The existence and fate of heavy metals in soil is of concern not only because of their potential impact on microbial communities which comprise a """"""""healthy soil"""""""", but also because of the potential for groundwater contamination and hence, toxicological impact on human health. A major problem associated with remediating subsurface systems contaminated by heavy metals is the difficulty in delivering the metals to the surface for subsequent treatment. Typically, """"""""pump and treat"""""""" remediation does not attain cleanup within predicted timetables due to a """"""""tailing"""""""" effect once initial high heavy metal concentrations have been flushed out. Further complicating remediation of metal-contaminant sites is the fact that a large proportion of such sites are co-contaminated with organics. Such co-contaminated sites are increased stress on indigenous populations already impacted by organic contaminant stress. The Overall Hypothesis of this project is that microbially-produced sub-surfactants (biosurfactants) have the potential to reduce the tailing effect associated with """"""""pump and treat"""""""" and hence the amount of water pumped. Further, biosurfactants will act to mitigate metal toxicity to biodegrading microbes in co-contaminated sites allowing more rapid bioremediation. These two effects will allow significant monetary savings in operating costs both in terms of amount of water pumped and a shorter period of operation for the remediation system. These cost savings must be compared with the costs associated with the enhanced in situ treatment (i.e. cost of either in situ biosurfactant production, or ex situ (aboveground) biosurfactant production and injection). There are two principle aims of this research. The first is to demonstrate, at the field scale, the potential for enhanced removal of heavy metals from contaminated soils using biosurfactants. The second is to continue basic research in specific areas necessary to support transfer of this technology to the field scale. Specific objectives for the 5 year period are: Objective I -To demonstrate the effectiveness of biosurfactants as flushing agents for metal removal in contaminated soils. Objective II -To evaluate the potential for application of low levels of biosurfactant to mitigate metal toxicity in sites that are co- contaminated with metals and organics. Expected results Successful completion of the work proposed herein will result in several significant contributions. Some of the expected contributions include: 1. Demonstration of biosurfactant-enhanced metal. removal technology at the field scale 2. Demonstration of biosurfactant-induced protection against metal toxicity in co-contaminated sites at the intermediate-scale. 3. Information on the ability and selectivity of a variety of biosurfactants to bind metals. 4. Information on the ecology of biosurfactant producers, and in particular control of rhamnolipid biosynthesis and the potential for in-situ production of this biosurfactant.
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