Photolysis Mechanism Of Typical Preservative Parabens And Their Consequences For Evolution Of Human Estrogen Effect

Due to the widespread occurrence of emerging organic contaminants?EOCs?in water,there is great attention paid to their environmental behaviors and adverse effects on human health.Preservative parabens?PBs?are an important group of EOCs in aquatic environment.Toxicological studies have shown that PBs are potential exogenous estrogen,which could interfere with the endocrine system,causing a series of adverse health effects.Therefore,in this paper,ethyl paraben?EP?and butyl paraben?BP?were selected as the targeted pollutants to systematically study their degradation mechanism,kinetics and the human estrogenic activity during UV photolysis.The thesis mainly obtains the important results on the following aspects:First,using a typical short chain preservative EP as an example,the evolution of estrogenic activity during photochemical degradation in water was investigated.The results show that 500?M EP can be completely removed under UV irradiation within 90 min.The degradation rate constant was 0.067 min^-1.The estrogenic activity initially increased and then decreased,with maximum estrogenic activity at 40 min of UV irradiation while the degradation efficiency reached 40±10%.The increased estrogenic activity during photochemical degradation was due to the formation of photochemically generated oligomers,[4-Hydroxy-isophthalic acid 1-ethyl ester 3-?4-hydroxy-phenyl?]and4-Hydroxy-3-[2-?4-hydroxy-phenoxycarbonyl?-ethyl]-benzoic acid ethyl ester,instead of the expected OH-adducts.The EC₅₀ value of OH-adducts 3,4-Dihydroxy-benzoic acid ethyl ester?3-OH-EP?was about an order of magnitude higher than that of EP.This finding implies the lower estrogenic activity of OH-adduct as compared to the original EP,and this conclusion breaks people's traditional perception.Furthermore,the triplet excited state?³EP*?was found to be the main reactive species from both quenching experiments and laser flash photolysis results.Based on the identification of degradation intermediates and theoretical chemical calculation,the possible photochemical degradation mechanism of EP was tentatively proposed.Considering the effect of the length in alkyl chain on PBs photodegradation,BP was selected for further investigation.The results show that 100?M BP was found to be completely removed under UV irradiation within 120 min.The degradation rate constant was0.042 min^-1 and the mineralization rate was 20%.The triplet excited state?³BP*?was found to be the main reactive species from quenching experiments rather than hydroxyl radicals.It was inferred that ³BP*directly reacted with O₂to form a complex intermediate?internal peroxide?,then led to the main formation of 3,4-Dihydroxy-benzoic acid butyl ester?3-OH-BP?.The EC₅₀ value of 3-OH-BP was an order of magnitude higher than that of original BP,indicating the estrogenic activity of BP is higher than 3-OH-BP.The estrogenic activity continued to decrease during the process of photochemical degradation.Moreover,we found that there was absent of dimers products with estrogenic activity during the degradation of higher concentrations of BP.Thus,it can be concluded that the estrogenic activity can't be overlooked during the degradation of BP,although the BP degradation product imposes the decreased the estrogenic activity as compared with the original BP.The obtained findings suggest that the environmental and health impact of degradation products together with the original parent PBs should be paid more attention in future studies and risk assessments.