1. 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
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
Arsenic Cycling in the Environment
Arsenic Removal
Experimental Setup
HACH BODTrak measured oxygen uptake in mg/L vs. time
Conducted at room temperature ( °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