Evaluation of Dioxins in Minnesota Lakes

PROJECT OVERVIEW
The antibacterial compound triclosan is present in many consumer products, including soaps, toothpastes, lotions, and deodorants. Wastewater treatment does not completely remove triclosan or its derivatives and so the chemicals are discharged into surface waters. Once present in surface waters, sunlight converts triclosan and its derivatives into dioxins, a class of chemicals that are known to be toxic, carcinogenic, and persistent and accumulative in sediment and fish. Researchers at the University of Minnesota's Department of Civil Engineering are using this appropriation to study sediment samples in order to determine the current and historic levels of dioxins in the water and how much is attributable to triclosan and its derivatives. Findings will be used to make recommendations on how water quality can be improved and protected in the future.

OVERALL PROJECT OUTCOME AND RESULTS
Triclosan is an antimicrobial agent in many consumer products such as liquid handsoaps, bar soaps, dishwashing liquid, deodorants, anti-gingivitis toothpaste, and acne creams. Because it is washed down the drain through the normal course of use, triclosan is commonly detected in wastewater effluent. During water and wastewater disinfection with chlorine, triclosan can be transformed to a series of chlorinated triclosan derivatives. When discharged into surface waters, triclosan and its derivatives react in sunlight to form a series of four polychlorinated dibenzo-p-dioxins. Dioxins are persistent organic pollutants that are toxic, carcinogenic, and endocrine disrupting. Thus, dioxins pose a risk to the health of aquatic species and their predators (including humans).

To evaluate the historical and current exposure of surface waters to triclosan, chlorinated triclosan derivatives, and their derived dioxins, sediment cores were collected from wastewater-impacted Minnesota lakes. Following radiometric dating, triclosan and chlorinated triclosan derivatives were extracted from core sections and quantified. Dioxins were extracted from the same core sections and also quantified.

The concentrations and temporal trends of triclosan, chlorinated triclosan derivatives, and their dioxins in aquatic sediments were found to be a function of historical wastewater treatment operations and lake system scale. Cores collected from large-scale riverine systems with many wastewater sources recorded increasing concentrations of triclosan, chlorinated triclosan derivatives, and their derived dioxins since the patent of triclosan in 1964. The trends were directly attributed to increased triclosan use, local improvements in treatment, and changes in wastewater disinfection practices. Concentrations of triclosan, chlorinated triclosan derivatives, and their dioxins were higher in small-scale systems, reflecting a greater degree of wastewater impact. In a lake receiving no wastewater influent, no triclosan was detected. Low levels of the four triclosan-derived dioxins were found in northern wastewater-impacted Minnesota lakes prior to the introduction of triclosan as well as in the lake with no wastewater input. The background levels of these dioxins were attributed to a secondary, region-specific source. Nonetheless, it is clear that triclosan is the major source of these dioxins after 1960. The contribution of the triclosan-derived dioxins to the total dioxin pool in terms of mass was determined for each sediment core. In heavily impacted systems, the dioxin contribution from triclosan and chlorinated triclosan derivatives accounted for up to 60% of total dioxin mass in recent sediment. Thus, the discharge of triclosan and chlorinated triclosan derivatives may pose a threat to wastewater-impacted lakes.

The findings of this work suggest that additional treatment of wastewater to remove triclosan, additional regulation of triclosan use, or dissemination of information regarding the prevalence of triclosan in consumer products may be necessary. Full results are presented in the M.S. Thesis of Cale T. Anger submitted with this report.

PROJECT RESULTS USE AND DISSEMINATION
This project led to the production of the M.S. Thesis of Cale T. Anger, Quantification of Triclosan, Chlorinated Triclosan Derivatives, and their Dioxin Photoproducts in Lacustrine Sediment Cores. The thesis received the Distinguished Master's Thesis Award from the University of Minnesota, recognizing it as the best thesis at the U of MN for 2011-2012. A manuscript with the same title has been submitted the peer reviewed journal Enviornmental Science & Technology. The results of the work have been presented at the American Chemical Society National Meeting, the St. Croix River Research Rendevous, the Itasca Water Legacy Project lecture series, and the Mississippi River Forum. Two more presentations at the American Society of Limnology and Oceangraphy and the IWA Micropol and Ecohazard conferences are planned. We anticipate press coverage of the findings upon publication of the peer-reviewed article.