Remediation of Metal-Contaminated Soil by Organic Metabolites from Fungi II—Metal Redistribution

Abstract

Exudation of low molecular weight organic acids by fungi was studied in a project focusing on bioremediation of metal-contaminated soils. The production of acids (mainly oxalic and citric acid) as a response to nutrient variations and presence of metals has recently been reported (Arwidsson et al. 2009). A significant release of metals was observed and was related not only to the production of organic acids but also to the resulting pH decrease in the systems. The processes governing the release and redistribution of metals in the soil-water fungus system were the focus of the present continuation of the project, based on observations of Aspergillus niger, Penicillium bilaiae, and a Penicillium sp. The release of lead was 12% from the soil with the second highest initial load (1,600 mg kg −1 ), while the release of copper was 90% from the same soil (140 mg kg −1 ). The dominating mechanism behind the release and subsequent redistribution was the change in pH, going from near neutral to values in the range 2.1-5.9, reflecting the production of organic acids. For some of the systems, the formation of soluble complexes is indicated (copper, at intermediate pH) which favors the metal release. Iron is assumed to play a key role since the amount of secondary iron in the soils is higher than the total load of secondary heavy metals. It can be assumed that most of the heavy metals are initially associated with iron-rich phases through adsorption or coprecipitation. These phases can be dissolved, or associated metals can be desorbed, by a decrease in pH. It would be feasible to further develop a process in technical scale for remediation of metalcontaminated soil, based on microbial metabolite production leading to formation of soluble metal complexes, notably with copper.

Identification of Scirpus triqueter root exudates and the effects of organic acids on desorption and bioavailability of pyrene and lead in co-contaminated wetland soils

“…As a complexing agent and a chelating agent, citric acid forms soluble complexes with the metals in the soil, constitutes an easily accessible carbon source for soil microorganisms, and further reduces the toxic effect of metals on plant (Arwidsson et al 2010). Stearic acid and myristic acid are mainly used as raw materials for production of surfactants.…”

Integration of microbial and chemical processing for a sustainable metallurgy

“…Therefore, the advantages of both processes in the hybrid mode can be taken into account for futuristic applications. Table represents several chemical, biological, and hybrid processing routes of metal resources . An analysis of Table reveals that by employing the hybrid process, recovery of metals can be significantly enhanced.…”

Soil Pollution in Dravyavati River and its Surrounding Areas of Jaipur City, Due to MSW (Municipal Solid Waste) and Industrial Waste

“…In modern economies, various types of activity, including agriculture, industry and transportation, produce a large amount of wastes and new types of pollutants in present scenario soil pollution has been continuously increasing as a result of industrial activities and contamination of soil constitutes a severe environmental problem all over the world. The Swedish Environmental Protection Agency estimates that there are about 83,000 contaminated areas in Sweden alone, many of them with mixed contaminants, i.e., both organic substances and metals [2,3] (SEPA 2007). Ivana etal [4] conducted a comprehensive study on Urban Soil Contamination by Potentially Risk Elements in Czech Republic, in Prague and Ostrava.…”