Toxicity of chimney creosote to environment?

August 26, 2019 8:49 AM

Every year I clean out the soot/creosote that's fallen to the bottom of my wood stove chimney and toss the maybe 4 gallons of it "over the bank" onto an old brush pile. I've begun to wonder if this is a bad practice. I could as easily landfill it or take it to a hazardous waste collection. As always, fact-based answers please
posted by Hobgoblin to Home & Garden (10 answers total)

Best answer: It's actually very good to add to garden soil! I also have a wood stove and it's good way to add nutrients. Veggies love it. You use it in different ways depending on what you'll be planting. Here's an article explaining it in detail.
posted by ananci at 9:14 AM on August 26, 2019 [2 favorites]

Best answer: I work in the environmental field, though IANY environmental consultant. I'm not that familiar with the materials used in wood-burning stoves, though we do look for various types of ash (typically coal ash) in historic fill, as it can leach metals and PAHs to the environment.

In terms of toxicity, here's the info for croeosote (PDF) from ATSDR (link 2 - web page for creosote) - which is where we go as a primary source. It looks like creosote, like ash, will leach PAHs, which is not great.

In terms of disposal, it looks like you'd be fine landfilling it. Also from NYS Dept of Env. Conservation - while you may not live in NYS, your state may not have anything specific listed based on the first link.
posted by DoubleLune at 9:17 AM on August 26, 2019 [1 favorite]

Best answer: It’s important to note that most safety data on creosote, and eg this CDC data sheet also linked above is for pure creosote, and applies to the purified liquid substance extracted by industrial processes and used to do stuff like treat railroad ties.

There is creosote in your chimney soot, but there’s a also huge amount of inert carbon and other completely harmless stuff.

I cannot easily find a source for how much creosote is in chimney soot, but keep in mind creosote is only a portion of what you’re dealing with, technically speaking, even though many/most people call the whole mix creosote too.
posted by SaltySalticid at 10:31 AM on August 26, 2019 [1 favorite]

Best answer: When I have the chimney swept, the sweep says to burn it. It is a product of incomplete combustion, burns well. I try to have at least 1 hot fire a week during heating season, chimney stays pretty clean, so I don't get much crud. I would not burn it all at once, would add a scoop at a time to a hot fire. I think it burns hot and fast; too much heat, too fast, in a cold stove, is not a good idea.

Unseasoned wood creates way more creosote.
posted by theora55 at 12:16 PM on August 26, 2019 [1 favorite]

Best answer: Like any soot, as other have said, it contains low levels of biologically active compounds including PAHs, dioxins, furans and other products of incomplete combustion. The links to summaries provided by DoubleLune and SaltySaltcid are excellent and the ones I have used to advise responders during fires. It is somewhat carcinogenic, but there are also many natural degraders in the environment. Soot and wood burn residues are natural and a normal part of the ecosystem. The major health risk however, is physical, from fine airborne particles.

To you personally, soot is a significant respiration and ingestion hazard. You should always wear a fine particle filter mask and avoid skin contact when handling it. A good cartridge filter/APR PM2.5 filter that covers your mouth and nose (and not just a paper n95 filter) is what I would recommend, as well as an impermeable/"rubber" glove.

Generally, burn residue is fine in normal landfill. Again, only for woods. If you've been burning a lot of other things, in particular plastics or other chemicals, the advice is very different.

I'm in a relevant environmental field, and have a number of publications on the fate and toxicology of fire residues.
posted by bonehead at 12:58 PM on August 26, 2019 [2 favorites]

Best answer: a <<secondary>> ingestion hazard. Sorry for any confusion.
posted by bonehead at 1:04 PM on August 26, 2019

Best answer: @bonehead, you seem to have more facts at your fingertips than me, but I would just comment that I would not expect soot from firewood to contain dioxin or furans because I do not think firewood contains much in the way of halogens like chlorine or fluorine. I think that those things come from house fires, when all sorts of synthetic chemicals are burnt. Would you agree?

Personally, I would not have any problem burying small amounts of soot and even creosote in my yard. I expect the amounts of hazardous chemicals would be de minimis. Sort of the same way that our health department advises homeowners with leftover paint to allow the solvents to evaporate so the paint solidifies and can be put into the landfill. Sure, that is some toluene in the air, but not much.
posted by hypnogogue at 5:02 PM on August 26, 2019

Best answer: Dioxin and furan are partially oxygenated hydrocarbons, and do occur naturally by wood combustion, particularly for fires that are low in oxygen. The ones that are of great toxic concern are, as you note, the halo-derivatives, particularly the chlorinated ones. This is a common issue with the old nomenclatures, they confused the parent base structures with the much more dangerous chloro derivatives. As a result, those more dangerous compounds are often called now polychloro dibenzodioxins (PCDDs) and polychloro dibenzofurans (PCDFs).

The great majority of aromatic compounds, including partial oxygenates like dioxin and furan, and their relatives, are cancer concerns. But it is true, the halo-derivatives are much more dangerous. In cases where the fire includes plastics or other potential sources of halogens, the level of protective equipment needed is much higher.
posted by bonehead at 7:39 PM on August 26, 2019 [1 favorite]

Best answer: Thanks, bone, that makes sense.

Back to the OP, I agree with ananci, by analogy with slash-and-burn agricultural practices.
posted by hypnogogue at 11:55 PM on August 26, 2019

Response by poster: Thanks everyone. You answered my question!
posted by Hobgoblin at 6:20 PM on August 27, 2019