HUMAN HEALTH RISKS ASSOCIATED WITH HEAVY METAL-CONTAMINATED SOIL AND FOOD PLANTS IRRIGATED WITH WASTEWATER

Abstract

Long-term wastewater irrigation is not only a way of contaminations of soil with heavy metals (HMs) but also accumulates HMs in food crops. Samples of both soil and vegetables were collected from wastewater irrigated sites of Peshawar, Pakistan in winter and summer seasons for analysis of HMs concentrations in them and to investigate the health risk of associated with HMs contaminated vegetable. The mean concentrations (mg/kg dry weight) of selected HMs like Cu, Pb, Cd, Ni, Zn, Mn, Cu, Co and Hg in soil irrigated with wastewater in winter, summer seasons and preference soil were 56.9, 37.01 and 13, 61.28, 62.1 and 10.4, 7.68, 8.9 and 1.2, 100.78, 106.64 and 23, 159.55, 193.4 and 12, 341.33, 387.7 and 14, 40.54, 41.1 and 24, 61.64, 88.2 and 15 and 459.455, 93.1 and 23 mg/kg, respectively Similarly the mean concentrations (mg/kg dry weight) of studied HMs like Cu, Pb, Cd, Ni, Zn, Co, Cr, Hg, Mn and Fe in the vegetables grown in wastewater irrigated soil in winter, summer season and preference soil were 26.8, 24.69 and 13 63.7, 44.7 and 11.45, 8.3, 13.98 and 3, 38.31, 34.and 32.4, 64.1.128.1, and 33, 25, 21.77 and 11, 20.7, 57.45 and 31.68, 421.76, 497.55 and 100.01, 41.1, 32.26 and 17 and 576.85, 632.3 and 300 respectively. The concentrations of studied HMs were significantly higher in both soil and vegetables samples collected in summer season than their concentrations in winter’s samples. The concentrations of Pb, Cd, Ni and Cr exceeded their respective permissible limits set by WHO/FAO. Transfer factor (TF) values of selected HMs from soil to vegetables and the target hazard quotients (THQs) to the possible health risks to local population through the food chain were also calculated. The mean values of root transfer factor (RCFs) ranged from 0.3-1.4, 0.2-1.4, 0.4-3.7, 0.4-1.1, 0.3-0.6, 0.004-0.18, 1-1.8, 0.12-1.5 and 0.4-1.08 for Pb, Cu, Cd, Ni, Zn, Mn, Co, Cr and Hg, respectively in vegetables of study area.. Similarly, values of shoot transfer (SCFs) for Pb, Cu, Cd, Ni, Zn, Mn, Co, Cr and Hg ranged from 0.2-1.4, 0.2-4, 0.3-4.7, 0.2-0.8, 0.47-2.46, 0.02-0.45, 0-1.2, 0.34-2.2 and 0.5- 2.01, respectively in the samples of vegetables. Values of fruit transfer (FCFs) were 0.3- 1.1, 0.2-2.4, 0.8-5.7, 0.2-0.6, 0.31-0.69, 0.002-0.14, 0.4-1.6, 0.3-1.4 and 0.6-0.8 for Pb, Cu, Cd, Ni, Zn, Mn, Co, Cr and Hg, respectively. The dietary intake of metals (DIM) values of Pb, Cd, Ni, Zn, Mn, Cr and Cu by children were ranged from 0.001-0.019, 0.001-0.005, 0.01-0.02, 0.013-0.038, 0.01-0.02, 0.003-0.018, 0.001-0.011, respectively. Similarly the values of DIM for Pb, Cd, Ni, Zn, Mn, Cr and Cu by adults via consumption of vegetables were 0.01-0.023, 0.002-0.006, 0.001-0.03, 0.014-0.042, 0- 0.13, 0.002-0.032 and 0.001-0.013, respectively. The DIM values of Pb and Cd were significantly (p<0.05) higher as compared to respective reference dose (RfD). However, the DIM values of Zn, Cu and Mn were significantly (p<0.05) lower than their respective RfD. The THQ of Pb, Cd, Ni, Zn, Mn, Cr and Cu ranged from 0.668-5.055, 1.362-5.609, 0.36-1.23, 0.044-0.126, 0.08-3.46, 0.002-0.019 and 0.025-0.281, respectively for children. Similarly, the THQ ranged from 0.744-5.586, 1.517-6.248, 0.049-0.119, 0.12- 3.86, 0.002-0.021 and 0.028-0.313 due to Pb, Cd, Ni, Zn, Mn, Cr and Cu, respectively for adults. Greenhouse pot experiments using spinach (Spinacia oleracea) coriander (Coriandrum saivum), purslane (Portulaca oleracea) as representative vegetables were conducted to assess the up take pattern of three different doses of Cd, Pb, Zn, Cd/Pb, Cd/Zn and Pb/Zn The highest dose of Cd, Pb and Zn in single form and in mixture (Cd/Pb, Cd/Zn and Pb/Zn) significantly reduced the growth S. oleracea, C. saivum and P. oleracea seedlings. Similarly, in case of full grown plants of S. oleracea and C. saivum the highest doses of Cd, Pb, Zn, Cd/Pb, Cd/Zn and Pb/Zn reduced the growth In case of all S. oleracea, C. saivum and P. oleracea seedlings the concentrations of Cd, Pb and Zn were positively correlated with their concentrations in soil. The mixture of HMs such as Cd/Pb, Cd/Zn and Pb/Zn the metals behaved antagonistically, which were reflected in the growth parameters of selected plants. In case of full grown plants of S. oleracea and C. saivum the Cd, Pb and Zn concentrations in soil and roots of plants were positively correlated. Similarly, the concentrations of Cd, Pb and Zn in the root and shoot of full grown plants of S. oleracea and C. saivum were positively correlated. Total protein content, fiber and moisture contents of S. oleracea, C. saivum significantly reduced with increasing concentrations of Cd, Pb and Zn alone and also their mixture (Cd/Pb, Cd/Zn and Pb/Zn) in plant tissue. The impacts of mixture of Cd, Pb and Zn on total protein, fiber and moisture content were more sever than the impacts of individual Cd, Pb and Zn but less than the sum of impacts of individual HMs. Similarly, the increasing concentrations of selected HMs reduced the up take of Na, K, Ca, Fe, Mg, Mn and Cu by S. oleracea and C. saivum. It was concluded from this study that soils of Peshawar are rich with HMs because of wastewater irrigation. The plants grown in these soils contaminated with HMs. The HMs adversely impacted the growth parameters of plants, change the up take of important metals by plants and reduced moisture contents, total protein and fiber. The consumption of vegetables in the wastewater irrigated areas in a Peshawar causes health risks to the residents.