Chemical Analysis of Arsenic in Environmental and Biological Samples of Selected Areas of Sindh, Pakistan and its Removal from Water

Abstract

The river, canal, tube well, hand pump and municipal water samples were evaluated as possible sources of arsenic (As) contamination in different districts of Sindh, Pakistan. The total arsenic (As) contents in surface and ground water samples were evaluated. The arsenic concentrations in surface and ground water samples from the two areas of Sindh under study (Jamshoro, Khairpur, Sukkur and Hyderabad) were found in the range of 4.2-18 and 9.20-361 μg L-1, respectively. The underground and in some surface water total arsenic exceeded the WHO provisional guideline values 10 μg L-1 and reached upto 362 μg L-1. It was observed that hand pumps and tube well water samples have high level of arsenic than canal, river and municipal water samples. This is due to widespread water logging from Indus river irrigation system, which causes high concentration of salts in this semi-arid region and results in enrichment of As in shallow groundwater. Besides total As other physicochemical parameters, nitrite, nitrate, chloride, sulphate, sodium, potassium, calcium, magnesium and iron were evaluated for the quality and safety assurance of drinking water. Among them iron, calcium, magnesium and sulphate were observed to be higher than WHO recommended level. In addition of total arsenic, its inorganic speciation in water samples from the different districts was evaluated. The inorganic As species (As3+ and As5+) were separated from organic forms by adsorbing on alumina (Al2O3) where as the organic As was elute out. The retained inorganic As species was eluted by 0.2 M HCl. Then trivalent and pentavalent arsenic in the eluent were complex with molybdate and ammonium pyrrolidinedithiocarbamate (APDC), respectively. Then the trivalent arsenic - APDC and the pentavalent arsenic molybdate complexes were quantitatively extracted into Triton X-114. The main factors affecting the separation and cloud point extraction (CPE) were investigated in detail. Total inorganic As in collected water samples was determined by using titanium dioxide (TiO2) as adsorbent. The standard spiking method was used for validation and the %recoveries of As species were found in the range of 98 - 99%. The mean concentrations of inorganic trivalent and pentavalent arsenic in the surface water and ground water samples were ranged from 3.00-53.0 and 6.00-352 μg L-1, respectively. Principal component analysis scores allowed the samples to be classified by cluster analysis. Principal component analysis of the data from the hand pump samples and from the well tube samples showed two significant components were responsible for sixty percent of the variance. A single-step extraction procedure (S-BCR) was developed and validated as a replacement for the BCR sequential extraction procedure (BCR-SES). The same reagents and operation conditions are used procedures. The single-step extraction procedure was applied to investigating arsenic partitioning sediments samples, collected from lake, canals and river of district Jamshoro, Pakistan. The results obtained for As with single step extraction were compared to those obtained from BCR-SES and validated using CRM-BCR 701. There was no significant difference in extraction efficiency between S-BCR and BCR-SEC for arsenic content at 95% confidence limit. The precision of the proposed S-BCR (expressed as % RSD) was lower than 10 %. The sediment samples collected from different ecosystem have different physico- chemical characteristic and As content. The arsenic mobility of the samples collected from the various locations was found to decrease in the order: acid soluble fraction > oxidizable fraction > reducible fraction. The fraction of As dissolving in 0.11 mol L-1 acetic acid was higher in the lake sediment samples as compared to those sediment samples obtained from river and canal, showing the contamination of lake. To evaluate the uptake of arsenic by crops (vegetables and grain), they were grown in agricultural soil irrigated for long period with tube well water containing high concentrations of arsenic and their arsenic contents were compared to crops of same species grown in soil irrigated with canal water Having a much lower arsenic concentration. In addition, the total and EDTA (pH 7) extractable As soils irrigated with tube well and canal water were determined and correlated with total concentrations of As in edible parts of vegetables. Statistically significant correlations were obtained between the total and EDTA extractable fractions of As in soil. The high level of total and EDTA extractable As were found in tested samples as compared to controlled samples. This investigation highlights the increased danger of growing food crops in the agricultural land continuously irrigated by As contaminated water. The effects of As exposure via drinking water was evaluated by analysis of As levels in scalp hair of children (age < 10 year) and adults (16-45) years of both gender collected from sub districts of Khairpur, Pakistan having different As contents in surface and underground water. For comparative purposes scalp hair samples of age-matched children and age matched adults were also collected from an area having low level of As (<10 μg L-1) in drinking water. The As concentrations in scalp hair samples of subjects belonging to non exposed, less exposed and high As exposed areas were found in the range of from 0.01 – 0.27, 0.11-1.31 and 0.36-6.80 μg g-1, respectively. 20% of total children belong to high As exposed area have skin lesion on their hands and feet. A positive correlation coefficient (r = 0.91 - 0.99) was obtained between As contents in drinking water and scalp hairs of children and adults of areas investigated The arsenic hazard quotient was estimated on the basis of the arsenic concentrations in drinking water and scalp hair of the male subjects in both age groups consuming drinking water in the study areas. A toxicity risk assessment provides a hazard quotient corresponding to <10, indicates non- carcinogenic exposure risk from the consumption of drinking water in the study areas. For remediation of As from water samples indigenous materials (stem and leave) of Acacia nilotica have been studied. The effects of various parameters vis, pH, biosorbent dosage, temperature and exposure time for bio-sorption of As were investigated in detail. The resulting data were evaluated using Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. It was observed that As biosorption best fit the Langmuir and Freundlich isotherms. The free energy of transfer (E) calculated on the basis of D–R model, indicated physico-chemical biosorption. The thermodynamic study indicated that the bio-sorption mechanism was endothermic, spontaneous and feasible for As removal. The kinetics of As biosorption was better interpreted by pseudo-second-order rate equation with good correlation coefficients. The removal of As by biomass of A. nilotica was > 95% at the concentration level of As < 200 μg L-1 of As solution. The uptake capacity of the biomass studies was 50.8 mg As g-1.