Arsenic Cycling in the Environment
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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.

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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