2What is bioremediation? The use of bacteria and fungi and plants to break down or degrade toxic chemical compounds that have accumulated in the environment
3What are environmental contaminants? Pollutantsnaturally-occurring compounds in the environment that are present in unnaturally high concentrations.Examples:crude oilrefined oilphosphatesheavy metalsXenobioticschemically synthesized compounds that have never occurred in nature.Examples:pesticidesherbicidesplastics
4Early examples of bioremediation Outhouse→Centralized engineered wastewater treatment systemsMicroorganisms oxidize organic waste molecules to carbon dioxide and waterWhy do we want to use engineered man-made for this?
5More recent examplesBy 1970s it became apparent that we were polluting the environment faster than the natural microbial processes could degrade the pollutantsCongress established the Environmental Protection AgencyIdentified “Superfund Sites” that had priority over other polluted systems for special funding and cleanup in 19801 in 5 Americans lives within 3-4 miles of a polluted site treated by the EPANot much progress has been made even though $billions has been spent
6Groundwater contamination Groundwater constitutes 96% of available freshwater in U.S.95% of potable water in rural areas of U.S. comes from groundwaterIn 1988, EPA confirmed that 26 states had various amounts of 44 different pesticides in their groundwaterCost of cleanup is in the $ trillionsIssues that are still hotly debatedHow clean is clean?
8Most recentNational Institute of Environmental Health Sciences established the Environmental Genome ProjectStudy impact of environmental chemicals on human diseaseIdentify genes and their products that are sensitive to toxic chemicals in the environmentIdentify genes that encode for products that detoxify the chemicals
9What types of treatment technologies are in use to remove contaminants from the environment? Soil vapor extractionair spargingbioremediationthermal desorptionsoil washingchemical dehalogenationsoil extractionin situ soil flushing
10What Makes Bioremediation a Promising Approach? permanencecontaminant is degradedpotentially low cost60-90% less than other technologies
11Economics of in-situ vs. ex-situ remediation of contaminated soils Cost of treating contaminated soil in place $80-$100 per tonCost of excavating and trucking contaminated soil off for incineration is $400 per ton.Over 90% of the chemical substances classified as hazardous today can be biodegraded.
12Contaminants Potentially Amenable to Bioremediation ____________________________________________
13What challenges exist for bioremediation of pollutants and xenobiotics? may exist at high, toxic concentrationsdegradation may depend on another nutrient that is in limiting supplyXenobioticsmicrobes may not yet have evolved biochemical pathways to degrade compoundsmay require a consortium of microbial populations
14Fundamentals of cleanup reactions Aerobic metabolismMicrobes use O2 in their metabolism to degrade contaminantsAnaerobic metabolismMicrobes substitute another chemical for O2 to degrade contaminantsNitrate, iron, sulfate, carbon dioxide, uranium, technicium, perchlorate
17ATP Fe(III) CO2 Fe(II) Metabolism of a Pollutant-degrading Bacterium ACETATE*U(VI)*Co(III)*Cr(VI)*Se(VI)*Pb(II)*Tc(VII)*Benzoate*Toluene*Phenol*p-Cresol*BenzeneATPCO2Fe(II)*CCl4*Cl-ethenes*Cl-aromatics*Nitro-aromatics
18Uranium reduction leads to uranium precipitation and immobilization U6+solU4+insol
19Volatile organic compounds (VOC) These are major contributors to air pollutionPaint industryPharmaceutical industrybakeriesprintersdry cleanersauto body shops
20CometabolismBacterium uses some other carbon and energy source to partially degrade contaminant (organic aromatic ring compound)degradationproductscontaminantbacteriumcornstarchCO2 + H2O
21Hard to degrade contaminants Chlorinated hydrocarbonssolventslubricantsplasticizersinsulatorsherbicides and pesticides.
23Degradation of chlorinated hydrocarbons Degradation of organic toxins requires the participation of entire biochemical pathways involving many enzymes coded for by many genes.Some of the genes exist on the chromosome while other genes reside on plasmids.
24CO2 + H2OPhenol-degrading dmp operon is regulated by DmpR, a NtrC-like positive regulator.
25The layout of the genes involved in chlorocatechol-degradation on the plasmid is similar to the layout of the catechol-degrading genes on the chromosome
26Genetic engineering of bacteria to remove toxic metals from the environment E. coli bacteriumNew gene/transport proteinsHg2+-metallotheinHg2+→HgoHg2+New gene/enzymeHgo (less toxic form of metal)
27Phytoremediation ≈350 plant species naturally take up toxic materials Sunflowers used to remove radioactive cesium and strontium from Chrenobyl siteWater hyacinths used to remove arsenic from water supplies in Bangladesh, India
29Phytoremediation Drawbacks Only surface soil (root zone) can be treatedCleanup takes several years
30Transgenic plants Royal Demolition eXplosive Gene from bacterium moved toplant genomeStimulates plant growth!
31Careers in Bioremediation Outdoor inspectionLab testingAdministrationGovernmentEmployeeRegulatory oversightCompany employee
32SummaryMany factors control biodegradability of a contaminant in the environmentBefore attempting to employ bioremediation technology, one needs to conduct a thorough characterization of the environment where the contaminant exists, including the microbiology, geochemistry, mineralogy, geophysics, and hydrology of the system