Arsenic occurs naturally in the environment and is present in soil, groundwater and plants. Arsenic occurs in a broad variety of arsenic compounds, of which inorganic arsenic is the most toxic form. In an undisturbed environment under reducing conditions, arsenic-bearing minerals remain stable. Recently, formerly undisturbed environments have been destroyed by the harvesting of surface water and over-pumping of groundwater in many countries. These man-made activities have created an oxidation environment that releases arsenic into groundwater.
There is widespread chronic arsenic poisoning in multiple regions throughout the world, especially in Asia and South America. This occurs because of the consumption of drinking water with geocentrically elevated arsenic. The situation has particularly escalated in densely populated floodplains and deltas, in South and Southeast Asia such as Bangladesh, Nepal, India. While arsenic contamination in drinking water has attracted much attention, plant-based foods are also an important source of arsenic contamination..
Rice is the staple food for around 50% of the world’s population. It is grown widely in South and Southeast Asia with more discrete regional distribution in Southern Europe, Southern U.S., South America, Middle East, and Africa. All soils, including rice paddies, naturally contain the element arsenic. Rice is much more efficient at assimilating arsenic into its grain than other staple cereal crops. Inorganic arsenic and dimethyl arsenic (DMA) dominate grain arsenic speciation. Exposure to inorganic arsenic, a non-threshold class 1 carcinogen, in populations not suffering from elevated arsenic in drinking water is dominated by the consumption of rice.
The concentration of arsenic (As) in rice grains has been identified as a risk to human health. The high proportion of inorganic species of As (Asi) is of particular concern as it is a non-threshold, class 1 human carcinogen.
For the world’s population, rice consumption is a major source of inorganic arsenic (As). Risk posed by inorganic arsenic from rice depends on both the concentration of inorganic arsenic present in the grain and the quantity of grain ingested, moderated by gut bio-availability. Reducing the amount of total and inorganic As within the rice grain would reduce the exposure risk.
We have developed small-scale irrigation systems for vegetable gardening and research is in progress for developing a large-scale system for arsenic-free agricultural irrigation.