Metal contamination of rice supplies in Asia

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There has recently been much public debate about contamination of rice supplies across Asia with heavy metals. Two elements in particular are discussed: arsenic (As) (which is strictly a metalloid not a metal) and cadmium (Cd). Rice is thought to be one of the main sources of As in the human diet, and chronic As exposure is linked to cancers of the skin, lung, bladder and prostate as well as heart disease. Contamination of rice fields with As has been found in many parts of Asia, especially in the heavily-populated deltas of the Ganges and other rivers draining from the Himalayas whose rocks contain it. The solubility of As in soils - and hence the ease with which it is absorbed by plant roots - increases when a soil is flooded for paddy rice production because of changes in soil chemistry linked to redox conditions. Hence the particular link between rice and As. Cadmium is also a primary carcinogen and a chronic nephrotoxin. Sources of Cd in rice soils include parent rock materials and base-metal mining and industrial discharges up-stream of rice field water supplies. In contrast to As, the solubility of Cd tends to decrease when a soil is flooded for rice production, again linked to changes in redox chemistry. But conversely, if the soil is drained during the growing season, as for example in water-saving irrigation systems that are becoming widespread in various parts of Asia, Cd solubility and hence plant uptake tend to increase. So there is concern that water-saving irrigation technologies may exacerbate Cd contamination risks. There is also concern that new varieties of rice with enhanced uptake of micro-nutrients such as zinc, for the sake of human nutrition, may also take up more Cd. However, the extent of these metal contamination risks across Asia is not well understood. Because of the complex mix of processes and variables controlling metal uptake, making predictions across diverse rice environments is difficult. In the absence of reliable assessments of the extents the problem, it is difficult to prioritise research to develop technologies to lessen contamination risks, though there are promising possibilities for doing this through rice breeding and agronomic management. There is therefore a pressing need for better estimates of contamination risks in the different rice environments across Asia.In this project we propose to develop methods with which to do this based on spatial data analysis and modelling. We will develop models for predicting contamination levels in rice grain based on spatially-resolved data on environmental, management and genetic variables. We will use the latest spatial data analysis and modelling techniques for this. To develop our models, we will make pilot studies in Bangladesh and the Philippines, in which we will conduct surveys of contamination and its drivers over relevant geographic areas. Our reasons for choosing Bangladesh and the Philippines are related to the availabilities of relevant spatial data resources in these countries, and favourable political conditions for studies on rice contamination in these countries. We will seek to widely disseminate the project findings and the generic methods we will develop through the project team's wide network of partnerships within target countries and across scientific disciplines.