Environmental arsenic epidemiology in the Mekong river basin of Cambodia

Chemical risks in drinking water of inhabitants in the basin of the Tonle Sap Great Lake

The present study aimed to assess chemical risks in the drinking water of inhabitants in the basin of the Tonle Sap Great Lake. Water samples from tube wells (n = 52), dug wells (n = 13), stored rain water (n = 39), ponds/lakes (n = 19), canals/rivers (n = 24), and household pipe water (n = 45) were collected and analyzed for physicochemical properties, as well as microbial and chemical qualities using standard methods. Analytical results revealed that 42.1% of tube wells had As > 10 μg L-1 while 8.3% had Cr > 0.05 mg L-1. Concurrently, 55.2 and 11.8% of tube wells had Cd > 3.00 μg L-1 and Pb > 10 μg L-1, respectively. Moreover, 35.0% of pipe water had Fe > 0.3 mg L-1, whereas 85.7% of tube wells and 69.2% of dug wells had Mn > 0.1 mg L-1. All water sources including pipe water could pose risks of non-carcinogenic effects of chemical mixtures to all exposure groups through their drinking water pathway. Children were at a higher risk of chemical mixtures in their drinking water than adults. This study suggests that advanced treatment technologies should be applied to the current water treatment plants to provide inhabitants with safe drinking water.

Distribution and hydrogeochemical behavior of arsenic enriched groundwater in the sedimentary aquifer comparison between Datong Basin (China) and Kushtia District (Bangladesh)

A prompt growth in research on arsenic occurrence and behavior in the environment has occurred over the last decade or so. High arsenic (As) in groundwater has become a major global concern due to its widespread occurrence. A comparative hydrogeochemical study was performed on the occurrence of high As groundwater in Datong Basin, China, and Kushtia District, Bangladesh. A total of 132 groundwater samples (83 from Datong Basin and 49 from Kushtia District) were collected to analyze the major hydrogeochemical components and trace elements in groundwater of both areas. Factor analysis (FA) was applied on the hydrochemical data to identify the major hydrogeochemical processes in sedimentary aquifers. High As groundwater was observed in the low-lying central parts of Datong Basin, which are composed of the Holocene alluvial and lacustrine aquifers. The elevated As concentrations ranged from 0.31 to 452 μg/L and distributed in depths between 20 and 45 m. As-enriched groundwater is mainly Na-HCO₃ type water and characterized by higher pH value, high Na⁺, low Ca²⁺, SO₄^2-, and NO₃^- along with moderate TDS. The alkaline and reducing subsurface environment facilitate the leaching of As in sedimentary aquifers. The release and distribution of As in aquifers are resulted from the reduction of As-carrying crystalline iron (Fe) oxide/hydroxides and oxidation of organic matter. The aquifers of Kushtia District, Bangladesh, are unconsolidated, alluvial in nature, and developed from Holocene floodplain and Pleistocene deposits. High As (6.04-590.7 μg/L) groundwater occurs mainly in shallow aquifers. The Ca-HCO₃ type groundwater is distinguished by circum-neutral pH, medium-high EC, high HCO₃^-, and low content of NO₃^-, SO₄^2-, K⁺, and Cl^-. The reductive suspension of MnOOH increases the dissolved As loads and redox responsive elements such as SO₄^2- and pyrite oxidation act as the main mechanisms for As release in groundwater. As is mobilized by anaerobic leakage from the brown-clay and gray-sand into the sediment. Infiltration from irrigation return and surface wash water are the potential factors that remobilize As. The weak loading of Fe suggests that the release of Fe and As is decoupled in sedimentary aquifers of Kushtia District.

Arsenic and Other Metals' Presence in Biomarkers of Cambodians in Arsenic Contaminated Areas

Chemical analyses of metal (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ba, and Pb) concentrations in hair, nails, and urine of Cambodians in arsenic-contaminated areas who consumed groundwater daily showed elevated levels in these biomarkers for most metals of toxicological interest. The levels of metals in biomarkers corresponded to their levels in groundwater, especially for As, whose concentrations exceeded the WHO guidelines for drinking water. About 75.6% of hair samples from the population in this study contained As levels higher than the normal level in unexposed individuals (1 mg·kg⁻¹). Most of the population (83.3%) showed As urinary levels exceeding the normal (<50 ng·mg⁻¹). These results indicate the possibility of arsenicosis symptoms in residents of the areas studied. Among the three biomarkers tested, hair has shown to be a reliable indicator of metal exposures. The levels of As (r² = 0.633), Ba (r² = 0.646), Fe (r² = 0.595), and Mo (r² = 0.555) in hair were strongly positively associated with the levels of those metals in groundwater. In addition, significant weak correlations (p < 0.01) were found between levels of exposure to As and As concentrations in both nails (r² = 0.544) and urine (r² = 0.243).