Abstract
Antimicrobial compounds are used in a broad range of personal care, consumer and healthcare products and are frequently encountered in modern life. The use of these compounds is being reexamined as their safety, effectiveness and necessity are increasingly being questioned by regulators and consumers alike. Wastewater often contains significant amounts of these chemicals, much of which ends up being released into the environment as existing wastewater and sludge treatment processes are simply not designed to treat many of these contaminants. Furthermore, many biotic and abiotic processes during wastewater treatment can generate significant quantities of potentially toxic and persistent antimicrobial metabolites and byproducts, many of which may be even more concerning than their parent antimicrobials. This review article explores the occurrence and fate of two of the most common legacy antimicrobials, triclosan and triclocarban, their metabolites/byproducts during wastewater and sludge treatment and their potential impacts on the environment. This article also explores the fate and transformation of emerging alternative antimicrobials and addresses some of the growing concerns regarding these compounds. This is becoming increasingly important as consumers and regulators alike shift away from legacy antimicrobials to alternative chemicals which may have similar environmental and human health concerns.
Highlights
TCS: triclosan; Wastewater treatment plants (WWTPs): wastewater treatment plant; BNR: biological nutrient removal; MeTCS: methyl triclosan; dw: dry weight; n/a: data not avaiable; LOD: limit of detection; 2,4-DCP: 2,4-dichlorophenol; 2,3,4-TCP: 2,3,4-trichlorophenol; DCDD: dichlorodibenzo-p-dioxins; TH-AD: CambiTM thermal hydrolysis followed by anaerobic digestion; TCS-SO4: triclosan sulfate; TCS-gluc: glucuronidated triclosan; SRTs: solids retention times; MH: mesophilic; TH: thermophilic; LOQ: limit of quantification
The degradation pathway of TCC by a pure bacterium Sphingomonas sp. strain YL-JM2C, which was isolated from activated sludge of a WWTP in Xiamen (China), was studied by Mulla et al [170]
Legacy antimicrobials have been a fixture of modern life for over 40 years
Summary
Emerging contaminants consist of wide-ranging and expanding classes of anthropogenic and naturally occurring unregulated substances, on the occurrence, behavior, environmental fate and toxicity of which there are limited data [1,2,3]. TCS: triclosan; WWTP: wastewater treatment plant; BNR: biological nutrient removal; MeTCS: methyl triclosan; dw: dry weight; n/a: data not avaiable; LOD: limit of detection; 2,4-DCP: 2,4-dichlorophenol; 2,3,4-TCP: 2,3,4-trichlorophenol; DCDD: dichlorodibenzo-p-dioxins; TH-AD: CambiTM thermal hydrolysis followed by anaerobic digestion; TCS-SO4: triclosan sulfate; TCS-gluc: glucuronidated triclosan; SRTs: solids retention times; MH: mesophilic; TH: thermophilic; LOQ: limit of quantification. Digesters were operated at SRTs of 6, 12 and 20 days (corresponding to an organic loading rate (OLR) range from 1.46 to 5.25 g volatile solids (VS)/L/day) and showed less of an increase in TCS concentration (in terms of μg/g dw) in thermophilic versus mesophilic digesters This agrees with results from full-scale mesophilic anaerobic digesters (~35 ◦C, ~21-day SRT) in Saskatchewan, Canada, which utilized mixed primary and secondary BNR sludge [43]. The direct impacts of TCS are becoming better understood, further work is urgently needed to better understand the potential impacts of its conjugates and degradation products and their fates in the environment
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