Biochar Nanoparticles (BCNPs) are generated in the environment as a result of the weathering and degradation of bulk pyrolytic carbon (often called biochar). Nevertheless, the recent development of bulk biochar application as heavy metal sorbents contributes to the abundance amount of BCNPs in the environment. The diverse sources of biomass and pyrolysis methods applied during biochar production profoundly impact the physicochemical properties of BCNPs and their fate and transport in the environment. This research aims to characterize the surface reactivity of BCNPs from mixed wood chips and observe their impacts on Bacillus subtilis, a common Gram-positive; a wide range of natural environment-bacterium, in the presence and absence of a potentially toxic monovalent metal, cadmium (Cd). Experiments were conducted by pyrolyzing mixed wood chips, a common biochar feedstock, at 500oC and BCNPs extracted via sonication in water from the resulting bulk biochar. The BCNPs surface reactivity analysis was conducted through potentiometric titration. Furthermore, Bacillus subtilis cells were exposed to systems containing Cd, BCNPs, or Cd+BCNPs at several different treatment levels. Toxicity tests to investigate growth inhibition of Bacillus subtilis were conducted using the Mueller-Hinton Agar (MHA). The results show that BCNPs are effective sorbents for Cd removal, in line with their elevated surface reactivity and surface area. However, due to their small size and mobility, BNCPs act as a transport vector for contaminants in soils and water. In addition, this study found that the interaction between BCNPs and microorganisms can be treated and tested according to methods for generic nanoparticles in the environment. Further mRNA analyses of Bacillus subtilis will be beneficial to gain a comprehensive understanding of how BCNPs with and without Cd impact microorganisms in the environment.

Understanding the impacts of biochar nanoparticles (BCNPs) on the speciation and toxicity of Cd toward Bacillus subtilis

ACS Spring 2022

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