Soil arsenic but not rice arsenic increasing with arsenic in irrigation water in the Punjab plains of Pakistan.

Abstract

Irrigating rice with groundwater can lead to As accumulation in soil and rice grains. Matched sets of irrigation water, paddy soil, and rice grains were collected to assess the scale of the problem in the Punjab plains of Pakistan. From a total of 60 sites, irrigation water and rice grains as well as 103 soil samples were collected and analyzed in the laboratory. Irrigation water and 660 soil samples were also analyzed in the field using a field kit. Concentrations of As in irrigation water (65±32 μg/L) are higher in the floodplain of the Ravi River compared to the Chenab (13±9 μg/L) and Jhelum (4±5 μg/L) rivers, as well as the intervening Rechna (6±6 μg/L) and Chaj doabs (0.8±0.2 μg/L). Area-weighted mean soil As concentrations are 12±3 mg/kg along the Ravi, 8.9±2 and 8.1±2 mg/kg along the Chenab and Jhelum, respectively, and 6.2±0.2 mg/kg within the Rachna and 6.1±0.1 mg/kg in Chaj doabs. The As content of polished grains export-quality basmati rice of 0.09±0.05 mg/kg, however, is low across the entire area. Groundwater irrigation leads to elevated As concentrations in paddy soil of some rice-growing regions of Punjab but does not result in increased uptake of As in basmati rice grains.