Evaluating the Potential Risk of Dust Generated from Biochar-Amended Soils Using a Dust Generator.

While biochar is increasingly promoted as a beneficial soil amendment for some cropping systems, the potential hazards associated with biochar-containing agricultural dust, which can be exposed to farmers or nearby population, have not been adequately investigated. Through standard farming practices, such as tillage, biochar enriched dust can be inhaled into human’s respiratory system, be attached to human’s dermal tissues, or accidentally enter human’s digestive tracts. To develop best management practices for minimizing human health risks posed by biochar-containing dust, a series of dust generation experiments were conducted. Effect of soil texture (SiL, SL), biochar feedstock (ponderosa pine, walnut shell) and production temperature (500-900°C), biochar application rate (1, 2, 5% by mass), and soil water content (25, 50, 75% water holding capacity) was investigated. Results showed that coarse texture soils generated more dust than fine texture soils and that lower water content in soil resulted in more dust generation. In addition, soils amended by 5% biochar generated significantly larger amount of particulate matter than soils amended by 1% and 2% biochar. The black carbon content of the dust was determined using the benzene polycarboxylic acid (BPCA) molecular marker method. The BPCA results showed that, on a mass ratio bass, 1) increase in biochar application rate led to higher black carbon content of the dust; 2) coarse-textured soils have lower black carbon content in the dust fraction; and 3) increasing soil water content resulted in increased black carbon content, although overall dust generation was less. Bioassays to evaluate the toxicity of the bulk dusts, and relation to black carbon content, are ongoing and will provide important insight for developing management guidelines.