Assessment on the occurrence and removal of Triclosan and Triclocarban from a wastewater treatment plant and their potential ecological risks

Abstract

Increasing use of triclosan (TCS) and triclocarban (TCC) from pharmaceutical and personal care products (PPCPs), personal care products (PCPs), and other industrial applications have resulted in their continuous release into the environment. This is due to their incomplete removal in treated wastewater, and from non–diffuse sources e.g., runoffs. In addition, industrial effluents also release other forms of pollutants into wastewater treatment plants (WWTPs) that are not readily biodegradable in conventional biological treatment plants. In this study, the occurrence and removal of TCS, TCC and other contaminants in the WWTP from domestic and industrial influent (Darvill WWTP, Pietermaritzburg, South Africa) were investigated. The target compounds TCS and TCC were quantitatively analysed using gas chromatography–mass spectrometry (GC–MS), and yielded the measured environmental concentrations (MECs). Conversely, other forms of pollutants were qualitatively assessed using GC–MS in selected ion monitoring (SIM) mode. Both target compounds were detected in the influent and effluent, and, at across different process units. Moreover, using the sales data for the major product sources of TCS and TCC feeding the Darvill WWTP, predicted environmental concentrations (PEC) of the target compounds were determined. Risk quotients (RQs) were calculated to predict the likely risks of both chemicals in the wastewater, freshwater, and soil environmental matrixes. The MECs obtained for TCS were in the µg/L range, and the highest in the influent in the ranges of 1.02– 3.4 µg/L; whereas in the final effluent (after chlorination) detected values were <LOD–1.1 µg/L. Lower concentrations of TCC levels of two- to three-folds were measured as 0.45–1.1 µg/L and LOD–0.58 µg/L in the effluent (before chlorination) and final effluent (after chlorination), respectively. And, the concentrations showed variability across different treatment processes. The overall removal efficiency was 59% and 45% for TCS and TCC, respectively. Generally, TCS concentrations were higher than TCC concentrations from all treatment units assessed. Other pollutants detected in the influent and effluent were diisoprophylnaphthalenes (DIPNs), 2–Heptyl–4–phenyl–1,3–dioxolane, and polychlorinated biphenyls (PCBs) – hence providing evidence of industrial influent into the Darvill WWTP as these chemicals are mostly used in industrial processes. Four transformation products (TPs) of TCS and TCC were detected, namely; methyl triclosan (MeTCS), 2,4–dichlorophenol (2,4–DCP), non–chloro carbanilide (NCC), and 4–chloroanaline (4–CA). 2,4–DCP and NCC were detected in all samples analysed at concentration ranges of 0.26–0.4 µg/L and 1.13–2.02 µg/L, respectively. However, MeTCS and 4–CA were not detected above limit of detection in all samples analysed. The formation of TPs, however, was not exclusively due to the TCS and TCC biodegradation along the WWTP alone. This is because both 2,4–DCP and NCC were successfully detected in the influent stream. The modelled PECs were in good agreement with MECs with average PEC/MEC ratios of 1 and 3 for TCS and TCC, respectively. Hence, indicative of reliability of using PECs as a practical approach to quantify the concentrations of contaminants from household products in the aquatic environment. TCS and TCC RQs for microorganisms were > 1 and < 1, respectively, suggesting possible negative impact of the former to the performance of biological wastewater treatment plants. Results of TCS and TCC showed potential risks to freshwater species irrespective of the tropic level of focus (algae, crustacean, and fish) with RQs obtained exceeding 1. RQ results in terrestrial system were all < 1, indicating low or no risks. All these results taken together, calls for the protection of the freshwater systems by banning incorporation of TCS in products as has been done in other jurisdictions including the USA, European Union, and Canada.