Occurrence of arsenic in the surface and ground water of farm villages near Hanoi, Vietnam, and factors relating to it

Whether the arsenic occurred in the surface and ground water (irrigation canal/pond and well water) and if so, what caused the occurrence were examined in the three farm villages near Hanoi, Vietnam, where chemical fertilizer had been intensively applied to farmland during cropping. Water sampling was done in March 2004, and the arsenic concentration, pH and ORP in the water were measured by inductively coupled plasma-mass spectrometry, and portable pH and ORP meters respectively. The arsenic was detected in both surface and ground water with maximum concentrations of about 20 and 16 mg/m3, respectively. However, the concentrations in the ground water were less than the WHO's drinking water quality guideline (10 mg/m(3)) as a whole, showing no urgent health risks from drinking the ground water. For the surface water, the inflow of arsenic-containing phosphate fertilizer from farmland to irrigation canals and ponds was assumed as the cause of arsenic occurrence, because the farmland was spread over the target area and the surrounding areas. However, in the ground water, the level of arsenic concentration was not in alignment with that of the phosphate fertilizer amount applied to the three villages. Therefore, it is unlikely that the arsenic in soil was eluted to ground water through exchange with phosphorus in the fertilizer. Even though some arsenic elution from soil occurred, its amount was not significant. This was backed by the lack of correlation between arsenic concentration and pH/ORP. In addition, the arsenic concentration of the ground water was not much higher than that of the surface water. Therefore, the arsenic in the ground water perhaps originated from percolation by arsenic-containing surface water. Significant differences in the arsenic concentrations of the ground water were observed among villages, reflecting the differences in villages' physiographic and hydrographic conditions.