Solar/Chlorination Transformation And Toxicity Studies Of UV Filter Diethylamino Hydroxybenzoyl Hexyl Benzoate

Diethylamino Hydroxybenzoyl Hexyl Benzoate（DHHB）,a type of UV filter,can be found in sunscreens and other personal care products.Due to the large number of applications that make it abundant in the environment,it is necessary to study the environmental behaviour of DHHB because of its photostability,lipid solubility and the fact that it has not been studied whether it has any negative environmental effects.DHHB can be introduced into swimming pools by swimmers.In outdoor pools,DHHB will inevitably interact with active chlorine and sunlight.Therefore,the present work is dedicated to the mechanism,products and environmental and health risk of photodegradation,chlorination and solar/chlorination of DHHB.The details of the study and the conclusions are as follows:（1）The degradation rate of DHHB under photodegradation conditions was slow,the aqueous matrix Cl^-and HCO₃^-inhibited the photodegradation due to light diminishing effect and p H increase to reduce the generation of active species,respectively.NO₃^-and dissolved organic matter（DOM）promoted the degradation of DHHB due to the generation of active species by light absorption,and Br^-,NH₄⁺and urea did not affect the photodegradation of DHHB.Compared with photodegradation,the degradation rate of DHHB in chlorination process was faster,with a second order rate constant of 207±11 M^-1 s^-1 for DHHB with active chlorine in a buffer solution system containing 3 mg/L active chlorine,Cl^-,HCO₃^-,NH₄⁺,DOM and low concentration of urea inhibited the chlorination degradation of DHHB due to reduction of active chlorine,the change of active chlorine form in the solution due to the increase of p H,the conversion of chloride ions into less oxidising substances and the consumption of active chlorine,respectively,Br^-promoted the degradation due to the reaction with active chlorine to generate active bromine,and NO₃^-shows no effect.（2）The mechanism of solar/chlorination process was investigated by adding free radical quencher.It was found that active chlorine contributed 85%to the degradation of DHHB during Solar/chlorination process,while^·OH and active chlorine radical species(RCS,i.e.,Cl O^·,Cl^·,Cl₂^·-)degraded only 15%of DHHB.UV/H₂O₂ experiments indicated that the reaction rate of^·OH with DHHB was 3.88×10⁶ M^-1s^-1 higher than that of active chlorine with DHHB at 207±11 M^-1 s^-1,so the fact that only 15%of DHHB was degraded by the active species during DHHB solar/Chlorination process was due to the low free radical production.During DHHB solar/Chlorination process,Cl^-,high concentrations of HCO₃^-,NH₄⁺,and DOM exhibited inhibitory effects on the degradation of DHHB due to light shielding effect,reduced generation of active species,or quenching of active species,while Br^-and NO₃^-exhibited some promoting effects due to the generation of more oxidising or more active species.（3）Seven possible transformation by-products（TBPs）were identified including mono-,dichlorinated,dealkylated,and monochlorohydroxylated transformation by-products.Four degradation pathways,chlorine substitution,structural rearrangement and dealkylation at the tert-amino group were proposed for the transformation of DHHB in the solar/Chlorination process.（4）The results of the in silico method and the risk assessment of the DHHB and the TBPs suggested that the chlorinated by-products of DHHB are more toxic,both DHHB and its chlorinated byproducts may pose a significant health risk,the Aliivibrio fischeri toxicity test confirmed this conclusion.