Safe Chemical Waste Disposal

By Dora Fatula

What’s the safest way to dispose of unused chemicals? It depends.

Your school or district should have a Chemical Hygiene Plan (CHP) that outlines disposal procedures. If no CHP exists, work with administration and local fire, safety, waste, and water authorities to create one.

Chemicals to Discard

Discard any chemicals that are:

• Expired – Expiration date has passed
• Old – No expiration date, but it has been on the shelf for more than five years
• Degraded – Was not properly closed, has absorbed water, or is otherwise compromised
• Superfluous – Not needed or being used
• Hazardous – Explosive, toxic, irritant, carcinogen, corrosive, oxidizer, poison, allergen, flammable, or violently reactive
• Prohibited – Refer to the ACS Restricted-Use Chemicals list*

*General guidelines developed by the Committee on Chemical Safety; includes an extensive but not all-inclusive list of chemicals that are inappropriate for high school labs.

Disposing of Chemicals in the Trash

Refer to a chemical’s Safety Data Sheet (SDS) to determine if it can be discarded in the trash or dumpster. If an SDS is not immediately available, contact the product or chemical manufacturer or search their websites. Also, check with local regulations before disposal.

Chemicals placed in the trash may not be:

• Radioactive
• Biologically hazardous or carcinogenic
• Flammable, reactive, or corrosive
• Hazardous (per the U.S. Environmental Protection Agency)

Alert your maintenance staff when placing chemicals in the trash to help avoid accidents.

Put the chemical in tightly sealed containers and discard only small amounts (no more than five to ten pounds) at a time.

Disposing of Chemicals in Water

Some chemicals may be diluted with water and flushed down the drain:

• Chemicals that meet the criteria for trash disposal
• Acids or bases with a pH between 5.5 and 10.5

Never flush halogenated hydrocarbons, nitro compounds, mercaptans, water-immiscible flammables, explosives, water-soluble polymers, water-reactive materials, foul-smelling chemicals, toxins or carcinogens, insoluble solids (hair, ash, sand, metal, or glass), oil, or grease.

Flush a single chemical at a time and follow each one with copious amounts of water. Dispose of only a few hundred grams or milliliters in a single day; check with maintenance staff before flushing larger amounts. Flush into the laboratory sink only and never into storm drains, which go directly to the water source without treatment.

Disposing of Hazardous Chemicals

Label, store, and dispose of hazardous chemicals carefully and maintain a log of what you are discarding. Hazardous materials may be collected only periodically, so proper storage until pick-up is critical. It may also be possible to drop off hazardous chemicals at remote collection locations, another school, or other facilities that have regular pick-ups.

Sequester chemicals that cannot be safely stored together, and make sure to place them in dedicated cabinets for flammables and corrosives. Some common school lab hazardous wastes include:

• Heavy metal solutions (including chromium, copper, and lead)
• Organic solvents (like hexane, benzene, and toluene)
• Corrosive liquids (strong acids or bases)