Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations...Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations in pool water and reduce the microbial risk, higher chlorine doses are required during disinfection. Unfortunately, this process produces carcinogenic disinfection byproducts that increase the risk of chemical exposure. Therefore, quantitatively evaluating the comparative microbial vs. chemical exposure risks that stem from chlorination inactivation of Giardia in swimming pool water is an issue that demands attention. We simulated an indoor swimming pool disinfection scenario that followed common real-world disinfection practices. A quantitative microbial risk assessment coupled with a chemical exposure risk assessment was employed to compare the Giardia microbial exposure risk(MER) and the trihalomethane chemical exposure risk(CER) to humans. The results demonstrated a 22% decrease in MER-and CER-induced health exposure risk, from 8.45E-5 at 8:00 to 6.60E-5 at 19:00. Both the MER and CER decreased gradually, dropping to 3.26E-5 and 3.35E-5 at 19:00, respectively. However, the CER exceeded the MER after 18:30 and became the dominant factor affecting the total exposure risk. Past the 18 hr mark, the contribution of trihalomethane CER far exceeded the risk aversion from microbial inactivation, leading to a net increase in total exposure risk despite the declining MER. Swimmers may consider swimming after 19:00, when the total exposure risk is the lowest. Lowering water temperature and/or p H were identified as the most sensitive factors to minimize the overall health exposure risk.展开更多
Residual enrofloxacin(ENR)exposed in aqueous environments is challenging to the ecosphere.In this work,a layered double hydroxide CoAl-LDH was used to activate the common oxidizing agent persulfate(PS)for photodegrada...Residual enrofloxacin(ENR)exposed in aqueous environments is challenging to the ecosphere.In this work,a layered double hydroxide CoAl-LDH was used to activate the common oxidizing agent persulfate(PS)for photodegradation of ENR,and the degradation pathways of ENR were scrutinized and elucidated.The results indicated that,under the optimal conditions obtained through orthogonal experiments,even though the degradation rate of ENR was as high as 97.72%,the removal of total organic carbon(TOC)from the system was only about 30%.Eleven probable reaction pathways were categorized,and thirty-one types of intermediates were identified in participating in the complex degradation process.The major products of ENR were P4(C_(17)H_(20)FN_(3)O_(3)),P22(C_(19)H_(22)FN_(3)O_(4)),P19(C_(17)H_(18)FN_(3)O_(3)),which are mainly derived from the cleavage of the piperazine groups and quinolone rings.Density functional theory(DFT)calculations of the Fukui index for ENR revealed that the two N atoms in the piperazine ring were the core reactive sites in triggering the degradation chains,which were sensitive for electrophilic attack by the dominant radicals(·OH and SO_(4)·^(-))generated from the composite PS-UV-CoAl-LDH system.展开更多
基金supported by the National Natural Science Foundation of China (No. 52000184)the Guangzhou Basic and Applied Basic Research Project (No. 202102020457)the Guangdong Basic and Applied Basic Research Foundation (No. 2019B1515120052)。
文摘Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations in pool water and reduce the microbial risk, higher chlorine doses are required during disinfection. Unfortunately, this process produces carcinogenic disinfection byproducts that increase the risk of chemical exposure. Therefore, quantitatively evaluating the comparative microbial vs. chemical exposure risks that stem from chlorination inactivation of Giardia in swimming pool water is an issue that demands attention. We simulated an indoor swimming pool disinfection scenario that followed common real-world disinfection practices. A quantitative microbial risk assessment coupled with a chemical exposure risk assessment was employed to compare the Giardia microbial exposure risk(MER) and the trihalomethane chemical exposure risk(CER) to humans. The results demonstrated a 22% decrease in MER-and CER-induced health exposure risk, from 8.45E-5 at 8:00 to 6.60E-5 at 19:00. Both the MER and CER decreased gradually, dropping to 3.26E-5 and 3.35E-5 at 19:00, respectively. However, the CER exceeded the MER after 18:30 and became the dominant factor affecting the total exposure risk. Past the 18 hr mark, the contribution of trihalomethane CER far exceeded the risk aversion from microbial inactivation, leading to a net increase in total exposure risk despite the declining MER. Swimmers may consider swimming after 19:00, when the total exposure risk is the lowest. Lowering water temperature and/or p H were identified as the most sensitive factors to minimize the overall health exposure risk.
基金support from the National Key Research and Development Program of China(2022YFE0104900)Foshan Shunde District Core Technology Breakthrough Project(2230218004273)+1 种基金2022 Zhuhai Social Development Science and Technology Program Project(2220004000355)Guangdong Basic and Applied Basic Research Foundation(2023B1515040028).
文摘Residual enrofloxacin(ENR)exposed in aqueous environments is challenging to the ecosphere.In this work,a layered double hydroxide CoAl-LDH was used to activate the common oxidizing agent persulfate(PS)for photodegradation of ENR,and the degradation pathways of ENR were scrutinized and elucidated.The results indicated that,under the optimal conditions obtained through orthogonal experiments,even though the degradation rate of ENR was as high as 97.72%,the removal of total organic carbon(TOC)from the system was only about 30%.Eleven probable reaction pathways were categorized,and thirty-one types of intermediates were identified in participating in the complex degradation process.The major products of ENR were P4(C_(17)H_(20)FN_(3)O_(3)),P22(C_(19)H_(22)FN_(3)O_(4)),P19(C_(17)H_(18)FN_(3)O_(3)),which are mainly derived from the cleavage of the piperazine groups and quinolone rings.Density functional theory(DFT)calculations of the Fukui index for ENR revealed that the two N atoms in the piperazine ring were the core reactive sites in triggering the degradation chains,which were sensitive for electrophilic attack by the dominant radicals(·OH and SO_(4)·^(-))generated from the composite PS-UV-CoAl-LDH system.
