Saturday, November 21, 2009

The Biochar PAH issue

The issue of PAH was the very first topic that arose during the inaugural meeting of the CBI in December 2008. We have talked a lot about PAH.

Of the resolutions of our meeting in December, we were to:

§ Facilitate links between industrial and research community.
"Research must be pushed towards demonstration with a focus on PAH’s, toxicity and decomposition by-products and any other unintended chemical or physical interactions."

§ Undertake technical specific work on developing biochar standards that address toxicity ie LDL 50 and PAH levels

A biomass stove expert from the National Renewable Energy Labs (NREL) in Colorado has undertaken quite an extensive review of the PAH issue and has spoken to several other NREL (and former NREL) personnel on this topic and has found “none with a major PAH concern related to biochar”, but he has suggested a need for more work.

He had indicated that he does not believe “this need be a very complicated study”. He added later that “it is important how the char and gases are separated” because it has been shown definitively that there is a hazard with the gasses (Diebold studies). He also said that many residual compounds are water soluble.

He did say that it might be a good idea to contact “experts studying char from the fire impact standpoint”. It has been suggested that “sediment researchers” be engaged to look at this.

Back in April this is what he had to say:
"I have looked at this issue every way I knew how and have found nothing definitive -- especially that char is definitively safe.”
“PAHs and dioxins certainly exist and are carcinogenic - but the only literature I have found says the PAH compounds are dangerous because they can be airborne (breathable - part of the gas output in the char production) and produced at much higher temperatures than the roughly 500C value (or less) that we hear proposed for biochar. I know of no literature showing a PAH hazard associated with char in the ground. In fact char seems more likely to be used to clean up PAH compounds from soil. We need someone to study this in more detail."

This is confirmed by the fact that Polycyclic Aromatic Hydrocarbons are US federally regulated “hazardous air pollutant” -- not a soil or water pollutant.

Marquita K. Hill, Second Edition, CambridgeU Press, 2004 stated:
i. “They bind to soils so tightly that even if ingested absorption is limited.”
ii. “Sunlight and warmth will degrade them.”
iii. “90% of human exposure is from food, especially leafy veggies and whole grains”
– most of this comes from airborne PAHs that have “settled onto food crops”
iv. “Even baked goods and toast typically contain them, created during the browning process.”
v. “Common in carpets, some babies have been found to be exposed to an equivalent of three cigarettes a day from their daily urban exposures.”

Here is one other study:

But I still think that Paul Stamets presentation on Bioremediation has incredible value:

If biochar stimulates AM Fungi, as has been indicated in many studies, then the “PAH issue” may not be as much of an issue as we believe it might be (even if the simple laboratory leachate tests indicate the PAHs are mobile and will leach out of the chars).

One likely cannot infer conclusions based on separating out a single test of a single parameter anymore. Hopefully science is evolving past this simplistic view and we are now capable of studying dynamic systems where a host of variables interact and create an outcome that cannot be predicted based on simplistic binary models.

Humans and all other organisms have evolved with PAHs in their environment, just like most other natural compounds that we might consider toxic.

I am FAR more worried about the “new” compounds that humans are formulating in laboratories and dumping into the natural environment in vast quantities. Compounds that nature has never been exposed to in its several billion years of evolution on this planet like organochlorine compounds, PFCs, PBDE (brominated) flame-retardants, chlorinated benzenes, chloroform, cyclohexane, octane, tetrachloroethylene, trichloroethylene, toluenes, phthalates, phenols, xylenes, surfactants and a vast array of unreported compounds of industrial origin -- and nuclear wastes, which can produce materials that have never before existed on earth and will likely never be assimilated into the tissues of living creatures.

Thousands of common synthetic (organic and inorganic) chemicals have been introduced into the environment over the past half-century that can mimic natural hormones, alter sexual and neurological development and impair reproduction. Dozens of studies have documented the impact of these endocrine-disrupting chemicals (EDCs) on animals, frogs, fish and birds with deformed genitals, brain damage, cancers and damaged reproductive systems.

Millions of tons of reproductive toxins are spewed out by facilities in the Sarnia area of Ontario year in, year out with barely a whisper. (In 2005, according to a study by the environmental NGO Ecojustice, factories in Sarnia released more than 131,000 tonnes of pollutants into the air.)

There are more than 80,000 chemicals in industrial production today with hundreds added each year. Few have been tested for their effect on human health or the environment. And, critically, there is almost no knowledge of how chemicals interact with each other to affect our health or the wider environment. When the Toxic Substances Control Act (TSCA) was passed in the US in 1976, more than 62,000 chemicals were ‘grandfathered’ into the market – i.e. no testing, no questions asked.

The Environmental Protection Agency (EPA) admits that 95 per cent of all chemicals in the US have not undergone even minimal testing for toxicity. In the European Union (EU) it’s estimated that two-thirds of the 30,000 most commonly used chemicals have not been vetted. The EPA has banned just five chemicals in the past quarter-century.

The air emissions from a properly designed Pyrolysis plant are far more likely to be clean.
Even a properly designed small stove that produces biochar (like the TLUD) is probably far, far cleaner than an open campfire. The air emissions from an industrial system were tested and it was found that “the total volatile emissions measured were only 8 ppm in their stack tests”. PAH levels were not measured, but were expected to be “non-existent”.

Fast pyrolysis char yields are rather small and the oxygen content is high, but the PAH and aromaticity was measured as being “low” (and it was shown to be “a good absorbent”).

Here is how summarized it:

"The formation of PAH during pyrolysis has been well documented (Painter, 2001; Ledesma et al, 2002) although the concentration and availability of PAH with respect to biochars is still uncertain. Garcia and Perez (2008) reported lower presence in bio-oils derived under fast pyrolysis conditions (<10>100 ppm). While PAH may be harmful to most plant and microbial communities, relatively rapid decomposition of these compounds by certain microbial populations has been observed (Ogawa, 1994; Zackrisson et al, 1996) and PAH compounds may be fully consumed within one to two growing seasons under many conditions (Thies and Rillig, 2009)."

I believe that many have come to these conclusions:

- There is no way you can expect simple answers about PAHs.
- Smoke contains PAHs. So all of the smoked Foods that you eat (from sausage to salmon) have PAHs in them. (Smoking food has been used for centuries to kill off the life forms that cause food spoilage.)
- People get routinely exposed to PAHs through regular daily exposure to things like BBQ dinners and coffee … and campfires, cigarettes, wood fireplaces, asphalt fumes, chocolate ( and fertilizers (

Consider this: What happens to the residual PAHs that are left on the floor of a forest after a forest fire?
Are these considered a health hazard?

Unpublished analyses of several biochar samples had found PAH content no greater than that of bulk soil (Manning, pers. comm.).
A single published study examined the full PAH profile (40 individual PAH compounds) in a number of synthetic char samples manufactured at relatively high heating rate concentrations (Brown, 2006). The total PAH concentration was 3–16 µg g-1, depending on peak temperature, compared to 28 µg g-1 in the char from a prescribed burn in pine forest.

It has been stated by Ahmed (1989) that "whilst biochar should contain systems of PAH, existing evidence indicates that no leachable PAH is present."
Source: Ahmed, A., Pakdel, H., Roy, C., Kaliaguine, S., 1989. Characterization of the solid residues of vacuum pyrolysis of Papulus Tremuloides. Journal of Analytical and Applied Pyrolysis 14, 281-294

One noted researcher has noted that “thermophilic bacteria” (such as in manure composts) "seems to be best at assimilating these compounds”.

Of course we would never advocate breathing the uncombusted fumes from pyrolysis – there are plenty of known carcinogens in the exhaust. We would never advocate dumping the pyrolysis oil into the environment either. There are dangers, yes, but I would be much more concerned about breathing in black carbon particulates from candles burned indoors -- or incense sticks lit deliberately to make the air smell of scented smoke. (I use them all the time!)

Yet candles are producing “Fine particulates" like PM 2.5's (being 2.5 microns across or smaller). Unlike PAH's, PM 2.5's are considered a "Criteria Pollutant".
"Fossil fuel combustion sources dominate PM2.5 emissions" (so) “controlling PM2.5 means reducing our dependence on fossil fuels”.

Someone recently noted that “the reality observed in the field is that microbes scour fresh biochar and eat up the tars & resins. They get energy from those polycyclic rings (of PAH and VOM); eat it like candy, I hear…”.

In another anecdotal story it was said that, “Recently a group in MA got permission to truck charcoal from an old CT industrial site to spread on farmland. The state agency required tests of this industrial brownfield residue, certain it would contain all sorts of toxic chemicals. The results came back unspectular and near-zero. Whatever residues of pyrolysis the charcoal once contained, after a couple of decades, the PAHs etc. were gone -- presumably from biologial breakdown, not weathering and leaching.”

In summary:

-Incomplete combustion produces the highest levels of the most dangerous PAH.
-Pyrolysis is not combustion.
-The amount of PAH depends both on pyrolysis conditions (e.g. Temp) and feedstock composition (e.g. presence of Chlorine can create dioxins)
-Dangerous Persistent Organic Pollutants (POPs) are listed in EU Regulation 850/2004
-There is No evidence of dioxins and furans in biochar
-There is Evidence of PAHs formed at temperatures between 350-600°C but it is certainly less than burning pine. [PAH] (3-16 vs 28 µg g-1)
-PAHs are very strongly adsorbed to biochar (due to planar C=C bonds)

M. Jones, E. Lopez Capel, D. A. C. Manning: Polycyclic aromatic hydrocarbons (PAH) in biochars and related materials.

Yes, we must use "the precautionary principle" when it comes to biochar in soils -- but we must also move quickly, for (according to many climate scientists) we may not have very much time to waste.

The conclusion:
"A careful, unbiased, and critical examination of the issue of PAHs is necessary."

This absolutely must be part and parcel of a comprehensive research project.

But, meanwhile, I'm going to consider stopping my use of candles and incense -- and go ahead and use biochar again in the soil of my balcony garden next spring.


  1. Hi Lloyd,

    This is such a helpful summary of information on this important concern. I am one of those people, who is out there introducing audiences to biochar's potential. And although I am careful to make it clear, that I am not a scientist, I have already had to field questions about this. Can I put this up on the SeaChar site?


  2. May I chime in .....BRAVO....Lloyd

    Your writing jives with all I've seen

    I think that a true point of traction for char will evolve from the Hormone induced tran-sexed fish. A Provocatively uncomfortable vision that begs for the char solution. (envisioning the corollary of the "Simson's" three eyed fish.)

  3. Great summary, would love to find out if PAH is the main issue or if there are other toxins to address in production of biochar.

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