Water Lecture 6

Inorganic Arsenic

Known carcinogen linked to various cancers.

Chronic Exposure Effects

Causes respiratory, cardiovascular, and kidney diseases.

EPA MCL

Maximum contaminant level set at 10 μg/L.

Sources of Arsenic

Occurs naturally in sediments and rocks.

Hardrock Mining

Contributes to arsenic contamination in water.

Community Water Systems

Over 50% detected arsenic in U.S. CWSs.

MCLG for Arsenic

EPA's goal is 0 μg/L, no safe level.

Epidemiologic Evidence

Current MCL insufficient for health protection.

Arsenic in Bangladesh

High contamination from shallow groundwater wells.

Visual Indicator of Redox State

Sand color indicates oxidation-reduction conditions.

Orange Sands

Indicate presence of Fe(III) oxides, lower arsenic.

Gray Sands

Associated with higher dissolved arsenic concentrations.

Spatial Heterogeneity

Redox conditions vary over short distances.

Practical Application of Sand Color

Guides drillers to low-arsenic groundwater.

Arsenic Source

Originates from Himalayan sediments and erosion.

Microbial Reduction

Destabilizes Fe(III) oxides, releasing arsenic.

Organic Carbon Role

Decomposition fuels microbial reduction of arsenic.

Biogeochemical Transformations

Control arsenic levels in groundwater.

Sulfide Minerals

Contain arsenic, oxidize to release it.

Oxidation Process

Pyrite oxidation releases arsenic and iron oxides.

Arsenic Behavior

Soluble in oxidizing conditions, more toxic.

Reduction of Arsenic

Changes arsenic to less soluble forms.

Iron Oxides Formation

Traps arsenic in floodplains and riverbeds.

Arsenic Trapping

Occurs in iron oxide particles in floodplains.

Health Risks

Contaminated water poses significant health threats.

Groundwater Contamination

Arsenic levels influenced by geological processes.

Metabolic By-products

Correlate with high groundwater arsenic levels.

Contaminated Water Delay

Health effects appear after 10 years of exposure.