dc.description.abstract | Many species of heavy metals released from anthropogenic activities are highly mobile in the environment, thereby posing a potential threat to human health and wildlife reproduction. Soil contamination with heavy metals is of particular concern, as the pollutants may reach concentrations that are directly toxic to plants/crops and microorganisms. Moreover, contaminated soil may act as a constant pollution source where runoff and leachate from soil matrix may lead to elevated levels of heavy metals in surface and groundwater environments, causing a great risk for safe water supplies. Therefore, a considerable amount of work has been carried out to address the remedies that may efficiently control or cleanup the contaminated sites. However, unlike organic pollutants, metals cannot be degraded and thus their chemical characteristics significantly limit the application of many remediation techniques. Nonetheless, according to the U.S. EPA, solidification/stabilization is one of the best demonstrated available technologies to treat certain industrial wastes and contaminated soil. In this study, stabilization of lead, chromium, and cadmium in soil with three types of biopolymers, including alginate, xanthan and guar gum, was demonstrated and evaluated. The reason for biopolymers being selected was because they have high affinity for binding heavy metals and have been considered as renewable and cost-effective materials. These materials can also potentially be used as barriers to prevent the migration of hazardous waste, which requires slow or non-biodegradability in order to permanently immobilize the pollutants in soil. Indeed, using borax and alkaline earth metal ions such as calcium and barium ions as crosslinking agents, the biodegradability of crosslinked biopolymers used in this study was significantly decreased presumably due to the formation of interpenetrating polymer networks (IPNs), which are able to make the crosslinked products persistent in the environment. The results of weight swelling ratio, an indication for the extent of crosslinking of the IPNs, also supported the presence of complex polymer structures in terms of the high crosslinking density and the low water content. When this crosslinked biopolymer technology was applied to synthetic polluted soil of lead, chromium and cadmium to create an in situ system that acted as cages for trapping these metals in soil, remarkable results were obtained: under the optimum conditions, up to 81% of lead was successfully immobilized in soil using guar crosslinked by borax, and 85% of cadmium was stabilized with xanthan and guar crosslinked by borax. These results show that the soil treatment with crosslinked biopolymer networks to stabilize lead, chromium and cadmium was effective. The unique property of the networks to be resistant to biodegradation may add another value to this technology, providing a promising means to permanently stabilize heavy metals in soil. | en_US |