This project identifies the crucial issues of the administration and remediation for the farm land contaminated with heavy metals, and aims at proposing the applicable amendment to the current administrative measures. With comprehensive information collected, including (1) committee meeting minutes of the Soil and Groundwater Pollution Remediation Fund Management Board, (2) the consultation results with the professionals, and (3) the suggestions from the farmers, therefore, this project evaluates several critical issues around the administrative measures and remediation technologies.
Since the fact that cadmium pose severe risk on crop hygiene and affected by several factors including soil characteristic, the quality of irrigation water, the variety of rice cultivar, and agricultural water management. Accordingly, the project implements the investigation to clarify dominant factor and selects representative farmland targets. After systematic investigation and results evaluation, aerobic soil water regime might be attributed to elevation of the cadmium concentration in the rice tissue, which might be affected by drainage quality of the site, availability of irrigation water and the manner of agricultural water management. Hence the project proposed two measures to mitigate the crop contamination by cadmium, including (1) conduct agricultural management and (2) permit specific crop cultivation.
By collecting and reviewing both domestic and abroad ordinances and management strategies of farmland remediation, two popular strategies served as main trends are listed as follow, (1) remove the contamination from soil, and (2) in-situ stabilization of heavy metal in the soil to reduce the hazardous risk. Considering the availability of technology for domestic use, the project proposes the promising agricultural management technologies. Afterwards, the field experiment is conducted on the Cu, Zn, Cr and Ni contaminated site to evaluate the performance of the strategies. The results are listed as following:
1. Soil pH was significantly raised after lime and oyster shell application, and the availability of copper, zinc, and nickel was reduced remarkably. Thus, adopting alkaline material such as lime is identified as a potential agricultural management to mitigate contamination. Benefit of heavy metals stabilization in soil might be achieved when green manure was mutually composted.
2. The contaminants concentration in the rice tissue is related to the translocation mechanism of paddy rice. Upper limit of heavy metal concentration in the rice tissue is observed, and which won’t be elevated with soil concentration. Most contaminants concentrated in the rice root, while the concentration of heavy metal in the brown rice was found as follow, Cu concentration was lower than 10 mg/kg, Zn concentration was lower than 30 mg/kg, Ni concentration was lower than 15 mg/kg, and Cr concentration was lower than 1 mg/kg, which was similar to historical records. Therefore, the project recognizes the safety of the rice and is not affected by soil contaminant.
3. No toxic appearance on the rice plant was observed during the growing period in the experiment. Furthermore, the rice yield and quality was also not affected by the soil contaminants, when the Cu concentration in the soil was not higher than 700 mg/kg.
Around the world, applied biochar to stabilize heavy metals in soil and phytoextraction extraction are two promising technologies among contaminated soil remediation. The project evaluates the remediation potential by conducting pot experiments.
1. Two commercial biochars are tested, while Availability of heavy metals in the soil and the metal concentration in the crop tissues are two main factors to evaluate the experiment result. Results show that the benefit of biochr amendment is not prominent, since the material are unable to adsorb the heavy metals thus decrease the available concentration in soil and plant tissue. Reason inferred might be related to poor affinity between the heavy metals and the functional groups, which attributed to the impropriate pyrolysis process of the biochar.
2. Four plant species are inoculated with arbuscular mycorrhizal fungi (AMF) to evaluate the effect of phytoextraction. Including Helianthus annuus, Zea mays and two species of Impatiens walleriana are tested. The biomass of the plant is significantly increased by AMF inoculation, while the uptake amount of Cu, Zn, Cr and Ni annul per ha are 0.2-4.5 g, 2.0-37 g, lower than 0.15 g, and 1.3-8.8 g, respectively. Considering the long-term administrative control and the interest loss of farmers, phytoremediation cannot serves as a single approach to reduce soil metal concentration and meet the regulation standard. To strengthen the remediation effect, domestic agronomic crops with developed cropping system will be a promising candidate.
Soil is more than the natural resource, but the precious properties of every human generation. The project emphasized the necessity to regard the contaminated soil as a resource. Differentiate the soil contaminants by their toxic characteristic and consider correspondent remediate measurements. For the site contaminated with Cu, Zn, Cr and Ni, green and sustainable remediation methods are advised and should follow with comprehensive risk assessment. The project considers the agricultural environment as a whole, introduces the “Blueprint of Remediation and Management Strategies for Farmland Contaminated with Heavy Metals” as the reference for the authority to develop the policies and technologies for the farmland contaminated with heavy metals, after analyzing the obstacles in current administrative management, reviewing the management strategies and remediation technologies both domestic and abroad, as well as considering the operation mechanism of the Soil and Groundwater Pollution Remediation Fund Management Board.
