Environmental implications of residual pyrogenic carbonaceous materials from incomplete biomass combustion: a review

Incomplete biomass burning produces considerable amounts of pyrogenic carbonaceous materials (PCMs), which are widely distributed in environmental matrices. Those PCMs undergo different environmental processes and consequently have non-negligible impacts on the global carbon cycle, ecological functions and environmental security. This review provided a comprehensive review of qualitative and quantitative methods, carbon sequestration capabilities and other ecosystem functions of PCMs. In addition, the generation mechanism and environmental health risks of emerging contaminants, especially persistent free radicals (EPFRs) and polycyclic aromatic hydrocarbons (PAHs) associated with PCMs were discussed. The results showed that the coexisting kerogen and coal may interfere with PCMs quantification, and that estimates of PCMs pools vary significantly due to methodological differences, natural variability and limited spatial coverage. The input of PCMs into soils increased soil carbon sequestration through direct carbon contribution and indirect negative priming effect on native SOC. In addition, PCMs can improve soil structure and properties and immobilize/degrade pollutants, which is conducive to the restoration of soil ecology. However, various contaminants associated with PCMs may threaten ecological safety, and thus their formation mechanisms and toxicological pathway to living organisms need to be further investigated. The development of standards for PCMs identification and quantification, application protocols of PCMs in pilot scale, and assessing the effects of PCMs on soil health deserve extended studies.