Cadmium Contamination and Its Risk Management in Rice Ecosystems

Cadmium (Cd) has been identified as one of the major heavy metals reaching the food chain through various geogenic and anthropogenic activities. In many East and South Asian countries including Japan, Bangladesh, Indonesia, and Korea, Cd accumulation in rice (Oryza sativa L.) ecosystems and its subsequent transfer to the human food chain is a major environmental issue. Rice soils in these countries have been affected by Cd accumulation derived from fertilizer and manure application, mine tailings, and refining plants. Excessive intake of Cd into the human body is detrimental to human health, causing serious illnesses such as itai-itai disease. To ensure the safety of foods, the concentrations of Cd in staple crops should be below a standard value; this applies particularly to rice because 34-50% of the Cd intake by people in many Asian countries has been derived from rice. Therefore, development of remediation methods for Cd-contaminated rice soils has become an urgent task to ensure food safety. This chapter provides an overview of the various sources of Cd in rice ecosystems and the biogeochemical processes that regulate Cd bioavailability to organisms, including microbes, plants, animals, and humans. Because of the complexity involved in dealing with Cd in rice ecosystems, exacerbated by the Cd source, site characteristics, and the nature of water management strategies, we have attempted to describe an " integrated" approach that employs a combination of remediation technologies, with the aim of securing methods that are economically and technologically viable.