Biochar Risks, Health and Safety

Can biochar be contaminated?

All biomass feedstocks contain chemical compounds (sometimes contaminants) that may pose environmental or health risks when converted to biochar, but they only pose these risks if they are at a high enough concentrations.

Always know where your biochar is from and if being used to produce food, always make sure it is tested and fit for purpose.

Waste in general tends to contain contaminants. Biodegradable wastes are the most common examples of biomass feedstocks that may contain high levels of contaminants. However, higher levels can also occur in virgin or unprocessed feedstocks under certain environmental conditions or because of the process by which biochar is produced. Feedstocks that could be contaminated by their environmental conditions are those grown in contaminated land or railway embankments.

Contaminants which have a higher boiling point (higher than the temperature at which biochar is produced) will remain in the biochar and will become concentrated. This happens because 3 tonnes of biomass are needed to produce 1 tonne of biochar. Therefore if your biomass feedstock has a certain level of contamination, it might end up concentrated to higher levels in the biochar produced than in the feedstock.

What are the most common contaminants that are present in biomass feedstocks and that could potentially be transferred to the biochar produced?

The two most common contaminants are heavy metals (such as cadmium, copper, chromium, lead, zinc, mercury, nickel, arsenic) and Polycyclic Aromatic Hydrocarbons (PAHs). Heavy metals poison the body and damage organs. PAHs are also poisonous and some are associated with cancer.  Heavy metals and PAHs are naturally occurring substances and we are all exposed to PAHs every day at very low levels in the air we breathe and the foods we eat. As with all contaminants, what matters is the dose – everything is a poison if you are exposed to too much of it.

Always know where your biochar is from and if being used to produce food, always make sure it is tested and fit for purpose.

Our bodies require small amounts of some heavy metals, such as copper or zinc.  Others, such as mercury, lead, arsenic, and cadmium have no known benefits to our health. The excessive build-up of these heavy metals results in a toxic overload because our bodies are unable to metabolize them and thus, they accumulate in the soft tissues. Over time, this accumulation can cause serious illnesses.

Metals are found in all organic feedstocks but, provided that the biomass is clean and grown in non-contaminated soils, the concentration of these metals will usually be so low that there is no risk to humans or the environment, not even when the biomass converted to biochar.

However, organic wastes such as industrial and wastewater sludges (sewage sludge), construction and demolition wood (treated wood), ‘biosolids’ produced through a process called ‘anaerobic digestion’ of, e.g., sewage sludge or even food waste, all commonly contain heavy metals such as cadmium, copper, chromium, lead, zinc, mercury, nickel, arsenic at relatively high levels, even before their conversion to biochar.

Another type of contaminants are the so-called ‘organic’ chemicals. These are molecules that are – in some ways – similar to those which make-up living tissues of plants and animals.  Some of these molecules, which scientists know as ‘PAHs’, can be carcinogenic and only minute amounts are permitted in foods. This is why it is important to understand if the biomass feedstocks that you are going to use to produce biochar could potentially contain these contaminants.

Moreover, if biochar is made from feedstocks contaminated with plastics, it is possible that ‘dioxins’ could be produced. Dioxins are toxic and can cause cancer as well.  It is essential then to separate plastic contaminants from the biomass feedstock so that these dangerous chemicals do not find their way into the food chain by adding them via biochar to soil.

If you are not sure of the type of contaminants your feedstock could have, please contact us and we can help you in sorting out this matter.

Are there any Maximum Permissible Limits (MPLs) for potential contaminants in biochar for the UK?

No, at present there is no guidance or set  MPLs for biochar in the UK. The BQM will be finalised this year(2014) which will not only give guidance on MPLs but also sustainable and clean production in the UK. 

Limits on the maximum level of each potentially harmful chemical in a material to be added to the soil are set by government regulators and these are known as ‘maximum permissible limits’ (MPLs). If the level of a contaminant in biochar were to fall below the MPL for that contaminant, it would be considered safe for use in soil.

At present Scotland is the only country within the UK where the regulator allows use of  certain types of organic waste to produce biochar and then for this biochar to be used for agricultural and ecological benefit under exemption. Although there are no set levels of MPLs at present within the recent regulatory position statement issued by the Scottish Environment Protection Agency (SEPA), there is consideration for contamination as it only allows for the usage of biomass that is unlikely to have high levels of contaminants, such as untreated wood waste from agriculture, horticulture and forestry activities.

Click here to view the regulatory position statement.

The European Biochar Certificate provides guidance on MPLs in biochar for use in soil in their accreditation system, which can be found at the following link:

The International Biochar Initiative (IBI) have also produced voluntary guidelines for biochar that is used in soils, which include MPLs for heavy metals and organic pollutants. The guidelines can be found at the following link:

The Biochar Risk Assessment Framework (BRAF) is developing the BQM(Biochar Quality Mandate) that is geared to the UK context.  This is being developed with the regulators and technical experts.

More information about BRAF can be found at  the following link:

What are the risks identified so far by BRAF for biochar usage in soils?

The preliminary results of BRAF suggest that biochar produced from unprocessed feedstocks should normally pose no risks to human/animal health, even if added to grasslands and fields where crops are grown in large quantities and over a large area.

When processed (non-virgin) feedstocks are used for making biochar, it is recommended to use low application rates. The contaminant concentrations need to be below the MPL identified by the IBI and EBC in order to avoid any potential risks.

A risk traffic light detailing what could be adequate application rates for biochar produced from processed feedstocks will be added shortly in this website.

Are there any occupational health and safety risks with producing or applying biochar to soils?

When using or applying pure biochar caution needs to be taken as a fine dust can arise from the biochar. Breathing in very small particles is known to pose various health risks including respiratory diseases and even cancer. Such risks are usually associated with prolonged exposure to small particles through employment, e.g. in coal mining, quarrying or old style charcoal making. However, for the vast majority of biochar applications, a simple face mask would eliminate any risk and constitutes best practice.

Are there any potential risks to the environment from biochar? 

As long as biomass feedstocks come from recognised sustainable sources and best practice is used in biochar production and application, there are no environmental risks known to date.

The production of biochar at a medium or large scale could introduce additional risks to the environment such as deforestation or the use of land for biomass production that could and should be used to produce food.  There is a limited area of land available for food production and diverting land to produce biomass for fuels or biochar can push up food prices, as well as encouraging the conversion of agricultural land for use as additional non-agricultural land.  This can have a knock-on effect in encouraging conversion of forests and undisturbed areas for food production, with detrimental impacts on biodiversity (plants and animals), local food security as well as releasing carbon stored in soils to the atmosphere.

These risks are generally only associated with those biochars that are produced from unprocessed feedstocks, like virgin timber and energy crops.  It would be more sustainable to use processed feedstocks, such as organic wastes, cuttings from park and public spaces, household and urban green waste or the timber industries waste.

BRAF is developing a “sustainable biomass provision” scheme for biochar production. This scheme is based on the requirements of the EU Renewable Energy Directive (RED) that apply to solid biomass treatment (currently voluntary in each of the EU Member States), and will be updated to comply with the sustainability requirements proposed by the UK Department of Energy and Climate Change (DECC) that are currently under consultation. Since April 2011, DECC has required sustainabilty assessment for soild biomass and biogas that receives funding support under the  Renewables Obligation (RO).

RED recommends that sustainability schemes should be designed and implemented by biomass-based operations that generate above a certain level (1 Mega Watt thermal or 1 Mega Watt electrical capacity or above). A summary of BRAF’s proposal on this topic can be found at this link:

Can biochar be certified as safe to use in soils?

Yes. but present there is no biochar accreditation service In the UK.  The British Biochar Foundation is working towards offering accreditation of biochar as demand increases.This is something companies can approach the European Biochar Certificate for which does offer a voluntary system today. 

The European Biochar Foundation has developed a European Biochar Certificate (EBC) which is already being used by several biochar producers in Europe. In the UK, we are moving towards a biochar certificate and see this as one of the functions of the British Biochar Foundation (BBF). Other professional accreditation agencies operating in the UK may also be in a position to provide appropriate accreditation for biochar and biochar blend applications to soil. However, at the moment, these does not take into consideration sustainable feedstock provision and clean production methods.

In order to be accredited, biochar needs to have been tested for its contamination levels and should be fit for purpose under UK environmental law and accreditation standards.  But as long as you know your biochar is tested and is clean and free of heavy metals and organic contaminants, then it will be safe enough for you to grow and eat food from soil containing that biochar. If you don’t, we suggest that you only use this type of biochar for non-food crops or innovative carbon storage ideas.