FFTC Annual Report 2009 7

Seminars and workshops

Development of phytoremediation technology for reducing hazardous

chemical compounds in food

Along with inDustriAl expAnsion, ArAble lAnDs in most Asian countries have been gradually degraded by or contaminated with hazardous pollutants such as cadmium (Cd) and arsenate (As). In the last two decades, this trend became more evident, significantly diminishing the quality of soils and crops and posing great risks to human health and the environment in the region. Recently, Codex Alimentarius proposed a new standard of Cd concentration in major agricultural products such as rice grain, wheat, vegetable, and meat in the hope of better protecting the health of consumers worldwide. Consequently, some countries in Asia modified their standard for critical concentrations of Cd in their soils and crops based on the new Codex standard. With rice being an important staple crop in many countries in the region, reducing Cd concentration in paddy soil and Cd content in rice grains to meet the Codex standard have become an urgent concern. Meanwhile, arsenic water pollution has also become a major problem in many Asian countries such as Bangladesh, China, Vietnam, Cambodia, Myanmar, Nepal, India, and Pakistan. It has been reported that the mechanism of well-water pollution by arsenic is closely associated with agricultural practices, particularly irrigation.

Phytoremediation workshopPhytoremediation is the use of living green plants for in-situ risk reduction and/or removal of contaminants from contaminated soil, water, sediments, and air. Specifically selected or engineered plants are used in the process. With the threat of a serious Cd and As contamination in soil and water in the region, FFTC collaborated with the National Institute for Agro-Environmental Sciences (NIAES), Japan in the conduct of a workshop session on Development of Phytoremediation Technology for Reducing Hazardous Chemical Compounds in Food during the Monsoon Asia Agro-Environmental Research Consortium (MARCO) Symposium held on 05-08 October 2009 in Tsukuba, Japan. Primarily, the workshop aimed to identify and develop reliable, economic, feasible, and effective phytoremediation technology for Cd- and As-polluted soil and water, as well as to propose practical and effective countermeasures in relation to food production.

Status of Cd and As pollution in AsiaAmong the major sources of heavy metal pollution in arable land and in food in the region are natural sources, mining, smelting and flying ash, agrochemicals and fertilizers, sewage sludge applications, and livestock manure use. Nationwide surveys on heavy metal pollution in arable soils have been conducted in Japan, Korea and Taiwan, and are being conducted in China and Thailand. Results of these surveys become the basis for governments to decide on the Maximum Allowable Limit for soil and/or agricultural produce through legislations in controlling and managing heavy metal contamination in food. While As pollution is an important issue that needs to be addressed in Asia where more than 90 percent of world rice production takes place, there has been very limited nationwide survey on As pollution in the region.

Reduction of Cd and As absorption by crops and remediation of heavy metal-polluted arable soilsDuring the workshop, some mitigating measures identified against heavy metal pollution in soil include physio-chemical treatments such as soil dressing, chemical washing, and in-situ stabilization.

8 FFTC Annual Report 2009

Meanwhile, some of the plants identified for use in phytoremediation are as follows: sunflower grown for biofuel; Thlaspi caerulescens and Eichhornia crassipes as hyperaccumulators for soil and water, respectively; rice as a practical remediation crop for low to moderate pollution; and phytoextraction by Sedum plumbizincicola. Use of genetically low Cd species also presents as an effective phytoremediation technology. Some specific studies discussed during the workshop includes: breeding/genetic modification to incorporate low Cd genes without changing other desirable agricultural traits of crops; screening for low Cd genes in rice plant by marker-based approach; and selecting Japonica rice varieties to significantly reduce the Cd uptake in Cd-contaminated soils, especially in low pH and moderately contaminated sites. In terms of physiological approach, some studies cited during the workshop includes: mechanism of Cd uptake by low Cd accumulating species which inhibit or minimize xylem loading; exploring the roles of root function, in which the roots may block Cd penetration into xylem; and investigation on the chemical and physiological characteristics of As as absorbed by rice plants.

Several management practices to mitigate soil and water pollution were also presented.qUse of soil redox status strategy or

water management before and after earing time.

qFertilizer and agrochemical application strategy, as some P fertilizers contain relatively high Cd. Soils low in Fe and Zn enhance Cd uptake by crops, and fertilizers high in Cd increase the mobility (bioavailability) of Cd in soils. Some compost and organic fertilizers may contain large amounts of heavy metals, and should be analyzed before use.

Thlaspi caerulescens (below) and Eichhornia crassipes (right) as potential hyperaccumulators for heavy metal contaminated soil and water, respectively.

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qUse of grafting, particularly eggplant grafted onto S. torvum rootstock, which considerably decreases Cd uptake. Grafting is commonly used to overcome soil-borne diseases such as bacteria and fuzarium wilt, and abiotic hazards such as flooding. It also results to high quality produce, and shows promise in suppressing heavy metal uptake by some cash crops.

qSilicate and phosphorus may effectively decrease As uptake by rice because of their similarity in physico-chemical dynamics and absorption pathways. In Japan, silicate fertilizer has been applied to rice plants for rice blight disease, and this practice is also effective in suppressing As uptake by rice.

Future prospectsWhile phytoremediation is more economically viable and less disruptive to the environment than other methods of remediation, its applications depend greatly on the location of the polluted site, the contaminants in question, and the application methods. The primary goal in phytoremediation is to find plant species which is resistant to or tolerates a particular contaminant with a view to maximizing its potential for phytoremediation. While genetic modification offers enormous potential for phytoremediation in terms of optimizing the tolerance of a species to a particular contaminant, risk assessment in the use of breeding or modern biotechnology for phytoremediation must be of utmost consideration.

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International Workshop on the Development of Phytoremediation Technology for Reducing Hazardous Chemical Compounds in Food

Held in Tsukuba, Japan, 05-08 October 2009 No. of participants: 8 FFTC-sponsored speakers for

Workshop 1: “Development of Phyto-technology for Decreasing Heavy Metal in Food” (One of five workshop sessions under the MARCO Symposium 2009, attended by 180 experts from 12 countries)

Co-sponsor: Monsoon Asia Agro-Environmental Research Consortium (MARCO)/National Institute for Agro-Environmental Sciences (NIAES), Japan

list of FFtC-sponsored papers

1. Impact of use of As-contaminated groundwater on soil As content and paddy rice production in Bangladesh

- John M. Duxbury, Cornell University, USA2. Phytoextraction and management options to reduce

cadmium and arsenic in food crops - Fang-Jie Zhao, Rothamsted Research, Harpenden,

Hertfordshire, UK3. Engineering poplar plants for phytoremediation - Youngsook Lee, Pohang University of Science

and Technology, Korea

Workshop participants visited a Cd-polluted paddy field by untreated drainage water from one of the largest silver mines in Japan.

4. Arsenic in soil, water and plant at contaminated sites and in agricultural soil of Thailand

- Orathai Sukreeyapongse, Land Development Department, Thailand

5. Tolerance mechanisms in cadmium-exposed Eichhornia crassipes Mart. Solms, a phytoremediator

- Gilda C. Rivero, University of the Philippines, Diliman

6. Phytoremediation and the uptake characteristics of different rice varieties growing in Cd- or As-contaminated soils in Taiwan

- Zueng-Sang Chen, National Taiwan University, Taiwan ROC

7. In-situ stabilization of Arsenic-contaminated soil using industrial by-products

- Sang-Hwan, Lee, Mine Reclamation Corporation, Korea

8. Spatial dependency of Arsenic in soils, irrigation water and plants from Arsenic-contaminated tube well used for irrigation in Boro rice cultivation

- Md. Shahjahan Kabir, Bangladesh Rice Research Institute

For further information, contact: Dr. Zueng-Sang Chen, FFTC Technical Consultant