Over the past decades, the source of drinking water in Bangladesh has been largely shifted from surface water to groundwater and more and more ground water is being used for the irrigation of paddy rice to meet the increasing food demand. Only in 1998 has it been established that 40-50% of the abstracted groundwater in Bangladesh contains arsenic at concentrations above the WHO drinking water guideline (10 µg/L). 30-50 million people in Bangladesh are estimated to consume drinking water with>50 µg/L As. More than 100’000 cases of As poisoning have been >documentedso far. In addition to the immediate threat from the consumption of As-rich drinking water, arsenic input into soils may lead to additional long-term risks for the environment and human health. Arsenic may accumulate in surface soils and eventually decrease the crop yield.
Arsenic taken up by rice plants additionally increases the arsenic burden to the local population. Numerous biogeochemical processes affect the cycling of arsenic in the paddy soil - rice plant system. However, the relative importance of these processes and their effect on the fate and impact of arsenic are only poorly understood.
In this context, we perform a combined field and laboratory study involving two research teams in Switzerland (EAWAG and ETHZ) and researchers from the Bangladesh University of Engineering and Technology (BUET). One part of the project consists of an extensive field study in the village of Srinagar 30 km south of Dhaka, where we collect extensive data on the fate of arsenic in the irrigation and flood water and its distribution in the paddy fields and the uptake by rice plants. The second part of the project consists of well-controlled laboratory experiments related to the biogeochemistry of arsenic in the studied field system. The aim of these laboratory studies is to gain a detailed understanding of the most relevant biogeochemical processes that control the fate of arsenic at the field scale.
The project is the basis for two dissertations. One PhD student working at the EAWAG focuses on transformation processes of arsenic in the irrigation and flood water at the field site and performs laboratory studies on the chemical interactions of arsenic at mineral surfaces. The second PhD student working at the ETH investigates the spatial and temporal variations of the arsenic concentration in the field soils and in paddy rice and performs complementary laboratory experiments on the reduction and oxidation of As in paddy soil and the uptake of As by rice.This project will provide detailed information on the fate of As that is transported into rice fields by irrigation. Detailed investigations of the relevant biogeochemical processes will lead to a better understanding of the key reactions that determine the spatial distribution and the temporal behavior of arsenic in these soils and its uptake by rice. Based on the quantitative understanding of the relevant processes, better predictions of the long-term fate of arsenic in irrigated paddy soils will be possible.