W. Lyle Lockhart

Spatial trends and historical profiles of organochlorine pesticides in Arctic lake sediments

Sediment cores were collected from eight remote lakes in Canada, along a mid-continental transect from 49°N to 82°N, with the objective of examining latitudinal and temporal differences in deposition of a wide range of persistent, semi-volatile, organochlorine (OC) pesticides such as DDT, dieldrin, hexachlorobenzene (HCB), hexachlorocyclohexane (HCH), and toxaphene. Samples were collected with a specially constructed ☐ corer (30 × 30 cm), or with large (10-cm) KB corers, from the deep basins of lakes at the Experimental Lakes Area (ELA) (49°30′N), Saqvacjuaq (63°39′N), Cornwallis Island (75°07′N), Axel Heiberg Island (79°N), and Northern Ellesmere Island (Lake Hazen; 82°N). Sediment slices were dated using210Pb and137Cs. Sediment extracts were analyzed by high-resolution GC-ECD with confirmation by GC-MS. Concentrations of total DDT ( ΣDDT) in surface sediments (0–1.3 cm depth) declined significantly with latitude from 9.7 ng/g (dry wt.) in ELA sediments to 0.10 ng/g in Lake Hazen. HCB levels showed a reverse trend; organic carbon normalized concentrations increased with latitude. Concentrations of other OC pesticides (total HCH, total chlordane, toxaphene, and dieldrin) were generally in the range of 0.1–3 ng/g, with the sites at 63°N and 75°N generally having the highest levels. The profiles of ΣDDT and total chlorobenzenes in all the mid-continental lakes showed maxima in slices dated from the late 1970s to the 1980s, which is about 5–10 years later than maxima reported for Lake Ontario. The results generally support several of the predictions of the cold condensation hypothesis.

Mercury Concentrations in the Food Web of Lake Malawi, East Africa

Little is known about the concentrations of mercury (Hg) and factors affecting this contaminant in tropical freshwater biota. Lake Malawi, an East African Rift Valley lake, is internationally renowned for having the highest diversity of fish species in the world, and the lake supports subsistence fisheries for the three riparian countries. In this study the concentrations of Hg in fish and invertebrates collected from the lake in 1996 and 1997 were examined, and tissue stable carbon (δ13C) and nitrogen (δ15N) isotopes were used to distinguish and contrast those consumers relying upon carbon fixed by either benthic or pelagic primary producers, and their trophic positioning. Concentrations of Hg were generally low (2 to 200 ng/g wet weight) in fish from Lake Malawi. In addition, pelagic fish contained significantly higher concentrations of Hg than the benthic species. As in temperate systems, log-transformed Hg concentrations were significantly predicted by δ15N and the highest concentrations of Hg were found in the largest fish within each species. The rate of Hg accumulation was not significantly different between the pelagic and benthic fishes but pelagic species had significantly higher Hg concentrations at a common weight and trophic position. The slope of the Hg-δ15N relationship in Lake Malawi was comparable to what has been found in temperate and arctic lakes, suggesting that Hg accumulation in freshwater food webs is independent of climatic factors and species composition.

Historical contamination of Yukon Lake sediments by PCBs and organochlorine pesticides: influence of local sources and watershed characteristics.

PCBs and other persistent organochlorine (OC) pesticides were analyzed in sediment cores collected from six lakes in Yukon Territory and one in northern British Columbia, Canada, with the objective of establishing sources and historical trends of these contaminants. DDT was found to be the most prominent OC in the sediment profiles of most of the lakes. Maximum sigmaDDT levels (3.47-2680 ng g(-1) dw) were observed in sediment slices dated to the 1950s from lakes near populated areas. In contrast, in more remote lakes (Hanson, Kusawa and Lindeman), the maximum sigmaDDT concentrations were observed in the sediments dated to the 1970s. Highest sigmaPCB and sigmaDDT concentrations were measured in sediments from Watson Lake, near a suspected PCB waste disposal site and in a region where DDT was heavily applied in the 1950s and 1960s. Elevated sigmaPCB concentrations [16.1-93.6 ng g(-1) dry weight (dw)] were also observed in sediments from lakes situated near populated areas, relative to Kusawa and Lindeman (11.1 and 12.7 ng g(-1) dw, respectively). Recent sigmaPCB fluxes ranged from 621 ng m(-2) y(-1) in Kusawa Lake to 16400 ng m(-2) y(-1) in Little Atlin Lake. The extremely high sedimentation rate (2050 g m(-2) y(-1)) in glacial fed Lindeman Lake gave rise to elevated fluxes of sigmaPCB (2410 ng m(-2) y(-1)) and other OCs, despite much lower concentrations in the sediment. Levels of hexachlorocyclohexanes (sigmaHCH), chlordane-related compounds (sigmaCHL), and chlorobenzenes (sigmaCBz) were in the low ng g(-1) (dw) range in all lake sediments, similar to concentrations previously reported for Arctic lakes in Canada, indicating that their major source was long range atmospheric transport. Contamination of the lakes with PCBs and DDT near populated areas of the Yukon Territory appears to be a result of regional activities rather than long range transport and deposition. The results also point to glacial runoff as a significant source of OCs to small, high elevation lakes (Lindeman), but not to larger lakes within the Yukon River drainage basin that are also affected by glacial sources (Kusawa, Laberge).

Dietary 2,3,7,8-tetrachlorodibenzofuran in rainbow trout: Accumulation, disposition, and hepatic mixed-function oxidase enzyme induction☆

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to dietary 2,3,7,8-[3H]tetrachlorodibenzofuran (TCDF) (0.36 to 42.8 ng g-1) and accumulation, tissue distribution, biotransformation, and hepatic monooxygenase enzyme (MO) induction were studied. The assimilation efficiency of TCDF ranged from 49 to 62% in 30-day exposures and was independent of the TCDF level in the diet. Depuration half-lives (whole body) of TCDF following 30-day exposure ranged from 40 to 77 days and were significantly more rapid in fish exposed to 42.8 ng g-1. Liver somatic index (LSI) and rate of increase in liver weight were elevated in fish exposed to 42.8 ng g-1 TCDF compared to controls. Exposure to 9.2 ng g-1 TCDF in the diet for 140 days also resulted in higher LSI values, as well as increased mortality (16%), but had no significant effects on growth. [3H]TCDF was found mainly in the carcass (63-74%) and GI tract (18-31%), with lesser amounts in liver (0.6-2.3%) during the 140-day exposure, primarily (> 98%) in the form of the parent compound. Radioactivity in bile was found mainly as a single polar transformation product by reverse-phase HPLC. Glucuronidase hydrolysis yielded a product with the retention time expected of hydroxylated TCDF, suggesting the presence of a glucuronide conjugate. MO enzyme induction measured by ethoxyresorufin-O-deethylase (EROD) activity in liver (postmitochondrial supernatant) was 137.5 and 15 times higher than that in control fish after 30 days dietary exposure to 42.8 and 9.2 ng g-1, respectively. EROD activities were correlated with TCDF concentrations in liver (R2 = 0.59, N = 45).

Implications of chemical contaminants for aquatic animals in the Canadian arctic: some review comments.

Chemical residue analyses have established beyond doubt that arctic ecosystems are contaminated with low concentrations of several contaminants. The sources of these vary, but for many, the principal source is atmospheric deposition as a result of widespread dispersal by air masses carrying materials from lower latitudes. The principal problem discussed here is how to determine whether there are biological implications associated with the contaminants. For the most part, concentrations are below those found in more temperate regions where similar questions have been asked. Little experimental toxicology has been done with arctic species, and relatively little has been done in environmental toxicology in general to express biological responses in terms of body residues. It is argued that chemical residue studies are not, in themselves, evidence of biological responses. The effects of greatest interest are those at ecological levels, but ecological surveys that might detect biological changes have little power to test for cause-effect linkages between the contaminants and the changes observed. The emerging approach of biomarkers or bioindicators seems to offer the greatest promise for efforts to determine whether arctic contaminants have biological implications.

Accumulation, depuration and hepatic mixed-function oxidase enzyme induction in juvenile rainbow trout and lake whitefish exposed to dietary 2,3,7,8-tetrachlorodibenzo -p-dioxin

Abstract Juvenile rainbow trout (Oncorhynchus mykiss) and lake whitefish (Coregonus clupeaformis) were exposed to three concentrations (40, 190, 400 pg g−1) of dietary 2,3,7,8-[ 3 H ] tetrachlorodibenzo-p-dioxin (TCDD) to compare bioaccumulation and hepatic monooxygenase enzyme (MO) induction. Fish were exposed for 30 days followed by a 180 day depuration phase. Differences in the accumulation and depuration of TCDD were found between rainbow trout and lake whitefish, despite similar body size and lipid content. Assimilation efficiencies of TCDD were greater in lake whitefish (66–76%) than rainbow trout (43–58%), but TCDD half lives were shorter in lake whitefish (32–39 days) than in rainbow trout (73–83 days). Biomagnification factors (BMF) ranged from 1.6 to 1.8 in rainbow trout and from 0.8 to 0.9 in lake whitefish, confirming the known potential for biomagnification of TCDD in aquatic food webs. Reverse phase HPLC showed that a majority of the radioactivity in the rainbow trout bile was TCDD, with minor amounts present as a hydroxylated TCDD and as a glucuronide conjugate. MO enzyme induction, measured by ethoxyresorufin-O-deethylase (EROD), was observed in the rainbow trout after 10 days of exposure to 400 pg g−1 TCDD, and in the lake whitefish after 5 days of exposure to 380 pg g−1 TCDD. The whole fish threshold concentration for EROD induction by TCDD ranged between 15 and 45 pg g−1 (wet weight) for both species. EROD activity returned to control levels 120 and 80 days after the cessation of the treatments in the rainbow trout and lake whitefish, respectively. Growth rates were significantly reduced in trout and whitefish at whole fish concentrations (wet weight) of 150 ± 4.6 and 85 ± 8.3 pg g−1, respectively. Histological effects of the TCDD were found in the spleen and liver of the rainbow trout which had whole fish concentrations (wet weight) of 150 ± 4.6 pg mg−1and 72 ± 8.0 pg mg−1 TCDD, respectively.

Bioassays with a floating aquatic plant (Lemna minor) for effects of sprayed and dissolved glyphosate

Macrophytes in forested areas and in prairie wetlands furnish critical habitat for aquatic communities and for several species of birds and mammals. North American agriculture relies heavily on herbicides and these compounds are detected routinely in surface waters of Western Canada. The question is whether these residues have biological meaning. There is surprisingly little literature on the responses of macrophytes to herbicides, or indeed to other chemicals. Previously we have used common duckweed in efforts to detect effects of herbicides and other chemicals. Duckweed clones were developed from local collections and grown axenically. In this study the plants were exposed to glyphosate herbicide either by dissolving formulated Roundup® (Monsanto Canada Inc.) in the culture media or by spraying of the cultures in a laboratory spray chamber. Plant growth was monitored by counting the fronds present on several occasions over a 2-week period following treatment and by taking wet and dry weights of plants after the final counting period. Plant growth, as measured by increased numbers of fronds or increased wet or dry weights was relatively insensitive to glyphosate dissolved in the culture medium. However, the plants were killed by application of glyphosate as a spray.

Assessing Trends in Organochlorine Concentrations in Lake Winnipeg Fish Following the 1997 Red River Flood

Abstract As we move toward the virtual elimination of persistent organic pollutants (POPs) in the environment our understanding of how short-term variability affects long-term trends of POPs in natural populations will become increasingly more important. In this study we report short-term trends in organochlorine (OC) levels in fish from Lake Winnipeg in the months and years following the 1997 100-year flood of the Red River ecosystem. Our goal was to understand the effects of an episodic event on OC levels in benthic and pelagic invertebrates and in fish. Despite elevated loading of OCs into the south basin of Lake Winnipeg during the flood there were no differences in OC levels of surface sediments or emergent mayflies. After adjusting for differences in lipid content and length among sample times, we did find significant increases in total DDT (ΣDDT) and total polychlorinated biphenyl (ΣPCB) post-flood (March 1999) in top predators including walleye and burbot. Significant increases were also observed in OC concentrations of zooplankton and yellow perch (> 2 fold in ΣPCB, ΣDDT, total chlordane (ΣCHL), total chlorobenzenes (ΣCBZ)) and walleye (1.4 fold ΣPCB) over a 2-month period in the summer following the flood. Analysis of specific congener patterns over time suggest that the major changes in fish OC levels pre- and post-flood did not appear to be linked to transport of new compounds into the Lake during the flood, but to species shifts within the plankton community. Our results indicate that short-term variation (∼2 months) in OC distributions within biota may be equal to or greater than those resulting from episodic events such as spring floods.

Baseline studies in the Slave River, NWT, 1990–1994: Part III. MFO enzyme activity in fish

Abstract As part of the Slave River Environmental Quality Monitoring Program, a background data set of baseline concentrations was collected for various environmental components including fish, water, bottom sediment, and suspended sediment. Fish collections included a serics of hepatic MFO analyses on walleye, northern pike, lake whitefish, and burbot. The EROD and AHH activity and P450 levels of fish, as well as weight, length, age, condition factor, and liver and gonadal somatic indices are described. Levels of EROD and AHH activity were of an order of magnitude expressed by the following relationship: walleye > northern pike > burbut > lake whitefish. Males consistently showed higher EROD, AHH activity and cytochrome P450 content relative to females of the same species even at control sites. Physical parameters varied very little within sites and exhibited some differences with the reference sites. A good MFO data set was collected for walleye and northern pike, but limited conclusions were possible with the lake whitefish and burbot data due to the overlap of sampling with the spawning season. Hepatic MFO enzyme activity indicated that some differences were evident in fish sampled from the Slave River relative to background/reference lakes; however, in many cases no differences were observed. Five years of biochemical effects studies have determined that the Slave River had low levels of induction suggesting a relatively pristine environment. This is further supported by the water, sediment, and body burden chemistry components of the Slave River Environmental Quality Monitoring Program.

Historical Deposition of PCBs and Organochlorine Pesticides to Lake Winnipeg (Canada)

Two dated sediment cores; one taken from the north basin and one from the south basin of Lake Winnipeg (Manitoba, Canada) were analyzed for PCBs and organochlorine insecticides in order to examine the depositional history of these persistent organic pollutants (POPs). No previous work had been conducted on current or historical deposition of POPs in Lake Winnipeg sediments. Analysis by high resolution gas chromatography—electron capture detection showed elevated PCB concentrations in sediments dated to the late 1960s to early 1970s. Recent PCB fluxes were estimated to be 5 to 11 μg/m2/y in Lake Winnipeg sediments, with burdens of 388 and 337 μg/m2 in the north and south basins, respectively. Loadings in the north basin sediment indicated atmospheric sources; south basin sediment reflected inputs from agricultural, industrial, and urban activities. DDT inventories were 37 and 127 μg/m2 in the north and south basin cores, respectively. DDD contributed the largest amount to DDT in sediments, corresponding to anaerobic degradation of the parent molecule. Maximum hexachlorocyclohexane (HCH) concentrations were observed in recent slices of both sediment cores and fluxes ranged from 177 to 914 ng/m2/y. There was evidence for recent increases in lindane deposition. Subsurface maximum concentrations were observed for total chlordane (ΣCHL), pentachloroanisole (PCA), and total chlorobenzenes (ΣCBz) in the south basin. ΣCHL, PCA, and ΣCBz, however, were present at maximum concentrations in the surface slice in sediment from the north basin.