Human Exposure to Toxic Metals and Their Associated Health Risk in Selected Land use Settings of Khyber Pakhtunkhwa, Pakistan

Abstract

This study was conducted in order to assess the presence of heavy metals in soil, dust and water along with health risk posed due to the presence of heavy metals. To check the presence of heavy metals in body biological samples like hair, nail, blood and urine were considered. Physical parameters of soil (pH, electrical conductivity, organic matter, and texture of soil) and water (pH, electrical conductivity and temperature) were determined. Five elements were assessed in all the soil and water samples i.e. Cr, Mn, Cd, Ni and Pb. The study was carried out in four different zones of Khyber Pakhtunkhwa (KPK) i.e. urban area of Peshawar, rural area of Mardan, industrial zone of Hayatabad and mining sites present in districts Mohmand and Malakand. Selected metals were quantified using atomic absorption spectrometer. Data was further interpreted for calculation of chronic daily intake, Hazard quotient (HQ) and health risk index (HRI). Distribution maps were prepared through geographical information system (GIS). The samples were also compared with international standards in order to assess the safe limits for all the elements. The results also indicated that maximum elements were within safe permissible limits but still some of the elements were crossing the safe zone specified by the International standards. The values of HQ and HI were <1 indicating the limits within safe range. Looking at the resources of heavy metal contamination, both natural activities and also man-made activities were responsible for it. The concentrations of five selected elements (Cr, Mn, Cd, Ni and Pb) were randomly distributed within study areas. In soil, Ni concentration (3184 mg/kg) was found highest among the selected five elements in mining areas, while Cd (1.5 mg/kg) was lowest in rural areas. In dust samples, Ni again in mining areas was highest (16261 mg/kg), while Cd concentration was lowest (3 mg/kg) xii in rural areas. In water, mining areas were showing highest concentration of Mn (0.12 mg/l), while its concentrations in urban and rural area were below detection limit. One-way Anova was used in order to assess the significant difference present in heavy metals of the selected regions. Among all the elements such as Cr and Ni showed maximum contamination, while Pb showed minimum contamination in soil, dust and water. Biological samples blood, urine, hair and nail were also collected in order to check the presence of heavy metals in human body. Hair and nail were having maximum concentration of heavy metals specifically Cr and Ni while urine and blood were having low concentration of heavy metals. In blood Cr (0.12 mg/l) and Ni (0.12 mg/l) were having high concentrations in mining and industrial area respectively while Pb in blood in rural area was below detection limit. In urine samples collected from industrial area Cr was having mean concentration (0.18 mg/l) while Cd in urine samples collected from rural areas was having least concentration (0.006 mg/l). Hair samples of mining areas were showing mean maximum concentration of Ni (581.5 mg/kg) while Pb concentration in urban, rural and industrial samples was below detection limit. In nail samples collected from mining areas, Ni showed high level of concentration i.e. 157.6 mg/kg while least bioaccumulation was seen of Cd (0.01mg/kg) in mining areas. The reason for low concentration of metals in blood and urine samples might be due to fact that they express short term exposure and bioaccumulation of heavy metals while hair and nail have high level of accumulation because they represent long term exposure. Bioaccumulation trends were also studied in earthworms. Earthworms found in KPK belong to genus Pheritema. Earthworms were kept in the soil of different areas for 14 days in pots then the samples were digested for extraction for extraction of heavy metals. . Heavy metal analysis was done using atomic absorption spectrometer. Analysis using SPSS was done to identify any xiii significant differences between different samples. Unlike the type of soil in which they were placed they responded differently. The concentration of Pb in soil was less in comparison to the concentration of Pb found in the body of earthworm. The maximum quantity was found in earthworm present in industrial soil with a mean concentration of 64.7 mg/kg while in earthworms collected from industrial, mining and urban soil the amount of Ni was negligible. Among selected heavy metals Pb in industrial area showed highest risk i.e. 3.4E-06 while Ni and Cd showed the least risk that is equivalent to zero in water. In soil maximum HI was found in mining soil for Cr i.e. 2.78E+00 while least HI was noted for Cd (2.16E-03) in rural areas. In dust Cr showed maximum HI (7.76E-01) in mining areas while Ni in rural areas showed least HI values (3.36E-04). Overall HI of all the elements was within permissible limits, but still certain elements (Cr and Ni) crossed permissible values according to international limits (CEPA and US EPA). So, monitoring of the sources should be done. Anthropogenic sources should be controlled by government and also by creating awareness among the people. Steps should be taken to regulate the emissions from factories in order to avoid further contamination of environment. Laborers and residents of mining areas are at higher risk because of high pollution load and long exposure time, therefore, these issues should be managed.