Arsenic

Arsenic (As)

Pollutant Information

Chemical Formula:	As (various oxidation states)
Pollutant Family:	Heavy metals/Metalloids
CAS Number:	7440-38-2
Atomic Weight:	74.92 g/mol
Solubility:	Variable by species
Persistence:	Non-biodegradable, persistent
Regulatory Status:	WHO/EPA Class 1 carcinogen

Overview

Arsenic is a naturally occurring metalloid and one of the most toxic elements known to humans. While naturally present in Earth's crust, widespread contamination from industrial activities, mining, and agricultural practices has made arsenic contamination a global environmental and public health crisis. Over 100 countries are affected by arsenic contamination, with groundwater contamination being particularly problematic as it affects drinking water sources for millions of people worldwide. Arsenic exists in multiple chemical forms with varying toxicity levels, making understanding its environmental behavior crucial for effective remediation.

Characteristics

Physical Properties

• State at room temperature: Solid (metallic gray)
• Color/Appearance: Gray metallic in pure form; compounds vary
• Odor: Odorless in inorganic forms
• Melting point: 817°C (sublimes without melting)
• Boiling point: 614°C (sublimation point)
• Density: 5.73 g/cm³

Chemical Properties

• Oxidation states: -3, 0, +3, +5 (arsenite As(III) and arsenate As(V) most common)
• pH effects: As(III) more mobile and toxic at neutral pH; As(V) more stable
• Reactivity: Forms complexes with sulfur compounds, readily binds to iron oxides
• Stability: Persistent in environment, undergoes redox transformations
• Bioavailability: As(III) more bioavailable and toxic than As(V)

Environmental Behavior

• Mobility in soil: Highly variable; As(III) more mobile than As(V)
• Water solubility: As(III) and As(V) both soluble; varies with pH and redox conditions
• Volatility: Some methylated forms can volatilize
• Adsorption: Strongly adsorbs to iron/aluminum oxides, clay minerals
• Half-life: Persistent - does not degrade, only transforms between species

Sources & Contamination Pathways

Industrial Sources

• Mining and smelting operations (copper, lead, zinc, gold)
• Coal combustion and power generation
• Wood preservative industry (chromated copper arsenate - CCA)
• Glass and electronics manufacturing
• Pesticide and herbicide production

Agricultural Sources

• Historical use of arsenic-based pesticides and herbicides
• Contaminated irrigation water
• Phosphate fertilizers containing arsenic impurities
• Poultry litter from arsenic-containing feed additives

Urban/Residential Sources

• CCA-treated lumber in playgrounds, decks, and structures
• Contaminated soil around treated wood structures
• Old paint containing arsenic compounds
• Legacy contamination from historical industrial activities

Natural Sources

• Weathering of arsenic-bearing rocks and minerals
• Volcanic emissions and geothermal activity
• Natural groundwater contamination in sedimentary aquifers
• Marine sediments and seafloor deposits

Environmental & Health Impacts

Effects on Land/Soil

• Soil chemistry: Alters soil pH, competes with phosphate for binding sites
• Soil biology: Toxic to soil microorganisms, reduces microbial diversity
• Plant uptake: Readily absorbed by plants, especially rice in flooded conditions
• Groundwater contamination: Leaches into aquifers, especially under reducing conditions
• Ecosystem disruption: Bioaccumulates in food webs, affects plant and animal health

Effects on Water Systems

• Aquatic toxicity: Toxic to fish, algae, and aquatic invertebrates
• Bioaccumulation: Accumulates in aquatic organisms, particularly in organs
• Water quality: Renders water unsafe for drinking, irrigation, and aquaculture
• Redox cycling: Environmental conditions affect arsenic mobility and toxicity

Human Health Effects

Acute Exposure

• Gastrointestinal distress (nausea, vomiting, diarrhea)
• Cardiovascular shock and organ failure (severe cases)
• Neurological symptoms (confusion, seizures)

Chronic Exposure

• Skin lesions, hyperpigmentation, and keratosis
• Multiple cancers (skin, lung, bladder, kidney, liver)
• Cardiovascular disease and diabetes
• Neurological effects and developmental disorders
• Arsenicosis - chronic arsenic poisoning syndrome

Vulnerable Populations

• Children: Developmental impacts, reduced IQ, growth retardation
• Pregnant women: Increased risk of birth defects, low birth weight
• Rural communities: Dependent on contaminated groundwater for drinking
• Agricultural workers: Exposure through contaminated soil and irrigation water
• Mining communities: High exposure from industrial activities

Detection & Testing

Sampling Methods

• Water sampling: Filtered and unfiltered samples to distinguish dissolved vs. particulate arsenic
• Soil sampling: Grid sampling, attention to redox conditions and pH
• Biological sampling: Plant tissue, especially roots and shoots for bioaccumulation
• Sediment sampling: Core samples from contaminated water bodies

Analytical Methods

• ICP-MS (Inductively Coupled Plasma Mass Spectrometry) - Detection limit ~0.1 μg/L
• Hydride Generation-Atomic Fluorescence Spectroscopy (HG-AFS)
• Ion chromatography for arsenic speciation (As(III) vs As(V))
• Field test kits - Semi-quantitative, good for rapid screening

Regulatory Limits

• WHO drinking water guideline: 10 μg/L
• EPA drinking water standard: 10 μg/L (Maximum Contaminant Level)
• EPA soil screening level: 0.39 mg/kg (residential)
• Agricultural soil limits: Vary by country, typically 20-40 mg/kg

Bioremediation Organisms

Bacteria

• Delftia spp. - Arsenite oxidation, groundwater bioremediation applications
• Sphingomonas desiccabilis - ArsM gene expression, volatile arsenic production
• Bacillus subtilis and B. idriensis - Arsenic biotransformation and detoxification
• Exiguobacterium profundum - Arsenic biosorption and biotransformation
• Stenotrophomonas spp. - Multiple arsenic resistance mechanisms
• Pseudomonas spp. - Arsenic oxidation and biosorption

Fungi

• Aspergillus spp. - Most studied for arsenic bioremediation, soil application
• Westerdykella aurantiaca - Arsenic methyltransferase (WaarsM gene), volatilization
• Piriformospora indica - Endophytic fungus, reduces arsenic availability to plants
• Trichoderma spp. - Soil bioaugmentation, plant growth promotion
• Saccharomyces cerevisiae - Model organism, engineered strains for bioremediation

Plants (Phytoremediation)

• Pteris vittata (Chinese brake fern) - First identified arsenic hyperaccumulator, up to 2.3% As in fronds
• Pityrogramma calomelanos - Silver fern, arsenic hyperaccumulator
• Indian mustard (Brassica juncea) - Arsenic accumulator, enhanced with amendments
• Sunflower (Helianthus annuus) - Moderate accumulator, high biomass production
• Hybrid poplar - Phytostabilization and limited phytoextraction
• Rice (Oryza sativa) - Modified varieties for reduced arsenic uptake in grains

Other Organisms

• Microalgae (Chlorella vulgaris) - Biosorption for water treatment
• Macroalgae (Colpomenia sinuosa) - Marine arsenic biosorption
• Arbuscular mycorrhizal fungi - Enhance plant arsenic uptake and tolerance
• Engineered organisms - Genetically modified bacteria and plants with enhanced capabilities

Bioremediation Strategies

Phytoextraction with Hyperaccumulators

• Chinese brake fern cultivation: Multiple harvests, phosphate amendment enhancement
• Mycorrhizal enhancement: Arbuscular mycorrhizal fungi increase arsenic uptake
• Soil amendment strategies: Phosphate additions mobilize soil arsenic for plant uptake
• Hydroponic systems: Large-scale groundwater treatment using P. vittata

Microbial Bioremediation

• Bioaugmentation: Introducing arsenic-resistant bacteria to contaminated sites
• Constructed wetlands: Engineered systems with arsenic-transforming microorganisms
• Bioreactors: Controlled microbial systems for water treatment
• In-situ biostimulation: Enhancing native microbial arsenic transformation

Integrated Phytobial Approaches

• Plant-microbe partnerships: Combining hyperaccumulator plants with beneficial microorganisms
• Rhizosphere enhancement: Plant growth promoting bacteria with arsenic tolerance
• Transgenic approaches: Genetically modified plants expressing microbial arsenic genes

Alternative Treatment Methods

Physical Treatment

• Coagulation-flocculation: Iron/aluminum salts for arsenic precipitation
• Adsorption: Activated alumina, iron-based adsorbents
• Membrane filtration: Reverse osmosis, nanofiltration
• Ion exchange: Selective resins for arsenic removal

Chemical Treatment

• Oxidation: Convert As(III) to As(V) for easier removal
• Precipitation: Lime treatment for arsenic precipitation
• Soil stabilization: Iron amendments to immobilize arsenic
• Electrochemical treatment: Electrocoagulation and electroflocculation

Disposal Methods

• Secure landfill: Hazardous waste disposal for concentrated arsenic waste
• Vitrification: High-temperature treatment to create stable glass matrix
• Arsenic recovery: Industrial recycling of arsenic-containing materials
• Biomass disposal: Safe disposal of arsenic-laden plant material after phytoextraction

Case Studies

Large-Scale Hydroponic Arsenic Remediation - Florida, USA

• Location: Contaminated groundwater site, Florida
• Contamination source: Industrial legacy contamination
• Treatment method: Hydroponic system with Chinese brake fern
• Organisms used: Pteris vittata (Chinese brake fern)
• Duration: 30-week study with multiple cycles
• Results: Reduced arsenic from 140-180 μg/L to <10 μg/L in 6-8 weeks
• Innovation: 600L tanks with 32 ferns each, optimized harvesting regimes
• Source: Natarajan et al., Environmental Science & Technology

Mycorrhizal-Enhanced Phytoremediation Study

• Location: Greenhouse study with field application
• Contamination source: Artificially spiked soils (50-100 mg/kg As)
• Treatment method: Chinese brake fern with arbuscular mycorrhizal fungi
• Organisms used: P. vittata + AM fungi community from As-contaminated site
• Duration: Multiple growing seasons
• Results: AM fungi increased arsenic uptake and plant biomass at high As levels
• Innovation: Demonstrated symbiotic relationship enhances phytoremediation efficiency
• Source: Leung et al., Environmental Pollution, 2006

Transgenic Arsenic Volatilization - Laboratory to Field

• Location: Laboratory and controlled field trials
• Contamination source: Various arsenic-contaminated soils
• Treatment method: Genetically modified organisms expressing arsM gene
• Organisms used: Transgenic rice, Arabidopsis with WaarsM gene from Westerdykella aurantiaca
• Duration: Multiple growing seasons
• Results: 10-fold increase in volatile arsenic production, reduced grain accumulation
• Innovation: Genetic engineering approach for arsenic volatilization
• Source: Multiple studies in Biotechnology Advances review, 2023

Prevention Strategies

Source Reduction

• Elimination of arsenic-based pesticides and wood preservatives
• Improved mining and smelting practices with better waste management
• Alternative materials for wood preservation and industrial applications
• Cleaner coal technologies and emission controls

Best Management Practices

• Proper disposal of CCA-treated lumber and arsenic-containing materials
• Groundwater monitoring in arsenic-prone geological areas
• Agricultural water quality testing and management
• Soil testing before residential development in industrial areas
• Rice cultivation practices to minimize arsenic uptake

Groups & Projects Working on This Pollutant

• University of Florida - Soil and Water Sciences - Lena Ma Lab - Chinese brake fern research, phytoremediation optimization
• Chinese Academy of Sciences - Plant Cell Engineering Lab - Molecular mechanisms of arsenic hyperaccumulation
• UNICEF - Arsenic Mitigation Programs - Community water systems, Bangladesh and India
• WHO Global Health Observatory - Arsenic monitoring - International health surveillance and guidelines
• Superfund Research Centers - Multiple US Universities - Contaminated site remediation research
• International Association of Hydrogeologists - Arsenic Working Group - Groundwater contamination research
• Asian Development Bank - Arsenic contamination projects - Rural water supply solutions across Asia

Resources

Scientific Literature

• Ma et al. (2001). "A fern that hyperaccumulates arsenic." Nature 409:579
• Zhao et al. (2009). "The Arsenic Hyperaccumulator Fern Pteris vittata L." Environmental Science & Technology
• Rathinasabapathi et al. (2023). "Biotechnology Advances in Bioremediation of Arsenic: A Review." Toxics

Government Resources

• EPA Arsenic Information and Regulations
• WHO Arsenic in Drinking Water Fact Sheet
• USGS National Arsenic Occurrence Database
• CDC Arsenic Health Effects and Exposure Information

Testing & Analysis

• Environmental testing laboratories - ICP-MS analysis - Contact state environmental agencies
• Home test kits - Semi-quantitative arsenic detection - Hardware stores and online
• University extension services - Soil and water testing programs
• Certified laboratories - EPA-approved methods for regulatory compliance

Related Pollutants

• Lead - Often co-occurs in mining waste and industrial contamination
• Cadmium - Similar environmental behavior and health effects
• Mercury - Heavy metal with similar bioaccumulation patterns
• Chromium - Co-contaminant in CCA-treated wood sites
• Copper - Present in CCA formulations and mining waste
• Selenium - Similar metalloid properties and plant accumulation patterns

Last updated: June 24, 2025
Page maintainer: Bioremmy