New aspects of collaborative research on the soil pollution, food safety and soil remediation techniques in Asia

Soil pollution and food safety are major challenges to be discussed in Asia resulting from previous industrial development without suitable regulations. In recent years, a comprehensive survey to understand the distribution of heavy metal contaminated soil nationwide was conducted in many Asian countries, and Taiwan’s experiences and related databases are described in this review. Rice is the staple food in Asian countries, but many paddy soils were contaminated by illegal discharges of waste water from local factories. Results from field studies in Taiwan showed that rice variety and soil Cd concentration are major factors affecting edible rice safety: the Indica type rice absorbed significant more Cd from contaminated soil than Japonica type, and most contaminated brown rice and polished rice was found when the soil Cd concentration extracted by HCl was higher than 2 mg/kg. No relationship could be found between soil Cd and brown rice Cd. The Cu and Zn concentrations in brown rice were in a fixed range under a wide range of soil Cu and Zn, and the relationships meet the plateau theory which theCu and Zn concentration of rice is not proportion to the increase of that in the soil. Whenthe total Cr and Ni concentration of rural soils reached 250 and 600 mg/kg, the rice yield will reduce but the Cr and Ni concentration inpolished rice were less than 4 and 14 mg/kg, respectively. In paddy soil and rice uptake system, Pb solubility and mobility is very low, however, the rice yield will reduce 20% as soil total Pb approached 2,000 mg/kg. When the total As concentration of rural soil reached 60 mg/kg, the rice productionwill be significantly reduced. To explain the relationship between heavy metal concentration in soil and plants, six hypotheses (i.e. single-metal abrupt toxicity threshold, soil-plant barrier, clean sludge concept, uptake plateau concept, aging effect, and absence of evidence) were proposed from previous research findings. The regulations of heavy metal in contaminated soils, the main reasons of the development of legislations, andthe strategies for monitoring and remedial actions in USA, UK, Netherlands, Germany, Japan, China, and Taiwan were also compared in this article. Finally, concerning the high toxicity and mobility of Cd, its transmission in food chain and the human intake of Cd from all pathways were also analyzed.