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Substance Name: Selenium
Chemical Formula: Se
Appearance: It shows up as a gray, metallic-looking solid or as a red powder, depending on its form. Selenium gives off a metallic sheen when pure.
Odor: No significant smell under normal conditions.
CAS Number: 7782-49-2
Common Uses: You find selenium turning up in electronics, glassmaking, pigments, supplements, and sometimes agriculture.
Health Hazards: Breathing in dust or fumes can irritate the nose, throat, and lungs. Chronic exposure has been known to bring selenium poisoning. Selenium can cause garlic breath, irritated eyes, and, with high levels, symptoms like stomach upset, fatigue, and nerve issues.
Environmental Hazards: Dangerous to aquatic life at high concentrations. Persistent and can accumulate in some environments.
Risk Phrases: Harmful by inhalation and if swallowed. Prolonged contact can bring chronic health effects, including selenium toxicity.
Physical Hazards: Finely divided selenium powder may ignite easily. Bulk selenium resists burning.
Main Ingredient: Elemental selenium
Purity: Most commercial forms reach over 99% selenium content.
Impurities: Trace amounts of metals like tellurium or sulfur can sometimes be found, depending on the source.
Forms Available: Elemental (gray crystalline, amorphous), sometimes encountered as selenium compounds rather than pure.
Inhalation: If anyone inhales selenium dust, move them to fresh air. Medical attention can help for persistent symptoms like cough or trouble breathing.
Eye Contact: Rinse eyes with water for several minutes, keeping eyelids wide open. Seek medical help for lasting irritation.
Skin Contact: Wash the affected skin with soap and water. Remove any contaminated clothing. If rash or irritation follows, a doctor should check it out.
Ingestion: Rinse mouth. Seek immediate medical help. Do not try to induce vomiting without consulting a healthcare professional.
Suitable Extinguishing Media: Use dry powder, sand, or carbon dioxide for fires involving selenium, because water and foam may react with burning selenium.
Special Hazards: Burning selenium gives off toxic selenium dioxide gas and possibly hydrogen selenide. These fumes can be dangerous in enclosed spaces.
Protective Equipment: Firefighters need self-contained breathing apparatus and protective clothing, given the toxic fumes.
Precautions: Keep backs to the wind, work upwind, avoid breathing smoke.
Personal Precautions: Wear gloves, goggles, masks, and suitable protective clothing to avoid skin and respiratory exposure.
Spill Handling: Carefully scoop up solid selenium with non-sparking tools. For dust, dampen with water spray to prevent it going airborne.
Environmental Precautions: Prevent runoff into water bodies. Isolate the area to block unnecessary entry.
Waste Cleanup: Store in labeled, sealed containers. Dispose of with hazardous waste, never with general trash.
Handling: Use in well-ventilated places. Avoid actions that create dust. No eating, drinking, or smoking where selenium is handled. Clean hands and face after working.
Storage: Keep in closed, corrosion-resistant containers. Store away from strong acids, oxidizing agents, or food products. Keep far from moisture and ignition sources.
Special Notes: Treat as a hazardous chemical even when amounts seem small. A secure storage cabinet marked for toxic substances helps reduce accidental exposure.
Exposure Limits: Many countries limit selenium dust in occupational settings to 0.2 mg/m³ or less as an 8-hour time-weighted average.
Engineering Controls: Work under fume hoods or local exhaust fans. Routine air monitoring helps keep levels safe.
Personal Protection: Use NIOSH-approved respirators, splash goggles, gloves made of nitrile or neoprene, and lab coats or coveralls. Wash hands and face thoroughly before breaks and after shifts.
Industrial Hygiene: Regular workplace monitoring, health surveillance for those in contact with the material, and keeping eating areas separate.
Physical State: Solid
Melting Point: Close to 221°C
Boiling Point: Around 685°C
Density: About 4.8 g/cm³
Solubility: Insoluble in water, soluble in some concentrated acids
Vapor Pressure: Low at room temperature
Odor Threshold: High concentrations release a pungent, garlic-like odor
Other: Conducts electricity weakly, has several allotropes (forms).
Chemical Stability: Stable under normal conditions and away from incompatible chemicals.
Reactivity: Reacts with strong acids to form toxic hydrogen selenide gas. Reacts with oxidizers and halogens, sometimes with heat release.
Incompatible Materials: Strong oxidizers, strong acids, halogens, and certain metals.
Hazardous Decomposition Products: Selenium dioxide, hydrogen selenide, and other selenium compounds under fire or intense heat.
Acute Toxicity: Swallowing or breathing dust or fumes is harmful. Severe poisoning can bring nausea, vomiting, headaches, muscle soreness, and neurological symptoms. Children and pets have higher risk.
Chronic Toxicity: Ongoing exposure can result in hair loss, brittle nails, skin rashes, and neurological problems. Selenium can build up, leading to more significant long-term health effects.
Carcinogenicity: No strong evidence that selenium itself causes cancer. Some studies address the link between selenium compounds and health outcomes, but pure elemental selenium shows lower risk.
Other Effects: Large doses over time can bring a telltale garlic breath and a metallic taste, known signals of overexposure.
Ecotoxicity: Selenium at high concentrations builds up in plants, fish, and birds, causing reproductive and developmental problems. Some aquatic regions show dead wildlife from persistent contamination.
Persistence: Selenium binds to soils and sediments and resists breakdown in natural conditions.
Mobility: Elemental selenium is less mobile than many of its compounds, but selenium pollution from industry can travel through water systems.
Bioaccumulation: Moves up the food chain, showing up in fish, waterfowl, and other wildlife far from the original source. Chronic bioaccumulation disrupts whole ecosystems.
Waste Handling: Avoid tossing selenium waste in regular trash bins or pouring it down drains. Collect waste in labeled hazardous material containers.
Disposal Method: Send selenium and its compounds to authorized hazardous waste disposal facilities following local, state, or national laws. Do not incinerate or treat with acids due to risk of toxic gas.
Precautionary Step: Keep away from compost or municipal dumps. Encourage recycling and reclamation in industries that regularly use selenium.
UN Classification: Considered hazardous for transportation under many international guidelines.
Packing Group: Can fall under PG III depending on form and concentration.
Hazard Class: Generally classified as toxic solid or potentially dangerous substance.
Special Precautions: Secure containers against leakage, keep upright, handle packages to prevent dropping or breaking open.
Regulatory Codes: Shipment documents need proper names, hazard details, and emergency instructions, following protocols for toxic substances.
Workplace Safety: Occupational exposure limits are enforced by agencies such as OSHA, NIOSH, and their global counterparts. Inspectors look for proper labeling, training, and engineering controls.
Environmental Rules: National and local governments cap selenium discharges into water and soil, especially near agriculture and industrial sites.
Labeling Requirements: Containers and workplaces need clear hazard communication, including hazard symbols and handling directions.
Reporting Obligations: Many jurisdictions require reporting of significant spills or releases to environmental agencies.
Restriction on Use: Regulations sometimes restrict selenium in certain products like animal feed additives, limiting exposure for both humans and the larger ecosystem.
