Yang, JE; Ok, Y; Kim, W; Lee, J
This paper reviews the status of heavy metal pollution in paddy soils and rice in Korea, the human health risk assessment for heavy metals, and the remediation approaches to reduce the metal transfer from soil to rice grain. The Soil Environment Conservation Law (SECL) designates the soil pollution standards for As, Cd, Cu, Hg, Cr6+, Pb, Ni, Zn and F, and these are used as the maximum permissible levels in agricultural soil. The extensive monitoring of heavy metals in soil and crop revealed that concentrations of metals in paddy soils, without an evident anthropogenic source of contaminants, were mostly below the threshold levels designated by the SECL. Major sources of metal pollution in paddy soils, however, were related to mining activities. The increased level of Cd and Cu in soil increased the activities of cations (Ca>Mg>K), temporally decreased the level of exchangeable cations, altered the supply mechanisms, and decreased the nutrient buffering capacity of soil. The most widely described effects of metal toxicity in plants were stunted growth, leaf epinasty and chlorosis. The Korean Government implements various countermeasures to prevent soil pollution of metals through legislation, monitoring networks, risk assessment and remediation. The potential adverse effects of metals on human health were assessed based on human exposure pathways to rice, groundwater and soil in three abandoned mines where metal contents in soil and rice exceeded the safety guidelines. The hazard index (HI) values for As and Cd exceeded 1, representing a potential toxic risk of As and Cd to human health. The cancer risk for As via rice and groundwater consumptions exceeded one cancer case in 10 000. Health risk assessment indicated that long term exposure to rice grown in metal-contaminated paddy soils could pose a potential health threat. Soil and plant management options have been considered to prevent heavy metal transfer to rice from contaminated paddy soils. Soil management options include using soil ameliorants, fertilizers and irrigation control, soil covering/dressing, reversing, and soil layer mixing methods. In plant management options, 24 rice cultivars were screened to find the accumulating or excluding variety. The Japonica cultivars were considered to accumulate low level of Cd. These cultivars may be tested by planting them in a contaminated soil environment to achieve the metal concentration low enough for safe consumption. Transfer of Cd into rice from contaminated paddy soils could be lowered up to the regulatory level through zero-valent iron and lime. Through Cd immobilization, it reduced Cd concentration in soil solution and altered the bioavailable fraction of Cd into non-available one. The continuous submersion of the soil interacted better with fertilizer than with the intermittent irrigation to retard the Cd uptake by rice. Based on the regulatory criteria of Cd for soil pollution and food safety, the quantity of Cd which should be remediate at most was estimated to be only 0.04% in the contaminated soils.
agricultural soils; arsenic; buffering capacity; cadmium; chlorosis; chromium; copper; epinasty; fluorine; groundwater pollution; heavy metals; lead; leaves; mercury; nickel; phytotoxicity; plant disorders; polluted soils; public health; remediation; rice; soil amendments; soil management; soil pollution; soil types; zinc; Korea Republic; Oryza; Oryza sativa; East Asia; Asia; Developing Countries; Threshold Countries; OECD Countries; Poaceae; Cyperales; monocotyledons; angiosperms; Spermatophyta; plants; eukaryotes; paddy; South Korea; Field Crops (FF005) (New March 2000); Plant Physiology and Biochemistry (FF060); Plant Production (FF100); Plant Disorders and Injuries (Not caused directly by Organisms) (FF700); Plant Toxicology (FF800); Soil Chemistry and Mineralogy (JJ200); Soil Physics (JJ300); Soil Fertility (JJ600); Fertilizers and other Amendments (JJ700); Soil Management (JJ900); Human Health and the Environment (VV500); Industrial Wastes and Effluents (XX400)