Document Detail

Aquatic photodegradation of sunscreen agent p-aminobenzoic acid in the presence of dissolved organic matter.
MedLine Citation:
PMID:  23084339     Owner:  NLM     Status:  Publisher    
Dissolved organic matter (DOM) is an important photosensitizer for the phototransformation of organic contaminants in sunlit natural waters. This article focuses on the photolysis kinetics and mechanism of sunscreen agent p-aminobenzoic acid (PABA) in the presence of four kinds of DOM; Suwannee River fulvic acid (SRFA), Suwannee River humic acid (SRHA), Nordic Lake fulvic acid (NOFA) and Nordic Lake humic acid (NOHA). It is evident that direct photolysis of PABA is highly pH-dependent because different species of PABA have different electrical densities on the ring system. The presence of four kinds of DOM inhibits the photolysis of PABA primarily due to their light screening effect. Meanwhile, a complex interaction involving energy transfer, triplet carbonyl group induced electron transfer, and amino acid induced proton abstraction between PABA and DOM is verified by competition kinetics experiments and density functional theory (DFT) computation. In addition, DOM-induced singlet oxygen ((1)O(2)) and hydroxyl radical (OH) are determined to play an insignificant role in PABA photolysis by competition dynamics method. Photoproducts identification using solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) techniques reveals that the distribution of the photoproducts could not be affected by the addition of DOM. Two photodegradation pathways of PABA are temporarily proposed, in which the di(tri)-polymerization of intermediates are the dominant pathway whereas the oxidation of amino group to nitryl followed by hydroxylation is a minor process. Our findings reveal that direct photolysis is the dominant transformation pathway of PABA in natural sunlit waters, while the presence of DOM could evidently influence such process by light screening effect, energy transfer, electron transfer and proton abstraction mechanism. The findings in this study provide useful information for understanding of interaction between DOM and organic contaminants.
Lei Zhou; Yuefei Ji; Chao Zeng; Ya Zhang; Zunyao Wang; Xi Yang
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-4
Journal Detail:
Title:  Water research     Volume:  -     ISSN:  1879-2448     ISO Abbreviation:  Water Res.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-22     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0105072     Medline TA:  Water Res     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2012 Elsevier Ltd. All rights reserved.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210046, PR China.
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