Microbial Uptake of Arsenic

1. Arsenic Cycling in the Environment • Oxidation and reduction reactions occur in sediment • Anthropogenic and natural emissions • Methylation processes by algae in surface waters • As is consumed by certain organisms in the water Microbial Uptake of Arsenic Background Lara Derchak - Civil Engineering Erin Frey - Chemical Engineering Crystal L. Mattson – Civil Engineering • Toxicity • Arsenic is extremely toxic causing severe health problems • LD50 of arsenic is between 15 and 30 mg/kg of body weight • In comparison, NaCl is 3,000 mg/kg body weight and nicotine is 60 mg/kg body weight • Exposure • Dermal Contact • Ingestion • Inhalation • Health Effects • Immediate symptoms: vomiting, esophageal & abdominal pain and bloody diarrhea • Long term exposure: cancer, gangrene, loss of feeling in limbs, hearing impairment, diabetes, heart and circulatory problems, and affects the gastrointestinal system and liver Project Objectives Oxygen Uptake Results • Determine if a mixed bacteria culture is a viable treatment option • Study the adsorption of arsenic by iron • Identify algae species that will uptake arsenic and study the impact on growth Mixed Bacteria Culture • Obtained bacteria from a local wastewater treatment plant • Exposed bacteria to varying concentrations of arsenate (Na2HAsO4) and arsenite (NaAsO2) (0.05 mg/L – 1.5 mg/L) • Second experiment had concentrations varying from 50 mg/L to 1600 mg/L. • Glucose (C6H12O6)used as the carbon source Arsenic Removal Experimental Setup • HACH BODTrak measured oxygen uptake in mg/L vs. time • Conducted at room temperature (22 + 0.5°C) • Arsenic concentrations measured at conclusion of experiment using HACH Arsenic Test Kits Conclusions Drinking Water Regulations Algae • USEPA Standard: 0.01 mg/L • WHO Standard: 0.01 mg/L • > 0.05 mg/L (50 ppb) As concentrations found throughout country • Large populations exposed to As because of groundwater contamination worldwide • As contaminated countries include Bangladesh, Australia, Chile, and New Zealand • MIXED CULTURE • At low concentrations, significant amounts of both forms of arsenic were removed (60% average) • It is apparent that low concentrations of arsenic may be removed by aerobic bacteria • At high concentrations, varying removal was noted for both forms • Arsenite removal 48% • Arsenate removal 77% • Probable cause for low arsenite removal is toxicity • Probable mechanism for removal is biosorption • Higher concentrations significantly impacted growth • Inhibition is approximately 50% at 1600 mg/L contradicting available literature • ALGAE • Removal of arsenic was time dependent with major removals occurring within the first hour of experimentation. • Desorption of arsenic was evident after the first hour. • Algae morphology was impacted by the presence of arsenic. However the impact was not arsenic concentration dependent. • Algal morphology changed to clumping at higher concentrations of arsenic. • Significant differences were not noticed for arsenic uptake with the two types of algae. Use of microorganisms for arsenic removal from water may be a viable mechanism of arsenic removal. • Two methods by which algae can uptake heavy metals • Biosorption • Bioaccumulation • Scenedesmus abundans and Chlorella vulgaris are both common green freshwater algae capable of metal uptake • Batch experiments with algae and varying concentrations of arsenic were conducted. • Arsenic concentrations were measured with time. • Algae morphology was checked at end of experiments. Bangladesh • People used the rivers as their source of water • Began to get sick and even die because of the bacterial contamination • The solution: Change to groundwater • Did not realize the arsenic problem at the time • Groundwater arsenic contamination was first discovered in 1993 • Thousands of wells were already in place • 5 times higher than the world standard Oxygen Uptake Results Acknowledgements Dr. Kauser Jahan Dr. Patricia Mosto Costantinos Tsoukalis