Fate of triclosan and evidence for reductive dechlorination of triclocarban in estuarine sediments

Abstract

The biocides triclosan and triclocarban are wastewater contaminants whose occurrence and fate in estuarine sediments remain unexplored. We examined contaminant profiles in 137Cs/7Be-dated sediment cores taken near wastewater treatment plants in the Chesapeake Bay watershed (CB), Maryland and Jamaica Bay(JB), New York. In JB, biocide occurrences tracked the time course of biocide usage and wastewater treatment strategies employed, first appearing in the 1950s (triclocarban) and 1960s (triclosan), and peaking in the late 1960s and 1970s (24 +/- 0.54 and 0.8 +/- 0.4 mg/kg dry weight, respectively). In CB, where the time of sediment accumulation was not as well constrained by 137Cs depth profiles, triclocarban was only measurable in 137Cs-bearing sediments, peaking at 3.6 +/- 0.6 mg/ kg midway through the core and exceeding 1 mg/kg in recent deposits. In contrast, triclosan concentrations were low or not detectable in the CB core. Analysis of CB sediment by tandem mass spectrometry produced the first evidence for complete sequential dechlorination of triclocarban to the transformation products dichloro-, monochloro-, and unsubstituted carbanilide, which were detected at maxima of 15.5 +/- 1.8, 4.1 +/- 2.4, and 0.5 +/- 0.1 mg/kg, respectively. Concentrations of all carbanilide congeners combined were correlated with heavy metals (R2 > 0.64, P < 0.01), thereby identifying wastewater as the principal pathway of contamination. Environmental persistence over the past 40 years was observed for triclosan and triclocarban in JB, and for triclocarban's diphenylurea backbone in CB sediments.

Figure 1

Map of the U.S. East Coast showing sampling locations in a tributary to the Chesapeake Bay, MD, and in a deep estuarine basin in Jamaica Bay, NY. A close-up view of MD shows 8 sites of sampling for surface sediment (0 – 10 cm depth) taken along a cross section beginning 450 m inland to 5700 m (arrow) seaward relative to the wastewater outfall.

Figure 2

Depth-time profile of TCS and TCC in sediment from Jamaica Bay and Chesapeake Bay estuarine sampling locations. Open symbols indicate values below the detection limit and filled symbols with an asterisk indicate that the analyte was detected, but its concentration was below the LOQ. Note that the TCS scale is on the upper x- axis and the TCC scale is on the lower x- axis. Arrows on the JB plot indicate patent issuance dates for TCS (1964) and TCC (1957), that ushered in chemical mass production. Error bars indicate the standard deviation of analyte concentrations in two or more replicate extractions of the same sediment section.

Figure 3

Depth-time profile of TCC and its postulated products of complete sequential dechlorination in sediment cores taken from the Chesapeake Bay, MD and Jamaica Bay, NY. Open symbols indicate values below the detection limit. In JB16, the dechlorination products DCC, MCC and NCC were measured in a single extract from each sediment section and for all other data points error bars are the average and standard deviation of measurements of two or more sediment extracts from each sediment section. For comparison the units on the upper axis are in molarity and bottom axis in mg/kg. TCC appears to be recalcitrant in Jamaica Bay sediment, whereas Chesapeake Bay sediment shows evidence of TCC dechlorination in deep sediment layers.