Most solvent waste from US academic labs ends up in the air

Daily solvent use is pretty much a given in a synthetic chemistry lab.

In academic laboratories, it’s such an ingrained part of research that chemists might forget that solvents can be serious safety and health hazards. Commonly used solvents tend to be flammable and carcinogenic, and many can cause organ damage and even death from overexposure. The US Environmental Protection Agency recently added new restrictions and safety measures to the lab favorite dichloromethane because of its adverse health effects.

Solvents aren’t so great for the environment either. Most are classified as hazardous waste and are known to kill fish, pollute the air, and make water undrinkable. But what many chemists either forget or don’t realize is that using solvents in research contributes to climate change.

That’s because a lot of the solvent waste that comes from academic labs is burned, sending carbon dioxide into the air. Between 2011 and 2021, academic labs in the US generated an average of 4,300 metric tons (t) of hazardous waste a year. Almost half this waste is solvents, and more than half the hazardous waste is burned.

Although the ideas and practices of green chemistry are spreading, the amount of waste US academic labs produce annually has stayed roughly the same. C&EN analyzed 10 years of Resource Conservation and Recovery Act (RCRA) biennial hazardous waste reports from US colleges and universities and uncovered the amount of waste that academic labs produced, what kind of waste it was, and what happened to it.

The RCRA’s manifest system was designed to allow the EPA to track hazardous waste “from cradle to grave,” the agency says on its website—who generates it, who ships it, and where it ultimately ends up. But C&EN’s analysis found that with the information publicly available, it’s nearly impossible to follow the trail to the end. As a result, the amount of waste that is burned is greater than what the data show.

Where the waste goes

Most US colleges and universities have a waste day. Lab workers corral their bottles of waste, which they’ve labeled with full chemical names, the date they started collecting the waste, and the hazards of the contents.

They wheel these to the school’s collection site, where environmental health and safety (EH&S) workers check the tags, take the bottles, and typically dump the contents of bright-red reusable solvent cans into blue, metal 55 gal (208 L) drums. The EH&S staffers then organize and catalog the waste and put it into a storage area until a hazardous waste shipper comes to pick it up.

The first stop after pickup is usually a hazardous waste treatment, storage, and disposal facility. These are EPA-approved sites that have permits to deal with lab waste, says Becky Neal, a compliance manager at Envita Solutions, a waste management company.

The RCRA hazardous waste forms list over 20 methods for waste management, but according to C&EN’s analysis, most academic waste generated in the US is dealt with in one of three ways: from 2011 to 2021, about 19% was used for fuel blending, about 28% was incinerated, and about 46% was bulked, or combined with other waste.

Lab waste that is a mixture of nonhalogenated organic solvents typically gets the fuel-blending treatment, Neal says. This essentially means that the solvent is burned to power a kiln used to make portland and other types of hydraulic cement.

Cement production is notoriously energy hungry. On average, it takes about 3.4 billion J of thermal energy—a little more power than a typical single-family home in the US uses in a month—to make 1 t of cement. The solvents are an alternative to coal, the more common power source for cement kilns.

But because the kilns are heated to between 980 and 2,200 ˚C, operators have to be picky. They can use only materials with more than 5,000 Btu per pound (11,630 J/g), and the fuel mixtures generally need to be free of halogens.

The second major way to deal with hazardous waste from labs, incineration, is pretty much what it sounds like. “It’s combustion without energy recovery attached to it,” Neal says.

Incineration is the disposal method of choice for high-Btu solvent waste that can’t be used for fuel. “Usually, it’s because there’s something particularly nasty mixed in with it, such as some pesticides and other compounds with acute toxicity,” Neal says. The EPA requires that acutely toxic compounds be heated to temperatures higher than those generated by cement kilns to ensure that the compounds are sufficiently destroyed.

Incineration is also the fate of most halogenated solvent waste, which usually can’t serve as fuel for cement kilns because it doesn’t meet an EPA requirement to be broken down into carbon dioxide, water, and hydrohalic acids in under 2 s at 1,200 ˚C. Regulators also require incinerators that burn chlorinated solvents to scrub the gaseous waste stream for hydrogen chloride before it hits the atmosphere.

Some incineration or fuel blending happens at the initial hazardous waste treatment, storage, and disposal facility, Neal says. But in many cases, the waste moves on. Often, waste-handling companies bulk materials in the same waste class. “So they may have several drums of solvent mixtures from various industrial facilities or universities,” Neal says. Workers combine the drums’ contents into a tanker car or railcar and send them to another facility, usually one with an incinerator or a cement kiln.

According to C&EN’s analysis, 48% of hazardous waste generated from 2011 to 2021 in US academic labs was bulked. But what then happens to that waste is not clear. Under RCRA rules, the facility bulking the material fills out a new manifest with a new tracking number and lists itself as the generator. This process means that the hazardous waste’s initial tracking number can’t be used to continue following the waste.

The upshot is that the amount of waste that’s burned, either for fuel or destruction, is significantly greater than what the EPA’s data suggest.

What’s in the bottle?

The waste generated by academic labs in the US is mostly spent solvent. But just as we don’t know how much waste is burned, so we don’t know the details on exactly what the solvents are.

According to C&EN’s analysis, 29% of hazardous waste generated in US academic labs from 2011 to 2021 was a mixture of halogenated and nonhalogenated solvents, about 20% was nonhalogenated solvents, and close to 16% was made up of what are known as lab packs. The remaining 37% is a hodgepodge of aqueous waste, other organic liquids, other halogenated solvents, acids, acutely toxic waste, and more.

The labels “a mix of halogenated and non-halogenated solvent” and “non- halogenated solvent” are about as specific as the RCRA biennial reports get. And “lab packs” is even more ambiguous. These packs are smaller amounts of waste in individual containers, packed together in barrels with vermiculite to soak up any spills that might occur in transit. But after the lid goes on the barrel, what exactly is in them is hard to pin down.

“The lab pack is allowed by both EPA and US Department of Transportation, as long as the materials are part of the same hazard class and are compatible,” says Rex Howard, the lead hazardous materials specialist at Indiana University Bloomington (IU). The lab pack rule allows EH&S workers to ship out smaller amounts of materials and helps shield them from chemical exposure.

“So let’s say I get a 3 L bottle of hydrochloric acid from [a] lab. I never take that material out of its packaging. I leave it in that bottle,” Howard says. When the hazardous waste transporter comes to pick up the waste, they pack it into a 55 gal (208 L) fiber drum, along with a list of everything in the drum. This is a more streamlined list than what is on the individual waste tags filled out for waste day. “And in many cases, those lab pack drums just end up going directly to an incinerator,” Howard says.

Lab pack waste does have individual waste tags saying what’s in the packs and any appropriate hazards. “The little tag is part of our cradle-to-grave hazardous waste tracking,” Howard says. Schools’ EH&S departments have to keep the tags for at least 3 years after the waste is shipped off-site. Some universities have online systems to track their waste, but the details don’t make it onto the RCRA biennial reports and aren’t available to the public.

The tagging system also doesn’t require more details on containers of mixed halogenated solvents or nonhalogenated solvents. Hazardous waste transporters weigh the solvents, containers and all, and then cart them away.

The big picture: It’s small

How much does academic waste matter, in the grand scheme of things? Waste from academic research is a tiny portion of the hazardous waste generated in the US—0.005% in 2021.

The amount of waste coming from academia isn’t necessarily the issue, says Adelina Voutchkova, director of the American Chemical Society Green Chemistry Institute (GCI). C&EN is published by ACS but is editorially independent. The important part is building greener habits.

“It’s not a number that we’re trying to reduce for its own sake,” Voutchkova says. Rather, reducing solvent use in academic labs translates to reductions on a much larger scale when researchers transfer these processes to industry, she says. “Hopefully, some of the processes being developed will lead to patents, lead to commercialization, and lead to process development that’s relevant for making chemicals that aren’t part of the research in academia.”

There are few, if any, solvent-reducing programs that directly target professors or research leaders in charge of academic labs. “We teach workshops primarily focused to graduate students to help them see where they might be able to change the practices in their labs,” the GCI’s Voutchkova says. “They’re making some of the microdecisions that lead to those changes.”

In addition, knowing green chemistry practices such as reducing solvent waste or switching to greener solvents will help students get jobs in industry. “These are practices industry wants them to be able to adopt and skill sets they want them to have,” Voutchkova says. Companies are pushing academic labs to improve their research practices so they line up better with the way people increasingly do commercial research.

Ultimately, how much and what kinds of solvents academic labs use are up to the professors and principal investigators that run them. The professors in charge of research groups generally have a certain way they want lab work done, IU’s Howard says.

The amount of waste a school generates also depends on the nature of the research groups and the size of the department. And these factors can change with each academic year. The number of students starting and departing fluctuates continually, and sometimes whole labs leave.

At IU, an organic chemistry professor just moved to another school, taking his research group with him, Howard says. Since the organic groups tend to produce the most solvent waste, Howard predicts that IU’s output will measurably decline “until he’s replaced with another organic chemist.”

But some academic leaders are actively trying to reduce their labs’ waste. For many years, organic chemist Bruce Lipshutz has been working to switch from organic solvents to water in his lab at the University of California, Santa Barbara. As a result, the amount of hazardous waste his lab produces has dropped. Organic chemist and Nobel laureate Ben L. Feringa and colleagues at the University of Groningen recently published a paper on calculating their research’s carbon footprints and their efforts to make their labs more sustainable.

If researchers want to switch out hazardous solvents for greener ones, the GCI’s Voutchkova points to the institute’s solvent selection tool. Developed by industry, the tool provides guidance on what greener solvents might work for researchers’ systems. The choices that researchers make in the solvents they use can ultimately have a big effect, she says, for both their health and the health of the planet.