Assessment of water quality and trace metal contaminations in Mondolkiri province in the Northeastern part 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.

Assessing the fractionation and bioavailability of heavy metals in soil-rice system and the associated health risk

This study developed a method to build relationships between chemical fractionations of heavy metals in soils and their accumulations in rice and estimate the respective contribution of each geochemical speciation in the soils from the Yangtze River Delta, China. In contaminated areas, residue and humic acid-bound fractions in soils were the main phases for most heavy metals. The mobility of heavy metals was in this following order: Cd > Pb ≈ Zn > Ni > As ≈ Cr > Hg. Transfer factors calculated by the ratios of specific fractionations of heavy metals in the soil-rice system were used to assess the capability of different metal speciation transfer from soil to rice. The carbonate and Fe/Mn oxyhydroxides bound phase had significant positive correlations with total metal concentrations in rice. Hg uptake by rice might be related to the exchangeable and carbonate-bound fractions of soil Hg. Results of PCA analysis of transfer factors estimated that the labile fractions (i.e. water soluble, exchangeable and carbonate bound) contributed more than 40% of the heavy metal accumulations in rice. Effect of organic matter and residue fraction on metals transfer was estimated to be ~ 25 to  ~ 30% while contribution of humic acid and Fe/Mn oxyhydroxides-bound fractions was estimated to be ~ 20 to  ~ 30%. Modified risk assessment code (mRAC) and ecological contamination index (ECI) confirmed that the soil samples were polluted by heavy metals. Soil Cd contributed more than 80% of mRAC. Contrarily, the main contributors to ECI were identified as As, Hg, Pb and Zn. The average values of total target hazard quotient (TTHQ) and Risk_total were above 1 and 10^-4 respectively, implying people living in the study area were exposed to both non-carcinogenic and carcinogenic risk. As and Pb were the main contributor to high TTHQ value while As, Cd and Cr in rice contributed mostly to Risk_total value. Spatial changes of ecological risk indexes and human health risk indexes showed that the samples with high TTHQ values distributed in the area with high values of mRAC. Likewise, the area with high ECI values and with high carcinogenic risk overlapped.