Upon entering USGS national data on TCS (35) into the forecasting algorithm, TCC emerged in 2005 as a previously unrecognized CEC that had been overlooked by environmental analysts for almost half a century it was predicted to rank in the top 10 CECs in occurrence rate and in the top 20 in maximum concentration among 96 water pollutants. (8) Significant co-occurrence of TCC and TCS ( R 2 = 0.988) can be easily understood from their similar uses, chemical structures, and down-the-drain disposal mode. (39) When applied to the cityвЂ™s groundwater, drinking water, wastewater, and sewage sludge, TCC was detected in many of these matrices and consistently in samples also containing TCS. (39) Use of this tool on samples from Baltimore, Maryland, showed the presence of TCC in every urban stream monitored. (38) Relief from this conundrum arrived in 2004 with a simple LC-MS technique allowing direct detection of underivatized TCC. For TCC to travel through a standard GC column and be detected, its reactive groups first need to be derivatized. Contrary to TCS, TCC cannot be analyzed by standard GC methods, thereby concealing for decades TCCвЂ™s presence in environmental samples acquired, extracted and analyzed for the occurrence of anthropogenic pollutants. Triclocarban-a fungicide and bacteriostat with activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) (37)-emerged as a contaminant of emerging concern (CEC) much later, enabled by LC-MS rather than GC-MS detection techniques. (13) Today, these numbers may be even higher. In 1999/2000, TCS or TCC were present in 75% of liquid soaps and 29% of bar soaps in the U.S. supermarket shelves, likely bring home a product containing either TCS or TCC. Consumers reaching for a random soap on U.S. (12) By contrast, TCC sees far more limited applications, mostly in bar soap formulated to concentrations of about 2% by weight, higher than the 0.1вЂ“0.5% content of TCS-enabled antimicrobial products. (9, 11) Despite labeling requirements, consumer awareness of harmful active ingredients in household products remains low. This multibillion dollar market has saturated supermarkets worldwide and vastly accelerated the consumption of antimicrobial products today, TCC and more so TCS can be found in soaps, detergents, clothing, carpets, paints, plastics, toys, school supplies, and even in pacifiers, with over 2000 antimicrobial products available in 2014вЂs $1.4 billion U.S. and abroad over the past two decades, due to relaxed regulation, aggressive and widespread advertising, and media reports driving fears of potent and sometimes lethal microbial infections acquired in everyday-life by unsuspecting victims. Indeed, the consumption of TCS and TCC and the abundance of antimicrobial products have increased in the U.S. (6, 7) Curiously, triclocarban (TCC) and triclosan (TCS), two persistent antimicrobials first introduced to commerce in 19, respectively, (8) feature a very similar chemistry (i.e., two benzene rings carrying multiple chlorines) yet continue to be produced and consumed to this day at high volume.

(1, 4) For example, hexachlorophene, introduced in 1948 as a binuclear aromatic organohalide carrying six chlorine substituents, (5) was banned from most uses by the 1970s. However, within a few years, many of these compounds and formulations showed adverse effects, including human toxicity, ecotoxicity, and unwanted environmental persistence and bioaccumulation, quickly leading to regulatory bans and phase-outs. (1) The resultant synthetic organohalides, which are either absent or rare in natural environments, (2, 3) immediately were put to large volume, worldwide use as biocides. In the late 1930s and early 1940s, it was discovered that the substitution on aromatic rings of hydrogen atoms with chlorine, yielded a novel chemistry of powerful biocides, including antimicrobials.

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