Distribution, Correlation, Multivariate Apportionment and Risk Assessment of Selected Metals in Water, Soil, Sediments and Fish as a Measure of Pollution Index in Freshwater Reservoirs

Abstract

Water quality of freshwater reservoirs in Pakistan is degrading because of excessive anthropogenic pollutant inflows. There is a dire need for appropriate environmental monitoring and evaluation of related health risks for future planning and management of these resources. The present study was carried out in order to evaluate the distribution, correlation, source apportionment, health/ecological risk assessment and seasonal variations of selected metals (Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Pb, Sr and Zn) in water, related soil, top sediments and selected fish species from the freshwater reservoirs (Rawal Lake, Khanpur Lake and Simly Lake) around Islamabad, Pakistan. The metal contents in water and soil were also assessed from a background/remote area for comparative evaluation. In addition, some physicochemical parameters (pH, T, DO, TA, EC, TDS, TH, Cl-, HCO3-, RSBC, SAR, PS, KR, Mg/Ca, MAR, PI) were estimated in the water and soil/sediment samples. Measurement of the metal concentrations in each sample was carried out by atomic absorption spectrometry following the standard methodology. Multivariate methods were used to identify the pollution sources, while non-carcinogenic health risk assessment was computed to determine the adverse health effects (via oral route and dermal contact) on the population. Pollution indices of the metals in soil and sediments were assessed by calculating their geoaccumulation index, enrichment factor, contamination factor, degree of contamination, potential ecological risk factor and potential ecological risk index. In water samples from background area, average metal levels exhibited following decreasing concentration order: Ca > Na > Mg > K > Pb > Co > Cu > Zn > Mn > Cr > Fe > Cd > Li, hence, Ca, Na, Mg and K emerged as dominant contributors. Investigation of the water quality from Rawal Lake manifested that measured levels Cd and Pb were higher than the permissible limits, whereas, DO contents were lower than the desired levels. The hazard quotients of Cd and Pb were found to be higher than the safe limits, posing threat to the consumers. Average levels of Cd, Co, Cr and Pb in the water samples from Khanpur Lake and Simly Lake were significantly higher than the permissible levels, suggesting potential adverse health effects to the consumers, also manifested by the hazard quotients of the metals. Nevertheless, no risk was associated with the selected metals due to dermal contact. Multivariate PCA and CA revealed significant anthropogenic contributions of some metals in the water samples from each reservoir. The soil samples were analyzed for water soluble and acid extractable fractions of the selected metals. Among the metals, Ca, Na, K, Mg, Fe and Pb were estimated at relatively higher levels in the water-extract of soil from background area, while, in case of acid-extracts, Ca, K, Fe, Mg, Mn and Na were found at elevated concentrations. The correlation study revealed appreciably diverse mutual relationships of the metals in the soil samples, while, PCA and CA exhibited divergent apportionment of the metals in soil samples. Significant to extreme anthropogenic enrichment of Cd, Pb, Li, Zn, Cr, Cu, Mn and Co was observed in the soil samples. In water-extract of the soil samples around the Lakes, relatively higher levels were noted for Na, Ca, K, Fe and Mg, while, in acidextract of the soils, Ca, Fe, Mg, Na, K, Mn and Sr were the dominant contributors. Most of the metals showed random distribution with diverse correlations during summer and winter. PCA and CA revealed significant anthropogenic intrusions of Cd, Pb, Co, Cr, Cu, Li and Zn in the soil samples. Geoaccumulation indices and contamination factors indicated moderate to heavy contamination for Pb and Cd in the soils, while enrichment factor exhibited significant enrichment (EF > 5) of Cd, Pb, Co, Mn, Cr, Cu, Li, Sr and Zn xxix by anthropogenic activities. Overall, on the average basis, considerable degree of contamination (Cdeg > 16) was observed in both seasons. Top sediments were collected as composite samples from each water reservoir and then oven dried, grounded, homogenized and processed to assess the water soluble and acid extractable concentrations of the metals. Physicochemical parameters were also measured in the water-extract of the sediments. Sediment quality guidelines (SQGs) and potential acute toxicity were used to evaluate the ecotoxicological effects of the metals. Relatively higher concentrations were noted for Ca, Fe, Mg, Na, K, Mn and Sr in the sediment samples. PCA and CA revealed anthropogenic contributions of Cd, Pb, Cr, Mn, Co and Li in the sediments. Enrichment factors of the metals in sediments showed severe to moderate enrichment of Cd, Pb, Co, Zn, Li, Mn and Sr. Geoaccumulation indices and contamination factors evidenced significant contamination by Cd and Pb, although on the whole, moderate to considerable degree of contamination was observed. Some of the metals levels exceeded the sediment quality guidelines, which revealed frequently adverse biological effects to the dwelling biota in the aquatic ecosystem. The sediments were found to be significantly contaminated by Cd, Pb, Cr, Mn, Cu and Zn.