World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Monday, 10 July 2006 - Friday, 14 July 2006
158-17

This presentation is part of 158: 3.5C Combating Global Soil & Land Degradation III. Agro- and Forest Ecosystems: Physical, Chemical and Biological Processes - Poster

Toxicities of Soil Cadmium towards Wheat Triticum aestivum and Its Bioremediation Potential.

JUN GONG, CK Life Sciences Limited, 2 Dai Fu Street, Tai Po Industrial Estate, Tai Po, N.T., Hong Kong, China and Siu-Wai Chiu, Dept of Biology, The Chinese Univ of Hong Kong, Shatin, New Territories, Hong Kong, China.

Soil pollutants affect the yield of crops, and if bioaccumulated, the contaminated crop poses health hazard. Wheat Triticum aestivum is a major global food crop. Cadmium, a toxic heavy metal, is a common environmental pollutant in agricultural soils. The present study was undertaken to systematically assess the toxicities of cadmium on T. aestivum. Besides, a feasibility study on using a white rot fungus Pleurotus pulmonarius in cleanup of artificially contaminated soils was carried out and assessed. In terms of acute phytotoxicity on seed germination and growth of germlings performed with a standardized bioassay, soil, in contrast to filter paper as matrix, showed sorption and reduced bioavailability which in turn, lowered the cadmium toxicity on T. aestivum. Moreover, genotoxicity in terms of DNA breakage measured by single cell gel electrophoresis was detected for cadmium (ranging from 1 to 50 mg/kg) after 3-day treatment. Root was the major organ for accumulating the pollutant but shoot suffered severe genotoxicities. Besides, differential expression of genes phytochelatin synthase (PCS) and metallothionein (MT) detected by reverse transcription polymerase chain reaction (RT-PCR) revealed that cadmium enhanced the expression of these genes in both filter paper and soil as matrices. Longer exposure, however, did not maintain the enhanced expression levels of PCS and MT. For chronic exposure up to the flowering and grain harvesting stages in pot plant system, tolerance towards cadmium was found; all seedlings survived at low contamination levels and up to 200 mg Cd/kg. The treated plants showed normal elongation rates but retarded growth at 2 and 4 months at extremely high concentrations of cadmium. At soil contamination levels exceeding the acceptable limits, cadmium (>1 mg/kg) retarded flowering development and reduced grain yield (seed mass). Grain nutrients, in terms of amino acid profile, protein content, dietary fibre content, mineral contents, carbohydrate content, were not affected by cadmium to great extents but genotoxicity was detected and the antioxidation bioactivity was decreased. Further, the harvested grains showed decreased viability as reflected by germination test to an extent in reverse proportions to the initial contaminated level of cadmium in soil for growing the plants. This reflects the inheritable damage to T. aestivum by soil cadmium. Cadmium was detected in grains harvested from contaminated soils at levels which exceeded the food safety standards (0.5 mg Cd/kg), indicating health hazards toward consumers. Thus environmental cleanup is urgently needed. A laboratory scale was set up to assess the bioremediation potential of a white rot fungus Pleurotus pulmonarius on contaminated soil for agricultural use. The fungus survived up to 162 mg Cd/kg after 5 weeks and fruiting of the fungus was inhibited by over 100 mg Cd/kg. Translocation of cadmium into the fungal fruiting bodies was observed, and the contents exceeded food safety standards. Although cadmium was extracted from soil and removed by translocation into the aerial fruiting bodies which could be removed, further investigation was needed to optimize the removal efficiency. When the treated soil was used as a matrix for germination of T. aestivum, both germination frequency and growth of germlings were similar to those in control soil. Thus the fungal treatment not just removed the soil contaminants cadmium but also ameliorate the toxicities of the soil contaminants. In face of the multiple toxicities exerted by the common soil contaminant cadmium on T. aestivum, more basic and applied work should be done to remediate agricultural land and to protect the land for crop production.

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