During the biochar production process, steps can be taken to create a safer, more effective soil amendment. As heavy metals and metalloids are concentrated in biochar through thermal conversion 
, the use of treated feedstocks such as chromated copper arsenate (CCA)-pressure treated wood should be avoided, along with materials from construction and demolition, and feedstocks of unknown origin. Research suggests that slow pyrolysis may minimize biochar PAH content compared to gasification, and that increased residence time 
and rate of carrier gas flow 
can offset PAH formation under high temperatures. There may also exist simple pre- and post- production modifications that reduce levels of contaminants. Studies indicate that drying feedstock biomass prior to pyrolysis may reduce production-related PM10
emissions, as well as PM-bound PAHs, as the presence of moisture encourages the incomplete combustion of volatile compounds formed during pyrolysis 
. Research has also demonstrated that biochars can be dried at temperatures between 100 and 300 °C, effectively removing PAHs through thermal desorption within 24 h 
. Efforts have also been made to improve the physical properties of biochar during its production. An increasingly popular technique is to pelletize biochars to increase resistance to abrasion 
. Addition of binders during pelletization, such as lignin and Ca(OH)2
, can further enhance the mechanical strength of biochars 
. With increased mechanical strength and abrasion resistance, biochar may emit less dust compared to those that have not been compressed.
Major (2010) summarizes various biochar application methods and recommends combining biochar amendment with other on-farm processes to reduce costs and to minimize the potential for dust emissions 
. Suggestions include adding biochar to compost or liquid fertilizer. To reduce dust emissions, recommendations for applying biochar with high moisture content or in liquid slurries are common, as are warnings to avoid application on windy days 
. While most biochar field trials utilize a broadcasting application technique (Figure 3
d), Major (2010) suggests that subsurface banding (Figure 3
a–c) may have the greatest potential to reduce wind and rain-driven biochar losses. Regardless of application method, the use of appropriate respirators, eye protection, gloves, long sleeves, and pants is recommended for farm operators and workers while handling biochar 
Governments can play a key role in developing and enforcing policies that ensure the safe production and handling of biochar. The United States has not yet adopted required regulatory standards for biochar contaminant levels (e.g., PAHs, heavy metals), though maximum threshold values for a limited number of toxicants have been established in frameworks proposed by the European Biochar Certificate (EBC) 
and the International Biochar Initiative (IBI) 
. As of June 2021, IBI lists four biochars certified to meet their safety and quality standards, all of which are in the United States 
. EBC lists 27 certified biochars from Austria (3), Finland (1), France (1), Germany (11), Romania (1), Serbia (1), Sweden (4), and Switzerland (5) 
. Differences in these standards have led to inconsistencies in both scientific and legislative literature. There is a pressing need for a unified regulatory framework, which would facilitate communication in academic fields and in the emerging biochar market. Furthermore, outreach and education efforts could assist in ensuring the safe application of biochar to working lands. This may be particularly relevant when biochar is paid for by government cost-share or incentive programs as part of climate change mitigation strategies. In these cases, agencies could require producers and land managers to review simple best management practices for the safe and effective use of biochar.
3. How Can We Best Move Forward?
Scientists have a critical role in ensuring that the current boom in biochar research produces information for its safe and effective use, which optimizes benefits for humans and the environment. We propose that by working together as a scientific community, the following strategies can assist in this goal, and in doing so, increase the rate of knowledge accrual to match the rate of investigation.
1. Results and conclusions from biochar studies should be limited to the specific conditions in which results were observed. Biochar has great potential to deliver numerous agricultural and environmental benefits. However, it has many variables and will perform differently in different conditions. While the enthusiasm of the day is useful for driving research, generating awareness, and leveraging funding, scientists should be careful to manage expectations and avoid generalizing their data to indicate that results extrapolate to other biochars or conditions.
2. Researchers should strive towards standardized biochar characterization methods and increased reporting of biochar production parameters and physical and chemical properties. In order to increase the efficacy of biochar for specific applications, it is necessary that researchers and biochar producers have access to comprehensive biochar production and characterization data. This is necessary for replicability of research, to guide decisions for biochar selection based on intended use, and to assist in tailoring biochars for specific purposes.
3. Biochar must be studied in real-world conditions to evaluate its long-term effects on soil productivity and health. There is a pressing need for long-term field-scale research utilizing commercially available biochars with high consistency in composition. As in all scientific fields, the pressure to produce results within a single grant cycle or graduate student tenure is an obvious challenge. However, our current reduced rate of knowledge gain will persist if we do not push experimental designs towards real world conditions. Only then can we better understand the benefits, drawbacks, tradeoffs, and costs associated with the production and use of biochar.
4. Results from biochar studies should always be explained on a physical, chemical, or biological basis. While field-scale research is critical, it is not sufficient for scientists to present results without further investigation into their mechanistic underpinnings. In order to advance the state of knowledge about biochar, results must be supported by mechanistic experimentation or explanations supported by other evidence.
5. Soil scientists cannot ensure the sustainable and effective production and use of biochar alone. In the research arena, there should be increased collaboration with industrial and material scientists in order to link biochar production parameters with specific characteristics. Groups of collaborators could work with large-scale biochar companies to produce biochars that are tailored for specific outcomes within certain soil and climate parameters. In the policy arena, scientists can guide the safe and effective use of biochar by working with governments to develop policies that require a specific O/C ratio for maximum C sequestration benefits. Policies should also be developed which require biochars to conform to safety standards. Finally, policy could assist in outreach and education efforts, so that biochars amended to working lands are applied in ways which safeguard human and environmental health.
6. Scientists, entrepreneurs, and other stakeholders should use creativity in discovering novel and beneficial uses for biochar. While research has demonstrated that biochar can improve soil health and agricultural production under specific conditions, its use in climate change mitigation, remediation, and product substitution may provide greater environmental benefits, with fewer potential unintended consequences. We must “think outside the soil” to advance biochar research towards new frontiers.
7. Biochar investigation should prioritize maximizing its numerous potential benefits. The technologies which convert waste biomass to biochar, bioenergy, and pyroligneous acid, have great potential to operate within “closed loop” systems if optimized properly. Locally sourced feedstocks can be converted to a range of coproducts, which can then be used locally for ecological, environmental, or agricultural outcomes. In temperate climates with fertile soils, biochar may be less useful as an agricultural soil amendment, and more beneficial in the remediation of contaminated sites, in storm or wastewater management, as a substitution for mining GHG-intensive materials, or modified to retain nutrients in compost production. If produced and employed thoughtfully, biochar has a high probability of serving as a climate mitigation tool. The key is to extract as many possible benefits from biochar production systems for multiple and variable uses.
While current efforts have largely focused on the potential of biochar to increase agricultural production and soil health, biochar research need not focus on soil alone. Biochars are a category of materials that can provide numerous benefits, and should be employed in a manner where they best address global sustainability constraints including, but not limited to, climate change, soil and water contamination, and productivity in marginal lands. In order to increase the current rate of knowledge accrual, scientists, policymakers, and entrepreneurs must work together to develop new and innovative approaches to biochar research, which address both safety and sustainability.