Environ. Sci. Technol. 1999, 33, 1794-1798
Delayed Deposition of Organochlorine Pesticides at a Temperate Glacier DAVID B. DONALD,* JIM SYRGIANNIS, AND ROBERT W. CROSLEY Environment Canada, Room 300 Park Plaza, 2365 Albert Street, Regina, Saskatchewan, Canada S4P 4K1 GERALD HOLDSWORTH Arctic Institute of North America, University of Calgary, Calgary, Alberta, Canada T2N 1N4 DEREK C. G. MUIR Environment Canada, National Water Research Institute, Burlington, Ontario, Canada L7R 4A6 BRUNO ROSENBERG Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba, Canada R3T 2N6 ALBI SOLE Yamnuska Mountain School, 1360 Railway Avenue, Canmore, Alberta, Canada T0L 0M0 DAVID W. SCHINDLER Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
Many of the organochlorine pesticides that were once widely used have either been banned or uses have been restricted in Canada and the United States. Near areas of high pesticide use at mid-latitudes in eastern North America, environmental levels of some of these pesticides peaked in the 1960s, and all have declined at least since the late 1970s. We determined depositional trends in a midlatitude temperate glacier in Alberta, western Canada (52° N, 117° W). In contrast to trends in eastern North America, ∑DDT, dieldrin, and ∑chlordane reached peak concentrations (2.57, 0.05, and 0.07 ng/L, respectively) and maximum flux to this cold high elevation environment in the 1980s at least 1 decade after they had been banned and maximum use had occurred in North America. From 1959 to 1995, a significant decline was evident for R-HCH (r 2 ) - 0.64, p < 0.001). A significant severalfold increase and positive trend (r 2 ) 0.17, p < 0.03) was evident for hexachlorobenzene with maximum flux occurring in the 1990s. Lindane and ∑chlordane had a distinct bimodal depositional pattern with peak concentrations occurring about 1960 and again in 1989. Meltwater from glaciers may contribute high concentrations of pesticides to cold aquatic ecosystems for decades or centuries.
Introduction Organochlorine pesticides have been widely used since their introduction in the 1940s and 1950s. By the early 1970s, their * Corresponding author telephone: (306)780-6723; fax: (306)7805311; e-mail:
[email protected]. 1794
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fate within ecosystems and negative effects on species were generally known. These included bioaccumulation and biomagnification within food webs, persistence, and volatilization and transport in the atmosphere (1-7). As a result, restrictions on their use in Canada and the United States began in the 1970s (Table 1). By the 1990s in these countries, most of the organochlorine pesticides were either severely restricted, banned, or their production was voluntarily discontinued. Although uses of organochlorine pesticides have been restricted in some other countries (8, 9), they continue to be used to control human and agricultural pests, particularly in Third World countries. Records of use of pesticides in many of these countries are difficult to obtain because the information is confidential, is not collected, or is not reported to the United Nations Food and Agricultural Organization (10). Although use of organochlorine, or more precisely the cyclodiene, pesticides has declined in North America, there is growing concern that their residues continue to have adverse sublethal effects on species and ecosystems. These include the disruption of reproductive systems of wildlife (11) and the development of cancer in humans (12, 13). Moreover, some arctic and subarctic wildlife are contaminated by high levels of organochlorine contaminants of atmospheric origin, and there is concern for aboriginal consumers of country foods (14, 15). We measured the long-term depositional history of organochlorine pesticides within a mid-latitude Canadian glacier at Snow Dome Mountain. Long-term deposition trends for organochlorine pesticides have been determined from lake and reservoir sediment (2, 16, 17), from peat cores (1, 18), and in ice from an arctic glacier (19). We hypothesized that declining uses of these chemicals in North America and elsewhere (Table 1) would result in declining deposition and concentrations at Snow Dome from the 1970s to 1995, the year of our study. Snow Dome is within a pristine region of the national parks in the Rocky Mountains where agriculture and consequently pesticide use is inconsequential. Air masses at Snow Dome (5-day back-trajectories) originate from continental Canada and the United States about 32% of the time during the year and from the Pacific Ocean and Asia about 68% of the time (20). However, the frequency of air mass origin from continental North America increases to 54% of the time from May to July when precipitation and concentrations of pesticides in the air are highest (21). During these months, high summer temperatures could remobilize volatile pesticide residues to the atmosphere from much of southern North America (22). Thus, the potential sources for the pesticides deposited at Snow Dome are Canada, United States, Asia, and probably Mexico. Snow Dome is at the apex of the Continental Divide within the Front Range of the Rocky Mountains of southern Canada (52°11′ N, 117°19′ W). The summit is at 3506 m above sea level and, with other nearby mountains, forms the Columbia Icefields. Meltwater from Snow Dome flows to the Arctic Ocean by the Athabasca and then the Mackenzie rivers, to the Pacific Ocean by the Columbia River, and to the Atlantic Ocean by the Saskatchewan-Nelson River system. Snow falls year-round near the summit. The annual rate of snow accumulation varies from one site to another by 1-3 m because of redistribution by prolonged and severe wind.
Materials and Methods We used a new approach to collect snow and ice which, compared to ice cores, avoided the high cost of obtaining samples and at the same time provided the large volumes 10.1021/es981120y CCC: $18.00
1999 American Chemical Society Published on Web 04/24/1999
TABLE 1. Commerical Introduction and Status for Organochlorine Insecticides in Northern North Americaa status to 1998 pesticide DDT
introduced
Canada
United States
severely restricted in early 1970s, banned in 1973 few remaining products banned in 1985 dieldrin 1949 severely restricted in 1978, agricultural uses banned in 1975 remaining products discontinued in 1989 heptachlor 1952 discontined in 1985 most uses suspended in 1975, seed treatment banned in 1989 chlordane late 1940s, most uses suspended in 1986, most uses suspended in 1975, standardized 1950 discontinued in 1990 banned in 1988 lindane 1942 seed treatment for canola, restricted domestic, agriculture, limited domestic use and industrial use R-HCH 1940s no significant historical use no use after the 1950s endosulfan 1956 limited agricultural use used on a wide variety of crops hexachlorobenzene 1945 agricultural and industrial chemical agricultural and industrial chemical a
1942
Sources: refs 32, 37, 41, Agriculture Canada, and U.S. Environmental Protection Agency.
of water required for trace organochlorine analyses. In 1995, members of our team collected samples from Snow Dome Glacier by entering a crevasse at 3100 m elevation and climbing down a nearby ice-cliff at 3300 m elevation. Experienced alpine guides and modern ice-climbing techniques and safety equipment were used. Snow or ice samples were taken from each annual stratum from 1984 to 1995 and every other year from 1959 to 1984. Samples were taken from near the top and bottom for each of the 1984-1995 strata with the mean concentration of the two samples used for trend analyses. Annual strata in temperate glaciers are recognized by alternating couplet bands of opaque and clear ice (23). The latter band forms in late spring and summer and in the following year tends to seal the annual snowpack from inter-stratum percolation of the limited summer meltwater. An ice core retrieved from the summit of Snow Dome in 1984 by Holdsworth contained a verified forest fire ash layer in the summer clear ice layer at a depth of 11.3 m. Using stratigraphic, isotopic, and chemical data, the layer date was estimated to be close to 1970. Examination of the forest fire history of British Columbia and interviews with ski mountaineers in the region at that time revealed that the layer corresponded to early August 1971. In 1995, this same ash layer was discovered in the ice cliff at the 1971 stratum. Below the 1969 stratum, stratigraphy was less distinct and counting annual layers was more subjective. To help overcome this problem, a depth-time curve was extended to 1959 using a mean layer thickness corrected for thinning due to increasing density of the ice. To determine annual inputs of pesticides (per square meter) to Snow Dome, we assumed a uniform 1 m annual snowpack and a 3/10 ratio for water to snow. We then multiplied concentration per liter by the annual water equivalent of the snowpack (300 L) to obtain approximate deposition. Clean-room techniques were used to collect the snow and ice samples. Technicians wore a new outer layer of MicroClean Tyvek coveralls, hat, and gloves each day. Sampling equipment, including a stainless steel hammer, chisel, and snow/ice containers, was washed and rinsed with organicfree water; rinsed with pesticide grade acetone, and then hexane; and transported to the field in high molecular weight, high-density polyethylene bags. Snow and ice samples were melted in the laboratory in their closed field containers (=20 L water equivalent). To minimize re-equilibrium of the pesticides with the atmosphere, the samples were extracted as soon as the last bit of ice or snow melted with pesticide grade dichloromethane (DCM) in a Goulden liquid-liquid extractor (24, 25). The DCM extracts were shipped to the analytical laboratory (Freshwater Institute, Winnipeg) for analysis. The DCM extracts were dried over sodium sulfate (purified by heating 16 h at 600 °C), evaporated under
vacuum, and exchanged into hexane. The hexane extract was chromatographed on 1.2% deactivated Florisil (8 g), and three fractions (hexane, hexane:DCM (80:20), and hexane: DCM (1:1) were obtained as described in other studies (16, 26). Florisil elutes were analyzed by capillary gas chromatography (GC) with 63Ni electron capture detection (carrier gas hydrogen) on a 60 m × 0.25 mm DB-5 column using Varian 3400 or 3600 GC/data system (Varian Instruments, Palo Alto, CA) as described in other studies (21, 26). Concentrations of a total of 30 chlorinated chemicals were determined. Major peaks were confirmed in selected samples by GC-MS(HP 5971 MSD) using a 30 m DB-5 column with helium carrier gas. Analytes were quantified using an external standard method as described in Muir et al. (27). Recoveries of the surrogates and analytical results are presented in the Supporting Information (see paragraph at end of the paper). Method detection limit was determined as the instrument detection limit plus 3 × SD of the signal of the lowest concentration standard of each analyte, which was about 2 pg/L for all individual pesticides or isomers (28, 29). Analytical (instrument) variation is typically
