When it’s time to dispose of chemicals in the laboratory, high school teachers have many sources for proper disposal guidelines… perhaps too many sources, if you ask me. While researching disposal issues for my own lab, I discovered that many colleges and universities have their own carefully designed protocols—and some even have people specifically tasked with overseeing the process and answering related questions.

Unfortunately, many high school teachers do not have such helpful guidance and resources. If your school’s or district’s Chemical Hygiene Plan (CHP) does not clearly outline disposal procedures (or if it doesn’t have a formal CHP to begin with), you may face a lengthy and frustrating process for finding the information you need to clean up your lab. This is especially true for teachers who don’t have a chemistry degree; vague recommendations to “weed out oxidizers” or “look up hazardous chemicals” don’t mean much if you can’t remember the necessary terminology or don’t have a strong chemistry background.

Some reasons to dispose of a chemical

  1. It is expired. Many companies now print expiration or purchase dates on their chemicals. Fisher Scientific recommends disposal after five years.
  2. Its condition has degraded. For example, if a hygroscopic chemical has taken on water, or a container was not sealed properly, disposal is recommended.
  3. You don’t use/need it. Keep track of the chemicals you use in demonstrations and labs, and dispose of those no longer required.
  4. It carries hazards to your laboratory instruction that outweigh the benefits.

Chemicals that should never be in a high school lab

Many schools and districts specify various reagents that are absolutely NOT allowed within schools. If your school or system does not provide such guidance, check out ACS’ Restricted-Use Chemicals, a set of general guidelines developed by the Committee on Chemical Safety. The ACS list, included in the broader publication “Reducing Risks to Students and Educators from Hazardous Chemicals in a Secondary School Chemical Inventory,” is extensive but not all-inclusive. Chemicals included are identified by whether or not they are explosives, toxic, irritants, carcinogens, corrosives, oxidizers, poisons, allergens, flammables, or capable of creating violent reactions. The intent of this list is not to prohibit the use of these chemicals, but to ensure that the classroom teacher is aware of their specific hazards. In my lab, I found a few “offenders,” including ammonium nitrate, lead (VI) chromate, sodium peroxide, and tin (IV) chloride, each are not recommended for use in the high school lab.

Chemicals that can go into the trash

Certain chemicals can be thrown away in the trash or dumpster at school. It is recommended that only small amounts be disposed of at any one time (no more than 5 or 10 lbs.), and only in tightly sealed containers. When I throw away chemicals in my lab trashcan, I always alert our maintenance staff, so that they can avoid any accidents in handling them. How do you know which chemicals are appropriate for trash disposal? Grab the Safety Data Sheet (SDS). If you don’t have these readily available, it is important to take the time to find them for each chemical in your laboratory. Chemical companies are excellent sources for these; I receive a disc containing SDS information with each chemical order I place, or you can search their websites.

To be safely disposed of in regular trash, an item must be:

  1. Nonradioactive
  2. Nonbiological hazard
  3. Neither flammable, reactive, corrosive, nor listed as hazardous waste per the Environmental Protection Agency (EPA)
  4. Not a substance that may negatively affect human or environmental health
  5. Not a carcinogen

SDSs have sections for each of these concerns, so the information is not difficult to find. However, this is a time-consuming process, and you will likely find some chemicals that cannot go into the trash. What do you do with these? I suggest setting them aside in boxes for hazmat pickup, but be careful: compatibility is an issue, even in disposal.

Incompatible chemicals

The following table is useful not only for storing chemicals safely, but also for placing chemicals in boxes or bins for disposal. As most high schools do not have frequent pickup of hazmat materials, old chemicals must sometimes be set aside for up to a year until pickup occurs. Consult this table to determine which chemicals may or may not be stored together. Download the full list of Incompatible Chemicals in PDF.

Chemicals that cannot go down the drain

There are several chemicals that absolutely SHOULD NOT go down the drain:

  • Halogenated hydrocarbons (chlorofluorocarbons, chlorocarbons, etc.)
  • Nitro compounds (nitroethane, nitrobenzene, etc.)
  • Mercaptans, also known as thiols (methyl mercaptan/methanethiol, etc.)
  • Flammables immiscible in water (hexane, toluene, etc.)
  • Explosives (azides, fulminates, etc.)
  • Water-soluble polymers (sodium polyacrylate, guar gum, casein, etc.)
  • Water-reactive materials (lithium, sodium, and other alkali metals)
  • Chemicals with a foul odor
  • Toxic chemicals (carcinogens, mutagens, teratogens; indicated on SDS)
  • Substances with a boiling point lower than 50 oC
  • Insoluble solids, including hair, ash, sand, metal, or glass
  • Oil or grease
  • Mixture that includes any of the above substances

    : Lab Waste Drain Disposal, Montana State University (accessed February 1, 2016).

Many of these substances will require hazmat pickup. However, for those that can go down the sink, remember to use the laboratory sinks ONLY, and never a storm drain that goes directly to a water source without treatment. When flushing chemicals, be sure ALL of one chemical is gone from the sink before a second chemical is flushed. Run an excess of water after disposing the chemical, even up to 100 times the original volume of which you disposed. On any given day, only dispose of a few hundred grams or milliliters, and check with your maintenance staff before disposing larger amounts.

Which chemicals are acceptable for drain disposal?

  • Those that meet criteria for trash disposal
  • Acids and bases with a pH between 5.5 and 10.5
  • Combinations of the cations and anions listed below (unless they are strong acids or bases). Please note, if you have a compound that is not a pairing of a cation and anion on this list, it is NOT safe for drain disposal and should be disposed with hazmat pickup.

What to do with hazardous materials

Hazardous materials provide a unique problem for high school chemistry teachers, because most of us do not have a quick and safe way to store or dispose of them. At my district, we have hazmat pickup once per year. Perhaps if my lab were completely cleaned out, this would not pose a problem, but as I continue to cull old chemicals, I continue to find dangerous ones. I recommend contacting your district officials to determine the date of the next scheduled hazmat pickup, or if they would prefer to have hazardous materials brought to a central location. If that is not an option, you should contact a nearby college or university. They tend to have more frequent pickup schedules and are typically happy to help local schools.

According to the Local Hazardous Waste Management Program (LHWMP) in King County, Washington, the three most common school lab hazardous wastes are heavy metal solutions (including chromium, copper, lead, etc.), organic solvents (hexane, benzene, toluene, etc.), and corrosive liquids (strong acids or bases). The LHWMP website includes these guidelines:

  1. Heavy metal solutions should be collected “in a single large wide-mouthed container lined with a sliding lock plastic bag. Leave the bag open so most of the water can be evaporated in a fume hood. When the bag is full of settled solids, zip it closed and place it in a five-gallon bucket labeled ‘Hazardous Waste – Heavy Metals’ and snap the lid closed. When this five-gallon bucket is full of bags of sludge, dispose of it as hazardous waste.”
  2. Organic solvents should be collected in a container with a tight-fitting lid and labeled as hazardous waste.
  3. Corrosive liquids, such as strong acids and bases, should be disposed of as hazardous waste. However, if appropriately diluted to a pH between 5.5 and 10.5, these can go down the drain.

You should keep a log of hazardous materials and waste to avoid extra costs associated with hazmat pickup. If technicians know exactly what is in your hazardous waste, they will not have to perform additional identification testing that will cost you money.

What to purchase to update storage

Be certain your lab has dedicated cabinets for flammables and corrosives. If not, this is an important purchase. Along with your chemicals, be sure to order new bottles for lab use. Keep or purchase extra glass bottles with tight-fitting lids for solvent disposal. Something that is often forgotten is labels; purchase new labels to keep careful record of your chemicals and their wastes.

Helpful tips

  • Contact a local college or university for assistance and possible hazmat pickup.
  • After the AP exam, your AP students could find and look over the SDS for pertinent information.
  • Do one shelf at a time.
  • Inform maintenance staff of your disposal activities.
  • Keep a list of incompatible chemicals in your storeroom and do a quick check each time you rearrange for disposal.

Planning ahead for next school year

  • Plan — Teachers must decide which chemicals are truly necessary in their laboratories, and safely dispose of the rest. This keeps dangerous materials and reactions out of the hands of students and avoids other problems.
  • Collect — When laboratory waste is not collected and handled correctly, it can threaten the health and safety of students and school staff alike. Keeping logs of hazardous waste and clearly labeling it as such are key parts of the solution.
  • Storage — A well-organized and maintained storage system for all chemicals, including wastes, is important for a safe laboratory. Be sure your waste storage space is secure and cannot be easily bumped or damaged.
  • Disposal — Remember, cleanup is not solely the teacher’s responsibility. Your local solid waste district can help you plan a hazardous waste pickup — ideally, at least once per year.

Credit: Ralph Stuart

Works Cited

  1. American Chemical Society. "Reducing Risks to Students and Educators from Hazardous Chemicals in a Secondary School Chemical Inventory," (accessed April 24, 2016).
  2. Lincoln University Police Department, Environmental Health and Safety. "What Material Can I Put in the Trash or Down the Drain?" 2013.
  3. Local Hazardous Waste Management Program in King County, Washington. "Proper Disposal of School Chemicals," (accessed February 3, 2016).
  4. Montana State University. Lab Waste Drain Disposal, (accessed February 1, 2016).
  5. U.S. Consumer Product Safety Commission. School Chemistry Laboratory Safety Guide, Oct 2006.


Special thanks to Ralph Stuart, CIH, CCHO, Chemical Hygiene Officer, Keene State College