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( Zueng Sang Chen ) 한국환경농학회 2012 한국환경농학회 워크샵자료 Vol.2012 No.2
The heavy metal regulation (digested by aqua regia) of agricultural soils in Taiwan are listed as (mg/kg): As 60, Cd 5, Cr 250, Cu 200, Hg 5, Ni 200, Pb 500, and Zn 600. The upper levels of background total concentration of heavy metals in surface soil (0-15 cm) in Taiwan are listed as (mg/kg): As 18, Cd 2, Cr 50, Cu 35, Hg 0.4, Pb 50, Ni 50, and Zn 120 (Taiwan EPA, 2012) http:// sgw.epa.gov.tw/public/En/Default.aspx. The heavy metal regulations in vegetables in Taiwan are listed as (mg/kg, fresh weight basis): Cd 0.2 (leaf vegetables), Cd 0.1 (root and stem vegetables), Cd 0.05 (fruit vegetables), Pb 0.3 (leaf vegetables), Pb 0.3 (root and stem vegetables) and Pb 0.1 (fruit vegetables). The mean water contents in rice is 13% and in vegetables is 90%. http:// dohlaw.doh.gov.tw/Chi/FLAW/FLAWDAT0202.asp About 472 ha of rural soils in Taiwan were contaminated by the discharged wastewater from industrial parks, especially in the western regions of Taiwan, and 126 ha of rural soils are still contaminated now. The metals pollutants, major on Cd, Cu, Zn, Pb, Cr, Ni, were absorbed in the surface soils of 0-30 cm depth of rural soils. The rice was contaminated by the rural soils and affected the food safety through food chain process. The main factors affecting the metals uptake by crop are the concentrations and speciation of the metal in the soil solution released from different soil characteristics, and its translocation from root to the shoot and grain. Soil key factors controlling metal soil bioavailability are soil pH, sorption of metals on the particle surfaces (clay or oxides minerals) and soil redox potential depending on the water management by flooding or drainage. Applying lime materials to increase soil pH and to reduce the metal solubility into soil solution can significantly reduce the metals uptake by rice or vegetables in the metals-contaminated soils. The occurrence of Cd-polluted rice usually depends on soil properties, especially on soil pH, the contents of clay and iron oxides, and water management. There is no clear relationship between Cd in soil and Cd in brown rice in Japan, Korea and Taiwan, however, the Cd concentration of brown rice grown in contaminated soils is much higher than that in the uncontaminated soil. For different rice species, the Indica rice varieties significantly absorbed more Cd than Japonica rice varieties grown in slight or serious Cd-contaminated sites in Taiwan. The relations between copper (or zinc) concentration of brown rice and soil bioavailability of copper (or zinc) extracted by 0.1M HCl in contaminated soils meet the “plateau theory”. There is no significant increase on Cu (or Zn) in the brown rice grown on the contaminated sites, but the rice productivity is significantly reduced at least 20-50%. The arsenic bioavailability of Gang-Du Plain soils near Taipei, total As content in 63 ha of rural soils ranged 60-545 mg/ kg, are significantly controlled by the amounts of amorphous Fe and Al oxides of volcanic soil characteristics. The As concentration of brown rice ranged 0.15-0.35 mg/kg and there are no any toxic symptom and productivity problem at this site. Arsenic concentration in vegetable can be predicted by extraction method with 0.5 M sodium bicarbonate. In conclusion, the amounts of the metals of the crops are affected by soil properties, metal adsorption ability, and rice or vegetables species. Soil amendments significantly reduce the Cd uptake of brown rice, especially applied by lime materials. The concentrations of As, Cd and Zn in the brown rice are relative higher than those of other countries. For different rice species, the Indica rice varieties significantly absorbed more Cd than Japonica rice varieties in slight or serious Cd-contaminated sites in Taiwan. The metal concentration (As, Cd, Cu and Zn) of brown rice and vegetables can be mostly predicted by soil bioavailability extracted with different extraction solution.
( Zueng-sang Chen ) 한국환경농학회 2016 한국환경농학회 학술대회집 Vol.2016 No.-
More than 1000 ha of rice grown soils were seriously contaminated by heavy metals caused by illegal waste water discharged from industrial parks, especially by arsenic (As), cadmium (Cd), copper (Cu), and zinc (Zn) in last two decades in Taiwan. Taiwan scientists had different experience on soil remediation techniques including applying liming materials, turnover dilution and acid washing for different levels of Cd-contaminated soils (10-60 mg/kg). Phytoremediation is one of other technologies for multi-heavy metals contaminated soils in Central Taiwan. Taiwan scientists have developed various Cd uptake prediction models were applied to predict the Cd accumulation of 12 rice varieties, soil pH and total Cd concentration in the rice field. Overall, median Cd concentrations of brown rice of Indica rice varieties were 2 to 3 times higher than those of Japonica rice varieties, no matter the rice grown in low or high Cd-contaminated fields. Higher variation was found in the concentration of Cd of Indica brown rice compared with those of Japonica brown rice. Different soil amendments (addition of 2.5% rice husk or phosphorus materials with three phosphorus (P) levels in 150, 525, 900 kg P2O5 per ha) and different soil water management (flooding or saturation condition) were compared to reduce the health risk of rice grown in different soils contaminated with arsenic (As) in Taiwan. The saturation water management with flooding except keeping drainage for 10 days after maximum tiller stage can significantly reduce total As concentration of brown rice by increasing the soil redox potential (Eh) and reducing the As concentration of pore water, compared with the flooding treatment (p<0.05). The addition of husk can significantly affect soil drainage condition at early stage, but this treatment also increased the reduced condition to produce higher As concentration of brown rice. The As speciation distribution of total As of brown rice indicated the arsenite ion (As(III)) concentration always ranged in 0.2 to 0.3 mg/kg and the other major As speciation of brown rice are dimethyl arsenic acid (DMA), which is much less health toxicity than arsenite ion of brown rice. The total As concentration of soil pore water or brown rice were no significant difference among different P treatments. The significant decreases of As concentrations of rice straw can be found after P application at 900 kg P2O5 per ha in the clayey soil (p<0.05), only under saturation water treatment. In the clayey red soil, As concentration of rice straw or brown rice was significantly decreased under saturation water treatment compared with flooding treatment (p<0.05). The total As of brown rice was not significantly decreased by different P levels treatments. There are significant correlation between total As and DMA of brown rice (p<0.01). Arsenite ion (As (III)) concentration of brown rice always keep 0.2-0.3 mg/kg in different treatments. Although total As concentration of brown rice higher than 1.0 mg/kg in the clayey soils or treatments, but arsenic species was predominated by dimethyl arsenic acid (DMA). This study indicated that the inorganic arsenite ion (As (III)) concentration of brown rice is a major concerned risk criteria. Codex Alimentarius Commission (Codex) has adopted that the maximum permissible concentration of As of brown rice should be evaluated as inorganic arsenite ion (As (III)), not total As concentration level.