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Name: Selenious acid
Chemical Formula: H2SeO3
Synonyms: Selenious acid, selenium dioxide solution
Appearance: Clear, colorless to slightly yellowish liquid
Common Uses: Serves in glass manufacturing, textile mordanting, lab reagents, production of selenates, and chemical synthesis
GHS Classification: Acute toxicity (oral, dermal, inhalation), severe skin burns, serious eye damage, hazardous to aquatic life
Main Hazards: Toxic if swallowed, inhaled, or absorbed through skin. Causes severe skin burns and eye damage. Environmental persistence poses a risk for aquatic organisms.
Pictograms: Corrosive, Toxic, Environmental hazard (in jurisdictions adopting GHS)
Signal Word: Danger
Notable Symptoms: Shortness of breath, nausea, vomiting, skin irritation, eye pain and damage, kidney or liver trouble with repeated exposure
Chemical: Selenious acid
CAS Number: 7783-00-8
Concentration: Usually supplied as varying concentrations of aqueous solution, content by percent always dictates risk
Impurities: Trace amounts of selenium dioxide can occur, depending on synthesis route
Inhalation: Move person to fresh air, keep them calm, seek immediate medical attention
Skin Contact: Remove contaminated clothing, rinse affected skin areas carefully with plenty of running water for at least 15 minutes, call a physician
Eye Contact: Flush with running water for at least 15 minutes while lifting eyelids, get urgent medical help
Ingestion: Never induce vomiting, rinse mouth with water, seek medical advice promptly, offer water to drink if conscious
Additional Notes: Rescuers should wear gloves and avoid direct contact, be mindful of personal safety
Suitable Extinguishing Media: Water spray, dry chemical, carbon dioxide, foam
Special Hazards: On heating or in contact with very reactive chemicals, may decompose to release toxic selenium fumes and oxides
Protective Equipment: Firefighters need self-contained breathing apparatus, fully protective clothing
Hazardous Combustion Products: Selenium oxides, dangerous gases
General Advice: Move unaffected material away from immediate fire area if safe to do so, avoid runoff into waterways
Personal Precautions: Avoid skin and eye contact, wear gloves, safety goggles, chemical-resistant clothing, and if needed, suitable respiratory protection
Environmental Precautions: Prevent liquid and solutions from entering sewers, drains, or natural waters, contain spillage, alert authorities if substantive release occurs
Spill Cleanup: Neutralize area with sodium carbonate or bicarbonate, absorb with inert material (such as dry sand), scoop up and place in a suitable, labeled waste container
Decontamination: Rinse affected surfaces with large amounts of water after cleanup
Handling: Minimize dust or mist formation. Use only in well-ventilated areas with proper chemical-resistant gloves, lab coat, and eye/face protection. Never eat, drink, or smoke in areas with active use. Practice thorough hand washing after each use.
Storage: Keep container tightly closed in a dry, ventilated, locked cabinet away from incompatible substances, notably reducing agents and strong bases. Prevent corrosion of storage materials. Avoid exposure to direct sunlight and temperature extremes.
Exposure Limits: Occupational exposure limit for selenium compounds (as Se) varies by jurisdiction, often around 0.2 mg/m3 for an 8-hour time-weighted average
Engineering Controls: Local exhaust ventilation, fume hood for lab use, catch basin for storage and handling
Personal Protective Equipment: Gloves (nitrile, neoprene), chemical-resistant apron, safety goggles or face shield, NIOSH-approved respirator where fumes, dust, or aerosols occur
Hygiene: Change work clothes after handling, avoid direct contact with skin, eyes, or clothing, wash hands thoroughly before breaks and at end of work shift
State: Liquid (in solution), can occur as white crystalline solid
Odor: Nearly odorless
Solubility: Fully soluble in water
Melting Point: 70 °C (for pure compound, rare outside specialty labs)
Boiling Point: Decomposes before boiling
pH: Acidic, usually below 2 for concentrated solution
Vapor Pressure: Low at room temperature
Density: About 2.4 g/cm3 for pure compound, lower in solution
Stability: Remains stable in properly sealed container, away from light and excessive heat
Conditions to Avoid: High temperatures, direct sunlight, incompatibility with strong reducing agents, organic solvents, and strong bases
Decomposition Products: Selenium oxides, which can be toxic by inhalation
Incompatible Materials: Strong reducing agents, combustible materials, alkalis, metals in powder form
Polymerization: No hazardous polymerization reported, though violent reactions possible with selected reagents
Acute Toxicity: Toxic at low doses. LD50 values for oral exposure in rats ranging around 7 mg/kg bodyweight
Routes of Exposure: Inhalation, ingestion, skin/eye contact pose significant risks
Symptoms: Severe gastrointestinal irritation, nausea, vomiting, headache, dizziness, possible lung damage, destruction of red blood cells with chronic exposure
Chronic Effects: Kidney and liver damage, selenium buildup, garlic breath odor, peripheral nervous system effects
Carcinogenicity: Unclear classification, but chronic overexposure raises concern; some agencies call for precaution
Aquatic Toxicity: Harms fish and aquatic invertebrates even at very low concentrations
Persistence and Degradability: Selenium persists in aquatic systems, toxic effects may last over time
Bioaccumulation: Potential for selenium bioaccumulation in aquatic organisms and food chains is well documented
Special Risks: Small quantities can poison whole water systems, risk rises when improperly managed
Safe Disposal: Treat as hazardous chemical waste, assign to solvent waste drums or chemical waste containers only
Disposal Method: Chemical incineration or handling by licensed hazardous-waste contractor
Do Not: Dump in drains, surface water, or regular trash
Reuse/Recycling: Do not attempt unless specialized, properly equipped facility and technicians available
Laws: Follow local, regional, and country-specific disposal rules for selenium and its compounds
UN Number: UN 3283 (for selenious acid solution, regulated as toxic substance)
Hazard Class: 6.1 (Toxic substances)
Packaging Requirements: Use appropriate, sealed chemical-resistant drums or bottles; secondary containment strongly recommended
Labels: Display toxic and corrosive warnings clearly
Transport Precautions: Keep upright, avoid rough handling, comply with regulations for ground, sea, or air movement
Regulation: Listed under hazardous chemicals in most national inventories; workplace exposure limits enforceable in many countries
OSHA/NIOSH/EU: Worker protection rules for toxic and corrosive chemicals, environmental discharge strictly controlled
Reporting Thresholds: Significant quantities of selenious acid may need notification to health, safety, or environmental authorities
Community Right-to-Know: Expect strong labeling, training, and spill-reporting standards anywhere this acid enters daily work life
