Effects of riboflavin photoproducts on microbial activity during photosensitization of atrazine transformation.
The contributions and effects of photolysis and microbial assemblages to 37.6 mg/L riboflavin-sensitized atrazine transformation were studied along with the toxicity of the intermediate mixtures. High-performance liquid chromatography analysis revealed that riboflavin significantly enhanced the phototransformation of atrazine (10 mg/L) by reducing the parent compound concentration to less than 20% in 72 h. However, radiotracer measurements indicated atrazine was not mineralized to the same degree after 3 days of exposure. We hypothesize that riboflavin-sensitized transformation of atrazine is primarily photochemical; however, the biological component seems to promote overall atrazine degradation under solar irradiation. Based on the results of spread plate counting or 14C-glucose mineralization measurement, at a test concentration of 12.1 mg/L, lumichrome (a major riboflavin photoproduct) was found to be nontoxic to the test microbial assemblages in a reservoir water sample. Other riboflavin photoproducts and/or certain chemically reactive species were speculated to cause a cytotoxic effect. Overall, our data indicate that riboflavin may be an economical photosensitizing agent for atrazine degradation, but the apparent photoinduced cytotoxicity observed during transformation is of concern to the microbial assemblages that are needed for complete remediation. Further investigation into why the biotic component enhances riboflavin phototransformation of atrazine and the time frame of microbial recovery from riboflavin inhibition is needed. Such work may lead to cost-effective surface water treatment systems involving combined photochemical and microbial degradation processes.
Glover
Hollis
H
Department of Biology, Jackson State University, Jackson, Mississippi 39217, USA.
Hwang
Huey-Min
HM
Zeng
Kui
K
D001280:Atrazine / Q000378:metabolism*; D001673:Biodegradation, Environmental; D006540:Herbicides / Q000378:metabolism*; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology*; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000378:metabolism*
D006540:Herbicides; D017319:Photosensitizing Agents; D014874:Water Pollutants, Chemical; D001280:Atrazine; D012256:Riboflavin