Phytoremediation of Phytoremediation of ArsenicArsenicJoe Joe CharlsonCharlsonCE 421CE 421IntroductionIntroductionArsenic is listed as the #1 hazardous substance Arsenic is listed as the #1 hazardous substance according to the U.S. Agency for Toxic Substances according to the U.S. Agency for Toxic Substances and Disease Registryand Disease RegistryPicture of Arsenic mineral (source: Picture of Arsenic mineral (source: www.wikipedia.comwww.wikipedia.com, 2006), 2006)Arsenic BackgroundArsenic BackgroundSources of Arsenic contamination:Sources of Arsenic contamination:mine waste (primarily sulfide, iron and tin)mine waste (primarily sulfide, iron and tin)tanneries tanneries metal smelters metal smelters geothermal activitygeothermal activityArsenic has been used in the following:Arsenic has been used in the following:embalming fluidsembalming fluidspaint pigmentspaint pigmentsinsecticidesinsecticidesherbicidesherbicidesdefoliantsdefoliantsmetal alloysmetal alloysArsenic BackgroundArsenic BackgroundPoisonous effects of arsenic date back to 17Poisonous effects of arsenic date back to 17ththand 18and 18ththcenturies centuries when it was used to kill several kings, termed when it was used to kill several kings, termed ““Poison of kingsPoison of kings””Minnesota, Wisconsin, Michigan, North Dakota, and South Minnesota, Wisconsin, Michigan, North Dakota, and South Dakota have elevated amounts of arsenic in groundwaterDakota have elevated amounts of arsenic in groundwater10 ppb World Health Organization drinking water standard, 10 ppb World Health Organization drinking water standard, estimated that over 50 million people worldwide are drinking estimated that over 50 million people worldwide are drinking water with arsenic concentrations in excess of this standardwater with arsenic concentrations in excess of this standardHighly toxic due enzyme inhibition, is suspected as causal agentHighly toxic due enzyme inhibition, is suspected as causal agentin various forms of cancer and skin lesions in various forms of cancer and skin lesions Arsenic poisoning symptoms include severe stomach pain, Arsenic poisoning symptoms include severe stomach pain, nausea, headaches and usually leads to death if untreatednausea, headaches and usually leads to death if untreatedEffects of Arsenic Poisoning Effects of Arsenic Poisoning Skin lesionsSkin lesions(source: (source: www.soswww.sos--arsenic.netarsenic.net, 2006), 2006)Most Common Soil Arsenic SpeciesMost Common Soil Arsenic SpeciesArsenic is typically found in the soil in the Arsenic is typically found in the soil in the following forms: following forms: ArsentateArsentate, Arsenite, , Arsenite, dimethyldimethylarsenic acid and arsenic acid and monomethylmonomethylarsenic acidarsenic acidInorganic forms arsenate, or As (V), and Inorganic forms arsenate, or As (V), and arsenite, or As (III), most common in soilarsenite, or As (III), most common in soilArsenate prevails under aerobic Arsenate prevails under aerobic conditions, is less toxic and less mobile conditions, is less toxic and less mobile than arsenite, due to stronger soil sorptionthan arsenite, due to stronger soil sorptionCurrent Arsenic Remediation TechniquesCurrent Arsenic Remediation TechniquesSoil removalSoil removal--excavationexcavationCappingCapping--place hard cover over soilplace hard cover over soilSolidification and stabilizationSolidification and stabilization--inject polymers inject polymers and other stabilizing compounds into groundand other stabilizing compounds into groundAcidAcid--washing washing --Use aqueous acidic solution to Use aqueous acidic solution to extract waterextract water--soluble arsenicsoluble arsenicDisadvantages: $400,000 per hectacre, Disadvantages: $400,000 per hectacre, safety, some donsafety, some don’’t remove arsenict remove arsenicWhat is phytoremediation?What is phytoremediation?PhytoremediationPhytoremediation: The removal of a : The removal of a substance from the air, soil, or water via substance from the air, soil, or water via a microorganism or planta microorganism or plantSeveral subdivisions of Several subdivisions of phytoremediation: phytoremediation: phytovolatilizationphytovolatilization, , phytoextractionphytoextraction, , phytostabilizationphytostabilization, and , and rhizofiltrationrhizofiltrationWhy use phytoremediation?Why use phytoremediation?Low CostLow CostEnvironmentallyEnvironmentally--friendlyfriendlyMuch lower occupational riskMuch lower occupational riskArsenic is a chemical analog to Arsenic is a chemical analog to phosphorus (i.e. itphosphorus (i.e. it’’s easily taken up by s easily taken up by plants)plants)Why is arsenic toxic for most Why is arsenic toxic for most plants?plants?Arsenic toxicity threshold for most plants is Arsenic toxicity threshold for most plants is (40(40--200) mg As per kg DW depending on soil 200) mg As per kg DW depending on soil conditionsconditionsArsenate replaces phosphate when taken up, and Arsenate replaces phosphate when taken up, and disrupts production of ATP, which results in cell disrupts production of ATP, which results in cell deathdeathArsenic is inhibitory towards cell function because it Arsenic is inhibitory towards cell function because it reacts with sulfydryl enzymes and disrupts their reacts with sulfydryl enzymes and disrupts their activityactivityArsenic Accumulating PlantsArsenic Accumulating PlantsPteris Pteris fernsfernsPityrogrammaPityrogrammacalomelanoscalomelanosLemna Lemna gibbagibba(duckweed)(duckweed)LepidiumLepidiumsativumsativum(watercress)(watercress)LupinusLupinusalbusalbus(white (white lupinlupin))Mustard Plants Mustard Plants Pteris vittataPteris vittataFactors affecting arsenic Factors affecting arsenic accumulationaccumulationArsenic sorption to soil is the primary process that Arsenic sorption to soil is the primary process that immobilizations this metal, depends on soil pH, immobilizations this metal, depends on soil pH, amount of organic matter, and textureamount of organic matter, and textureSoil pH: Arsenate absorbed to soil (4Soil pH: Arsenate absorbed to soil (4--7), 7), Arsenite (7Arsenite (7--10)10)Presence of Ferric and Aluminum arsenic