Cd and As contamination of agricultural products and countermeasures in Japan

Many heavy metals exist in minute amounts in natural agricultural soil. However, when their amounts exceed a certain level due to pollutants brought from outside, soil contamination occurs and agricultural products become contaminated. There have been many cases in Japan of heavy metal contamination originating from old mines and smelters, and soil contamination of agricultural land has become a social issue. In particular, cadmium (Cd) is one of the most harmful heavy metals. If agricultural products absorb an excessive amount of Cd, they may adversely affect people’s health, and therefore allowable concentrations are regulated by law. If agricultural land has become contaminated with Cd, measures for minimizing the absorption of Cd by agricultural crops are necessary; these include: (1) soil dressing, (2) water management (paddy field), (3) chemical cleaning of soil, (4) phytoextraction, and (5) use of different varieties and rootstock. Rice consumption is not only a major source of Cd but also that of arsenic (As) for the population of Asia. Flooding of paddy fields is effective in reducing grain levels of Cd; however, anaerobic conditions in paddy soil lead to As mobilization and, therefore, As uptake by rice could increase. A new study has been launched investigating whether As and Cd concentration in rice grains can be lowered simultaneously by controlling irrigation water and by using a rice cultivar with low Cd uptake, along with agricultural materials.