Abstract
This study aimed to clarify the magnitude of lead release from lead-sorbed animal manure compost (AMC) in rhizosphere soil compared with nonplanted soil of shooting range. The presence of buckwheat caused reduction in rhizosphere soil pH and enhancement in the level of water-soluble organic carbon compared with those of nonplanted soil. In addition, the presence of buckwheat altered the lead phases and increased the relative amount of the soluble exchangeable fraction, resulting in increase in the CaCl2-soluble lead level. In contrast, the presence of Guinea grass did not change the lead bioavailability or phases compared with nonplanted soil. Lead release tests in solution showed that between solution pH 5 and solution pH 7 the amount of lead released from the compost was higher in the rhizosphere soil of buckwheat than in nonplanted soil, whereas there was no significant difference between the rhizosphere soil of Guinea grass and nonplanted soil. These results suggest that the increase in the quantity of exchangeable lead resulting from the rhizosphere effect induces lead immobilized by the AMC to be remobilized. Therefore, AMC should be applied to soils that contain plants that are unable to alter the lead phases in the shooting range soil. Efforts should be particularly made to ensure that lead cannot be transformed to the exchangeable phase.
Highlights
In the soil of shooting ranges, lead derived from spent bullets typically accumulates at a very high concentration, causing heavy lead contamination in the soil
animal manure compost (AMC) should be applied to soils that contain plants that are unable to alter the lead phases present in the shooting range soil
The shoot height and dry weight of buckwheat grown in rhizosphere soil of shooting range with lead-immobilized compost did not significantly differ from that grown without compost, while the presence of lead suppressed the growth of Guinea grass
Summary
In the soil of shooting ranges, lead derived from spent bullets typically accumulates at a very high concentration, causing heavy lead contamination in the soil. A typical method of remediation of toxic-metal-contaminated soil is excavation and transport to landfill sites in Japan. Shooting ranges have an extensive area and a very low asset value due to their location away from residential areas. This method could not be applied due to its relatively high cost, which resulted in prohibiting entry into the shooting range. Chemical immobilization techniques represent a simple and eco-friendly approach for the prevention of toxic metal leaching from contaminated soils. Since the toxic metals are not removed from the soil following immobilization, remaining instead in the soil, better understanding of the immobilization mechanisms, that is, the formation of insoluble phases by the material and the subsequent dissolution of the toxic metals from the material following changes in soil parameters such as soil pH and oxic-redox conditions, is important to enhance the reliability of immobilization techniques [1]
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