A Study of Photoinduced Toxicity of 1-Aminopyrene (1-AP) to Microbial Assemblages and the Effect of Humic Substances on 1-AP Photolysis.

Two sources of humic acid (HA) were added to a phosphate-buffered solution to determine the effect of HA on 1-aminopyrene (1-AP) photolysis rate under UV-A irradiation and natural solar irradiation. Microbial assemblages in a river water sample were used to determine the ecotoxicity of 1-AP and its photoproducts. The microbial bioassay includes spread plate counting and microbial mineralization of 14 C-D-glucose, succinate, and citrate. At 1-AP concentration of 8 μM, bacterial viability was not affected and heterotrophic activities were inhibited by 41% to 63% after exposure for 24 hr. Exposure to 1-AP photoproducts inhibited bacterial viability and heterotrophic activities by 58% and 77% to 84%, respectively. Therefore, photoinduced toxicity of 1-AP to microbial assemblages was observed in this study. With additions of HA at concentrations of 10-80 ppm, the photolysis rate constants of 1-AP (10 μM) in phosphate-buffered (pH 7.0; 1 mM) solutions were enhanced by up to fivefold. The magnitude of the enhancement depends on the type and concentration of HA. Under irradiation from both sources, photoysis rate of 1-AP was four to five times higher in the river water than that in phosphate-buffered solution. The enhancement is assumed to be the result of sensitization by HA present in the river water. [ABSTRACT FROM AUTHOR]