PMID: 12826480;PMCID: PMC1241557;Abstract:
Forty percent of hazardous waste sites in the United States are co-contaminated with organic and metal pollutants. Data from both aerobic and anaerobic systems demonstrate that biodegradation of the organic component can be reduced by metal toxicity. Metal bioavailability, determined primarily by medium composition/soil type and pH, governs the extent to which metals affect biodegradation. Failure to consider bioavailability rather than total metal likely accounts for much of the enormous variability among reports of inhibitory concentrations of metals. Metals appear to affect organic biodegradation through impacting both the physiology and ecology of organic degrading microorganisms. Recent approaches to increasing organic biodegradation in the presence of metals involve reduction of metal bioavailability and include the use of metal-resistant bacteria, treatment additives, and clay minerals. The addition of divalent cations and adjustment of pH are additional strategies currently under investigation.
Abstract:
The operation and exploitation of the Pilares breccia-pipe copper ore deposit and its subsequent cessation of activities in 1945 generated approximately 20 million tons in mine tailings and waste, currently covering a 19 hectares surface located within the urbanized area of Nacozari de Garcia, Sonora. The studied mine tailings are unconfined, with unstable slopes of 50°, lack of vegetation and seasonal efflorescent salts haved formed onthe surface. Such characteristics generate high eolian and water erosion and the possiblecollapse of material. In this work, calculated erosion is classified as severe to very severe. Granulometric characteristics of the tailings mark significant differences in theintensity of water erosion. The physical characterization of the tailings shows two areas of different granulometry that influence in the oxidation of sulfides and metal release: an area of large particle size, and another of fine particle size produced by the flotation process. Climate indexes were estimated for a time period from 1960 to 2011. The aridity index of Martonne shows a rank from 47 to 66, varying from humid in thé60s and́70s to perhumid in thé80s, and humid at present. The Lang index shows values from 15.2 to 22.8, which classifies as a steppe. Copper contents in residential soils and airborne dust collected at two meters height exceed the geochemical background.
PMID: 18409640;Abstract:
Eolian dispersion of mine tailings in arid and semiarid environments is an emerging global issue for which economical remediation alternatives are needed. Phytostabilization, the revegetation of these sites with native plants, is one such alternative. Revegetation often requires the addition of bulky amendments such as compost which greatly increases cost. We report the use of plant growth-promoting bacteria (PGPB) to enhance the revegetation of mine tailings and minimize the need for compost amendment. Twenty promising PGPB isolates were used as seed inoculants in a series of greenhouse studies to examine revegetation of an extremely acidic, high metal content tailings sample previously shown to require 15% compost amendment for normal plant growth. Several isolates significantly enhanced growth of two native species, quailbush and buffalo grass, in tailings. In this study, PGPB/compost outcomes were plant specific; for quailbush, PGPB were most effective in combination with 10% compost addition while for buffalo grass, PGPB enhanced growth in the complete absence of compost. Results indicate that selected PGPB can improve plant establishment and reduce the need for compost amendment. Further, PGPB activities necessary for aiding plant growth in mine tailings likely include tolerance to acidic pH and metals. © 2008 American Chemical Society.
Abstract:
Biodegradation rates for polycyclic aromatic hydrocarbons (PAH) in the environment are limited by their low solubility and sorption to solid surfaces. The purpose of this study was to quantify the effect of biosurfactants on the dissolution, bioavailability, and biodegradation of a slightly soluble PAH, phenanthrene, in a series of batch solution studies. A mathematical model that describes the combined effects of solubilization and biodegradation, including description of bioavailability within surfactant micelles, was used to analyze the experimental results. Two forms of the biosurfactant, a monorhamnolipid and a dirhamnolipid, were tested; it was found that both surfactants increased the solubility and enhanced the rate of phenanthrene biodegradation. Monorhamnolipid was more effective than dirhamnolipid for solubilization; however, overall rates of mineralization were essentially the same. This seems to result from variable bioavailability of substrate: phenanthrene within monorhamnolipid micelles was less bioavailable than phenanthrene within dirhamnolipid micelles. Therefore, the effect of a surfactant on biodegradation is s combination of the solubilizing power of the surfactant and the bioavailability of the substrate within the surfactant micelles. Model analysis of the solubilization data showed that the overall solubilization rate coefficient, K(L), increased with increasing biosurfactant concentration. Analysis of biodegradation data showed that enhanced biodegradation rates depend upon both K(L) and α, the coefficient for substrate bioavailability from micelles. Model simulations using parameters developed from test data are discussed.
