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Perchlorate in lake water from an operating diamond mine Lianna J.D. Smith, Carol J. Ptacek, David W. Blowes, Laura G. Groza, and Michael C. Moncur Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 03 Jun 2015 Downloaded from http://pubs.acs.org on June 4, 2015
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Environmental Science & Technology
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Perchlorate in lake water from an operating diamond
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mine
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Lianna J.D. Smith*†‡, Carol J. Ptacek†, David W. Blowes†, Laura G. Groza†, Michael C.
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Moncur†§
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Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON,
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Canada N2L 3G1
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Lianna Smith Consulting, Ottawa, ON, Canada K1S 4Y5
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Alberta Innovates – Technology Futures, Calgary, Alberta, Canada T2L 2A6
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Corresponding Author
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*Corresponding author email:
[email protected] 11
Present Addresses
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†
University of Waterloo
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‡
Lianna Smith Consulting
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§
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Abstract
Alberta Innovates – Technology Futures
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Mining-related perchlorate [ClO4-] in the receiving environment was investigated at the
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operating open pit and underground Diavik diamond mine, Northwest Territories, Canada.
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Samples were collected over four years and ClO4- was measured in various mine waters, the 560
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km2 ultra-oligotrophic receiving lake, background lake water and snow distal from the mine.
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Groundwaters from the underground mine had variable ClO4- concentrations, up to 157 µg L-1,
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and were typically an order of magnitude higher than concentrations in combined mine waters
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prior to treatment and discharge to the lake. Snow core samples had a mean ClO4- concentration
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of 0.021 µg L-1 (n=16). Snow and lake water Cl-/ClO4- ratios suggest evapoconcentration was not
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an important process affecting lake ClO4- concentrations. The multi-year mean ClO4-
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concentrations in the lake were 0.30 µg L-1 (n=114) in open water and 0.24 µg L-1 (n=107) under
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ice, much below the Canadian drinking water guideline of 6 µg L-1.
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concentrations of ClO4- generally decreased year-over-year and ClO4- was not likely
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[biogeo]chemically attenuated within the receiving lake. The discharge of treated mine water
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was shown to contribute mining-related ClO4- to the lake and the low concentrations after 12
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years of mining were attributed to the large volume of the receiving lake.
Receiving lake
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Introduction
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Perchlorate [ClO4-] salts are used as an oxidant for propellants including solid rocket fuel,
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munitions, igniters, pyrotechnic devices, and explosives (1, 2), as well as additives in various
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manufacturing processes (2, 3). The physical and chemical nature of ClO4- makes it highly
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soluble, extremely mobile and stable in oxic groundwater and surface water with little tendency
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to adsorb to mineral or organic surfaces, thus, the ClO4- anion is conservative in many settings
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(4). Microbial reduction of ClO4- has been shown to occur in amended and unamended anoxic to
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suboxic soils, groundwaters and treatment systems by facultative anaerobic (or microaerophillic)
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dissimilatory perchlorate reducing bacteria (5, 6, 7). One study identified isolates of aerobic
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perchlorate reducing bacteria in soils (8).
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Perchlorate is a contaminant of concern in water because it is a thyroid endocrine disruptor,
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inhibiting iodine uptake (9) and impacting neurodevelopment in fetuses and infants (e.g. 10). In
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response to human health concerns, the USEPA issued an interim health advisory of 15 µg L-1
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ClO4- while the regulation was being developed (11). The Canadian drinking water guideline for
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ClO4- is 6 µg L-1 (12). Ecotoxicity effects of ClO4- can include abnormal development and
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growth in aquatic organisms, and 9.3 mg L-1 was calculated for a ClO4- continuous concentration
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criterion for aquatic life (13).
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Treatment technologies such as reverse osmosis, (electro)chemical reduction and adsorption
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technologies have been shown to be effective, but with various challenges that limit wide-spread
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application. Biological reduction and ion exchange technologies are more typically applied (14,
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15, 16).
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Perchlorate has been reported in groundwater and/or surface water in Antarctica (17), Canada
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(18), China (19), Germany (20), India (21), Israel (22), Japan (23), Korea (24) and the United
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States (e.g. 25 –28). Sources of ClO4- include naturally-occurring ClO4-, and anthropogenic
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residues. Suspected or confirmed surface and groundwaters impacted by naturally-occurring,
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atmospherically-derived deposits have been identified in Antarctica (29, 17), the Atacama desert
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(30), and the southwestern United States (25, 26, 31, 32). Anthropogenic groundwater and
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surface water ClO4- contamination has been associated with munitions and explosives
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manufacturing, and current and former military facilities (e.g. 2). Surface water contamination
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has been reported from fireworks displays (33). Dry and/or wet deposition of ClO4- has been
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documented in the United States (31, 34) and in ice cores from the Canadian high Arctic (35).
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Several studies have identified mining-impacted lakes and rivers (e.g. 36 and references therein),
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and one study (37) has documented concentrations of residuals from blasted mine waste rock,
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including concentrations of ClO4-, from drainage collected from large-scale, experimental waste-
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rock piles (38) and laboratory experiments. However, no published studies have focused on
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ClO4- in the receiving environment related to mining activities.
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Open pit and underground mining uses explosives to fragment ore and waste rock during
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mining. The explosives used in mining include ammonium nitrate prill (AN; [NH4NO3]) mixed
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with fuel oil (ANFO) and/or emulsion, detonated with a boosting agent containing ClO4- salts
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(e.g. KClO4). Detonator boosting agents can contain 4 to 60 mg ClO4- per detonator (39). A
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small percentage of explosives remain undetonated after a blast. These residual nitrogen species
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[N-species] and ClO4- dissociated from KClO4 can be used as resident tracers for blasting-
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impacted mine drainage (37). The AN in the bulk explosive is highly hygroscopic and water
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soluble. ANFO is typically 94% AN and 6% fuel oil, containing 33 wt.% N and typical
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emulsions contain 20 to 30 wt.% N (40). In water, NH4NO3 dissociates to nitrate [NO3-] and
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ammonium [NH4+]. Nitrification of NH4+ under aerobic conditions by nitrifying bacteria can also
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produce the intermediate N species nitrite [NO2-], which can be further oxidized
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microbiologically to NO3- (41). Like ClO4-, NO3- is a persistent anion in oxic groundwater and
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surface water systems with little capacity to adsorb (42), but may be bacterially reduced. From a
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thyroid health perspective, NO3- may interact additively with ClO4- to inhibit iodine uptake (43,
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44).
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This study presents data from the Diavik Diamond Mine (Diavik), an operating diamond mine
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located on an island in an ultra-oligotrophic lake in the Northwest Territories, Canada (Figure 1).
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Concentrations of ClO4-, Cl- and N-species were measured in mine waters, the surrounding lake,
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a background lake, and distal snow. The objectives of this study were to determine if mining
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operations produced measureable ClO4- in various mine waters and if mining effluent contributed
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ClO4- at concentrations sufficient to impact a receiving lake.
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Experimental Section
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Site description
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Diavik is an operating diamond mine in a continuous permafrost region of the Canadian Shield
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in the Northwest Territories, Canada. Development and mining occurred in open-pits from
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2002-2012 and underground from 2006, and is on-going. Air temperatures range from a mean
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temperature of 18 ºC in July to a temperature of -31 ºC in January and February, with an annual
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mean of -9.3 ºC. Approximately 40% of the 280 mm annual mean precipitation (1999-2008)
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occurs as snow (45).
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Figure 1. Location of the Diavik Diamond Mine (Diavik), Northwest Territories, Canada. After
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(34).
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The mine infrastructure is located on a 20 km2 island within the ultra-oligotrophic lake Lac de
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Gras, which also serves as the drinking water source for the mining operation. Lac de Gras is
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560 km2 with a mean depth of 12 m, a maximum depth of 56 m, and an estimated volume of 6.7
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billion m3. The mean annual inflow and outflow are 19 m3 s-1 and 21 m3 s-1, respectively with a
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residence time of 11.3 a. Lac de Gras has a drainage area of 3,560 km2 and forms the headwaters
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of the Coppermine River, which flows to the Arctic Ocean near the community of Kugluktuk.
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The mean annual ice cover for Lac de Gras is 250 days per year, typically October to July with
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ice thicknesses up to 1.7 m. The estimated mean evaporation during open water season is 236
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mm and the lake does not stratify thermally in either open water or ice covered seasons. Lac de
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Gras is oxic with low concentrations of nutrients and dissolved constituents (Supporting
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Information). Lac du Sauvage is an ultra-oligotrophic lake upstream of Lac de Gras with current
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concentrations of the major ions similar to pre-mining concentrations in Lac de Gras, and current
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concentrations of the major ions significantly lower (P
