TOXICITY OF SILVER NANOPARTICLES TO ACHROMOBACTER DENITRIFICANS

The indoor culture method was selected to study the toxic mechanism of AgNPs to Achromobacter denitrificans and the effects of silver nanoparticles on the growth inhibition, ammoniation, assimilation and absorption of NH₄⁺-N, cell membrane surface structure and the accumulation of the reactive oxygen species. The study found that AgNPs could inhibit bacterial growth, and the inhibitory effect was positively related to concentration and exposure time. In the nitrification medium supplemented with 10 mg/LAgNPs, the growth inhibition rate of Achromobacter denitrificans reached 38.2% after 12 h, while the growth inhibition rate was only 11.5% when 1 mg/LAgNPs was added. Under different AgNPs exposure concentrations, the growth inhibition rates tended to be stable after 4~6 h. The biochemical activity of bacteria after exposure to AgNPs decreased. When the dosage of AgNPs increased from 1 mg/L to 10 mg/L, the NH⁺₄-N generation rate decreased by 25.3%, from 2.77 mg/(L·h) to 2.07 mg/(L·h); NH₄⁺-N assimilation rate decreased by 69.1%, from 5.52 mg/(L·h) to 1.71 mg/(L·h). Besides, pH was an important factor affecting the toxicity. Both weak acid(pH=5.0) and weak alkaline(pH=9.0) were not conducive to bacterial survival. Through the analysis of the mechanism of toxicity, we found that AgNPs can cause the depression and rupture of the cell membrane surface, the leakage of substances in the membrane, and the accumulation of reactive oxygen species in the cells.