Humic Substance Effect on Photochemical Fate of PAHs

Jackson State University, Jackson MS

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Abstract

The aquatic photolysis of polycyclic aromatic hydrocarbons (PAHs) can be influenced in several ways by the human substances (HS) present in natural waters. On one hand, direct photolysis can be inhibited because of the competitive absorption by colored HS as a light filter. This may lead to decrease in the photolysis rates in the presence of HS compared to the reactions in pure water. On the other hand, UV also induces a variety of photochemical changes in dissolved organic carbons (including humic acid, HA and fulvic acid, FA) and PAHs and lead to production of reactive oxygen species and PAHs in natural aquatic environments may differ significantly from those present in pure water. In this proposed research, we will determine the kinetics of photodegradation of selected PAHs in natural waters as well as in buffered distilled water with and without HS. HA and FA materials will be obtained from commercial source and self-extracted sources. The effect of HS on the persistence, toxicity and degradation pathways of the candidate compounds will be determined. The mechanism of PAHs photolysis in the presence of HA and FA will be studied through the identification of the photoproducts by using microbial bioassay-directed chemical fractionation approach. The influence of pH on the interaction between HS and PAHs will also be investigated in this study. Specifically, we will: (1) measure acute genotoxicity and ecotoxicity of selected PAHs with Mutatox PAHs with Mutatox Test, Microtox Test and other techniques such as respirometry and microbial heterotrophic uptake of glucose and thymidine in the presence of absence of HA and FA; (2) compare major species of the PAHs photoproducts in the presence and absence of HA and FA; (3) determine the effect of HS on bioremediation efficiency of PAHs with riboflavin (an environmentally friendly photosensitizer); (4) model the dependence of toxicity/inhibition index values (e.g., ED50 of Microtex Test and respirometric technique) in individual toxicity tests on HS concentrations; and (5) assess the effect of pH on the influence of HS on the photo-induced toxicity of PAHs. The hypotheses for this study are: (1) The humic substances can reduce availability of solar irradiation in surface waters; therefore, photo- induced toxicity of PAHs in natural aquatic environment will be lower than the counterpart in pure aqueous solutions; (2) With proper manipulation of pH, remediation of PAHs-contaminated waters can be successfully implemented. The Specific Aims of this project are: 1) To determine the influence of HS on photo-induced ecotoxicity and genotoxicity of selected PAHs in natural aquatic environments with microbial bioassays; (2) To determine the effect of humic substances on the persistence and degradation pathways of the candidate PAHs; (3) To study the influence of HS on the efficiency and health impact of using sensitized photolysis for treating PAHs-contaminated waters; (4) To determine the effect of pH on the influence of HS on photo-induced toxicity of PAHs. The long-term objectives are: (1) To enhance the research capability of JSU in th area of environmental health; and (2) To fulfill MBRS Program's mission to study the possible mechanisms by which PAHs compromise human health.