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Assessing the source-to-stream transport of benzotriazoles during rainfall and snowmelt in urban and agricultural watersheds Abha Parajulee, Ying Duan Lei, Amila O. DeSilva, Xiaoshu Cao, Carl P.J. Mitchell, and Frank Wania Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05638 • Publication Date (Web): 29 Mar 2017 Downloaded from http://pubs.acs.org on March 29, 2017
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Environmental Science & Technology
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Assessing the source-to-stream transport of benzotriazoles during rainfall and snowmelt in
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urban and agricultural watersheds
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Abha Parajulee1, Ying Duan Lei1, Amila O. De Silva2, Xiaoshu Cao1, Carl P. J. Mitchell1, Frank
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Wania1*
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Military Trail, Toronto Ontario, M1C 1A4
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2
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Lakeshore Road, Burlington, Ontario, Canada L7S 1A1
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Corresponding Author:
Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265
Water Science and Technology Directorate, Environment and Climate Change Canada, 867
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E-mail:
[email protected] 11
TOC/Abstract Art
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ABSTRACT
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While benzotriazoles (BTs) are ubiquitous in urban waters, their sources and transport remain
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poorly characterised. We aimed to elucidate the origin and hydrological pathways of BTs in
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Toronto, Canada, by quantifying three BTs, electrical conductivity, and δ18O in high-frequency
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stream-water samples taken during two rainfall and one snowmelt event in two watersheds with
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contrasting levels of urbanization. Average concentrations of total BTs [ΣBTs] were 4.8 to 84
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times higher in the more urbanized Mimico Creek watershed relative to the primarily agricultural
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and suburban Little Rouge Creek. Strong correlations between upstream density of major roads
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and total BT concentrations or BT composition within all events implicate vehicle fluids as the
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key source of BTs in both watersheds. Sustained historical releases of BTs within the Mimico
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Creek watershed have likely led to elevated [ΣBTs] in groundwater, with elevated concentrations
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observed during baseflow that are diluted by rainfall and surface runoff. In contrast, relatively
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constant concentrations, caused by mixing of equally contaminated baseflow and rainfall/surface
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runoff, are observed in the Little Rouge Creek throughout storm hydrographs, with an occasional
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first flush occurring at a sub-site draining suburban land. During snowmelt, build-up of BTs in
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roadside snow-piles and preferential partitioning of BTs to the liquid phase of a melting
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snowpack leads to early peaks in [ΣBTs] in both streams, except the sites in the Little Rouge
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Creek with low levels of vehicle traffic. Overall, a history of BT release and land use associated
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with urbanization have led to higher levels of BTs in urban areas, and provide a glimpse into
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future BT dynamics in mixed use, (sub)urbanizing areas.
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Environmental Science & Technology
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INTRODUCTION
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Benzotriazoles (BTs) are a group of emerging contaminants with a myriad of commercial uses
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due to their effectiveness in inhibiting metal corrosion. The most commonly used anti-corrosive
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BTs include 1H-benzotriazole (1H-BT) and 4- and 5-methylbenzotriazole (4- and 5-MeBT). The
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ubiquity of metal usage across society means that BTs are used as additives or intermediates in
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the production of a range of goods including aircraft de-icing and anti-icing fluids (ADAF),
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vehicle antifreeze, dishwashing detergent and dyes.1
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1H-BT and 4- and 5-MeBT are relatively water soluble (19.8 and 5.5 g/L at 25°C for BT and
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MeBTs respectively) and involatile compounds.2 Recent reviews33333,4 indicate that these
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compounds, particularly 1H-BT and 4-MeBT, are largely resistant to degradation under
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environmental conditions, and exert low acute toxicity to lower trophic level aquatic organisms.
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Levels in environmental waters near high-traffic airports may exceed toxicity thresholds,5,6 due
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to a combination of high emissions from ADAF use and persistence. Chronic toxic effects and
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general toxicity to higher trophic level organisms remain poorly characterized.3,4 Nevertheless,
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1H-BT has been labelled a suspected human carcinogen.1 To date, Australia is the only country
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to introduce drinking water guidelines for BTs, with a recommended threshold level of 7 ng/L
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for 5-MeBT.7 BT residues have recently been detected in human urine from populations in Asia,
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North America and Europe8, and in human adipose tissues in the United States9, suggesting the
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potential for bioaccumulation of these compounds.
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As a result of their poor degradability and wide usage, BTs are ubiquitous in surface waters and
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wastewater treatment plant (WWTP) effluents around the world.10-15 While these studies have
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been able to establish the widespread presence of BTs and links to sources such as WWTPs and
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airports, a mechanistic knowledge of BT delivery from source to streams is lacking. Major
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sources of BTs are clearly associated with activities in urban areas, but the ways in which the
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urban water cycle influences the transport of BTs to stream channels is unclear.
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Stable water isotopes have long been used as tracers in hydrograph separations to help illuminate
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water transport pathways in relatively undisturbed landscapes. These studies have revealed that
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the majority of streamflow during high runoff events is mostly “pre-event”, i.e. watershed
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storage, dominated by groundwater flows, rather than “event” water, i.e. fresh rain or snow
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inputs and directly associated surface runoff.16 This technique has been sparingly applied to
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storms and snowmelt in urban areas. More intense urbanization seems to lead to greater event
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water contributions to streamflow during snowmelt and storms that range from 24% in
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watersheds with relatively low proportions of urbanized land,17,18 to 48-58% in a suburban
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watershed with 60% urban land use,19 18-78% in a 72% residential watershed,20 and 78% in one
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of the most densely suburbanized watersheds in Canada.21 In a mixed-cover catchment in
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Pennsylvania, event water contributions at peak flow increased from primarily agricultural (
