Arsenic in the Environment

1
Arsenic in the Environment

• Stephanie Ryder
• Department of Chemistry and Biochemistry
• Montana State University

2
Questions to Address

• What makes arsenic so toxic to humans and to the
  environment?
• What have microorganisms done to thrive in high
  arsenic concentrations? And what can we do with
  this data?

3
Dual Nature of Arsenic
Humans have known about arsenic for centuries and
it has been applied as a poison and a curative,
in metallurgy, for decoration and pigmentation,
in pyrotechnics and warfare

• Inorganic
• Arsenite
• Arsenate

• Organic
• Monomethylarsonic acid III and V
• Dimethylarsonic acid III and V

4
Arsenate and Arsenite

• Arsenate
• An analogue of phosphate and enters the cell
  through phosphate transporters
• Arsenate replaces phosphate in glycolysis that
  produces 1,3-BPG yielding 1-arseno-3-phosphoglycer
  ate, an unstable molecule that hydrolyzes to
  3-phosphoglycerate but no ATP is generated in
  this step.

• Arsenite
• Inhibits pyruvate dehydrogenase
• Readily absorbed by the digestive system and can
  be inhaled. Elimination at first is rapid by
  methylation and excretion but long term exposure
  is incorporated into bones, muscles, skin, hair
  and nails.

• Unlike organic pollutants, arsenic cannot be
  changed into non-toxic material waste rather it
  can be created into a less toxic form to living
  organisms in the environment.

5
The EPAs Standard

• In the U.S. the standard is set at 10µg/L or 10
  ppb

6
Toxic Effects of Arsenic
7
Effects of Arsenic Poisoning
8
Mono Lake, California

• Lab-based time course incubation experiments with
  Mono Lake water
• 0.25 mM arsenate was added and arsenate reduction
  was measured with 73As-arsenate.
• Determining the electron donors fueled in situ
  arsenate reduction, and the anions that could
  inhibit this process. This included attempts at
  using specific inhibitors of
  sulfate-reduction to help reveal the
  physiological types of microbes involved in
  arsenate reduction

9
Mono Lake, California

• Arsenite oxidation was discovered to be coupled
  to nitrate reduction
• Arsenate reduction is inhibited by nitrate
  reduction
• The rate of arsenite oxidation equaled the rate
  of arsenate reduction giving the appearance there
  was no loss of added arsenate.
• Dissolved organic carbon may fuel arsenate
  reduction
• High levels of sulfide, ammonia and methane that
  may serve as electron donors for arsenate
  reduction

10
Conclusions

• Places like Mono Lake have provided insight into
  microbial evolution and their diversity, arsenic
  metabolism and their biochemical reactions and
  the importance of such reactions to the
  biogeochemical cycles such as the sulfur,
  nitrogen and carbon cycles.
• Studies done in extreme environments can be
  transferred to the understanding of the
  hydrologic and geochemical systems of places like
  India and Bangladesh and address the concerns to
  human health.

11
Future Work

• An assay should be developed to quantify the
  rates of arsenate reduction and arsenite
  oxidation. A potential problem for this will be
  the adsorptive binding of iron III and phosphate
  which would compete with arsenate for binding
  sites.
• Ultimately, these techniques can be used on
  freshwater systems and drinking water aquifers.

12
Works Cited

• Naidu, R, Bhattacharya, P (2006). Management and
  remediation of arsenic from contaminated water.
  In. Managing Arsenic in the Environment From
  Soil to Human Health. 331354.
• Nriagu J (2002) Arsenic poisoning through the
  ages. In Frankenberger WT Jr (ed). Environmental
  Chemistry of Arsenic. Marcel Dekker, New York, pp
  1-26
• Quaghebeur, M, Rate, A, Rengel, Z, Hinz, C, 2005.
  Desorption Kinetics of Arsenate from Kaolinite as
  Influenced by pH. J. Environ. Qual. 2005 34
  479-486
• Oremland R.S., Stolz J.F., Hollibaugh J.T.
  (2004). The microbial arsenic cycle in Mono Lake,
  California. FEMS Microbiology Ecology, 48 1527