were created as monitoring sites.The interrelationship among parameters was established by the moderate to strongly negative and positive Pearson's correlation among parameters.The findings will provide a reference for policymakers and decision-makers at Lake Bosumtwi.2.Cancer and Non-Cancer Risks in Humans Exposed to Trace Elements in Drinking Water from a Crater Lake(Bosumtwi):The total and dissolved heavy concentrations of Pb,Hg,Cd,Ni,Co,Cr,and Asin water samples from the Lake Bosumtwi were determined.The results showed that the mean concentrations for dissolved Cr,Ni,and Co were below detection limits.The order of concentrations of dissolved metal reported in the present study at Lake Bosumtwi was As>Pb>Hg>Cd.Whereas for the total metal concentrations,As>Pb>Cd>Hg>Cr has been ordered for the metal levels in the Lake.Total As(0.198 mg/L),Pb(0.053 mg/L),Hg(0.014 mg/L)and Cd(0.018 mg/L)levels were higher than the WHO guideline values of 0.01mg/L,0.01mg/L,0.001mg/L and 0.003mg/L for safe drinking water.As the metal concentrations of Cr(0.0032 mg/L)were within the WHO threshold set for Cr(0.05 mg/L).The HQ values for child and adult oral(except adult exposure to As)and dermal exposure to both dissolved metals and total metals from the Lake Bosumtwi were less than one.HQ value of 1.48 was recorded for adult oral exposure to total As from the Lake indicating a potential health effect.Additionally,for child and adult exposure to total heavy metals the hazard index value of 0.73 and 1.53 were reported respectively.Arsenic contributed 96.39%and97.29%respectively to child and adult non-carcinogenic risk.The cancer risk estimations were below the range of cancer values set by USEPA.From the PCA and cluster analysis,As,Pb,Cd and Hg were of anthropogenic origin,whereas Cr was of natural origin.3.Spatial Distribution and Eco-Environmental Risk Assessment of Heavy Metals in Surface Sediments from a Crater Lake(Bosumtwi):Herein,the concentrations of Fe,As,Hg,Ni,Cr,Co,Pb and Cd were analyzed in 30sediment samples from the Bosumtwi Lake.Cd and Pb were below detection limits,while mean concentrations of As,Hg,Ni,Cr and Co showed no harmful biological effect as their levels were below their corresponding Threshold Effect Level(TEL)and Probable Effect Level(PEL values.Pollution indices such as enrichment factor(EF),contamination factor(CF),geoaccumulation(I_geo)and pollution load index(PLI)were used to estimate Sedimentary pollution levels,and the environmental exposure risk was calculated using Hakanson's ecological risk indices(PER).The results from PER estimation showed that the sediment of Bosumtwi Lake is at moderate environmental risk.From the results of EF,Hg was the major contributor to PER with a risk contribution of 96.95%.In this regard,Hg flux needs to be controlled in order to conserve the ecology of the lake.Correlation,principal component and cluster analysis revealed that main sources of Hg were agrochemicals and atmospheric deposition,while the sources of Fe,As,Co,Cr and Ni to Bosumtwi Lake were natural processes and lithology.There was no strong significant correlation between heavy metals,sediment grain sizes and total organic carbon(TOC)indicating their lack of control in heavy metal distribution,source and pathway of transport.Therefore,human health risk assessment of trace elements from the consumption of fish and local crops from the lake's catchment area is highly recommended for future studies.Authorities must set up a lake management system to safeguard the ecosystem.Local people's capacities must be built,including awareness on the consequences of the use of inorganic fertilizers and pesticides.Ultimately,there should be enough waste collection bins and toilette facilities around the lake area for visitors to use.Finally,With the population increases in the lake's catchment area,the risk of a significant increase in heavy metal loadings in sediments is possible.Effective management and sustainability measures must therefore be taken to protect Lake Bosumtwi and a comprehensive study on Hg bioavailability in Bosumtwi lake sediment is highly recommended.