Inhibitory Effects of Aquadag, a Black Carbon Surrogate, on Microbial Growth via Surface-Mediated Stress: Evidence from Adenosine Triphosphate Assay

Black carbon (BC) from incomplete combustion sources including traffic emissions affects human health due to its physical characteristics and ubiquity in urban environments. We examined the effects of BC on microbial growth in the presence of particulate matter (PM), using Aquadag as a surrogate for BC. Brunauer-Emmett-Teller analysis showed BC had a specific surface area of 123.2 m² g^-1, with over 90% of particles smaller than 100 nm, indicating strong surface interaction potential. Pseudomonas aeruginosa PA14 was cultured for 7 days with various BC concentrations and fixed PM. Increasing BC (0-100 ng mL^-1) significantly inhibited growth, evidenced by a decline in cellular adenosine triphosphate (cATP) with a slope of -1.296 ± 0.258 cATP ng mL^-1/BC ng mL^-1. The seven-day mean cATP slope ranged from 77 to 131, with control at 161. The biomass stress index (BSI) increased by 56%, rising from 28.6 ± 8.8% (control) to 44.6 ± 16.1% under high BC. The BSI change was minimal on day 1 (<+0.1% per BC ng mL^-1) but greater on days 5 (+0.125 ± 0.052%) and 7 (+0.130 ± 0.075%). BC does not cause immediate microbial death, but prolonged exposure induces cumulative stress, damages synthetic enzymes, inhibits growth, and may lead to cell death, with potential public health implications.