Metal contamination of rice supplies in Asia

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.

We will develop models for predicting contamination levels of individual metals and metalloids in rice grain based on spatially-resolved data on environmental, management and genetic variables.

To develop our models, we will make pilot studies at 600 farm sites in Bangladesh and the Philippines (300 in each country), in which we will conduct surveys of contamination levels and its drivers. We chose these countries based on availabilities of relevant spatial data and favourable political conditions for studies on rice contamination. The sites will be chosen to cover relevant geographic areas with a range of contamination risks and rice growing variables. Farmers will be interviewed for their soil and water management practices and socio-economic factors. Rice grain and soils will be sampled: grain will be analysed for metal contents and DNA finger-prints to derive genotype information; soils will be analysed for standard properties and metal contents.

We will also collect existing spatial data on biophysical conditions (soils, water, geology), pollution risks (geogenic, anthropogenic) and rice growing conditions across Bangladesh and the Philip[pines. We will combine this mapped data with the survey and analytical results to derive models relating contamination risks to driving variables (environment, management and germplasm), informed by understanding of the plant, soil and water processes governing uptakes of different metals. We will develop the models on a stratified random subset of the data, and use the remaining data for validation. We will use the models to predict contamination risks across Bangladesh and the Philippines. We will draw conclusions for generic methods for making assessments in other rice-producing countries in Asia.

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.

In addition to the academic beneficiaries listed above, the project will benefit rice breeders and agronomists concerned with genetic improvement of rice varieties and related management practices to mitigate metal contamination risks. In the medium- and longer-term, the project will benefit rice producers and consumers, particularly those in areas with metal-contaminated soils, and rice exporters.

By the end of the project we will have developed generic methods for assessing metal contamination risks in different rice environments. We will facilitate the adoption of these methods through existing technology-transfer programmes that the project team are involved in.

Relevant technology-transfer programmes involving the project team are: the CGIAR HarvestPlus programme, concerned with micronutrient malnutrition and biofortification in crops; the Cereal Systems Initiative for South Asia (CSISA), for accelerated development and deployment of new varieties, management technologies and policies for cereal systems in South Asia; and Stress-tolerant Rice for Africa and South Asia (STRASA) concerned with varieties and technologies for rainfed rice systems. Each of these has components for germplasm testing with farmers, followed by seed multiplication, distribution and impact evaluation.

The project's findings will be will transferred to breeders and agronomists through direct interactions with members of the project team. The main route for dissemination to other scientists will be through publications in high impact journals and presentations at international conferences. All members of the project team have strong track records in publishing in top-ranked journals in their areas and in broad-reach journals. We will make all datasets and models produced in the project available to other researchers, following publication of papers, via websites at the project team's host organizations.

The project team has strong links with rice policy makers in Asia and globally. We will exploit these direct contacts. We will produce regular reports for websites and newsletters of our respective organizations, to communicate with policy makers and the general public.