Michael Kwan - Academia.edu (original) (raw)

Papers by Michael Kwan

Science of The Total Environment, 2015

Temporal trends in perfluoroalkyl compounds (PFCs) were investigated in liver samples from two ri... more Temporal trends in perfluoroalkyl compounds (PFCs) were investigated in liver samples from two ringed seal (Phoca hispida) populations in the

Environmental Toxicology and Chemistry, 2014

Science of The Total Environment, 2005

Mercury (Hg) and cadmium (Cd) concentrations in ringed seal liver and kidney were compared from 1... more Mercury (Hg) and cadmium (Cd) concentrations in ringed seal liver and kidney were compared from 11 locations across the Arctic, from Alaska, Canada, Greenland, Svalbard to the White Sea. Adult and sub adult seals were evaluated separately to account for age accumulations of Hg and Cd. Only recently (1995-2001) collected samples were included to minimize influence of changes over time. The Hg and Cd concentrations in ringed seal liver and kidney differed significantly among the studied locations. The Hg concentrations in liver of ringed seals was highest in the western Canadian Arctic locations, while Cd in liver was highest in the eastern Canadian and West Greenland locations. In general, Hg and Cd concentrations in liver and kidney were significantly higher in adult ringed seals than in sub adults and the circumpolar patterns were most pronounced in adult ringed seals. The Hg and Cd concentrations in kidney of ringed seals in general supported the geographical pattern found in livers although the coverage was more limited. The most likely explanation for the observed circumpolar pattern appears mainly to be related to natural geological differences in mineral (Hg and Cd) among regions.

Journal of Toxicology and Environmental Health, Part A, 2006

have been reported in marine mammals on a global scale. While risk assessments are generally base... more have been reported in marine mammals on a global scale. While risk assessments are generally based on quantifying body burdens of toxicants, much less is known about associated adverse health effects and their underlying mechanisms. The purpose of this study was to characterize the inhibitory effects of methylmercury (MeHg + ), mercuric chloride (Hg 2+ ), p,p¢-DDT, Arochlor 1254, chlordane, dieldrin, lindane, and toxaphene on [ 3 H]quinuclidinyl benzilate ([ 3 H]-QNB) binding to the muscarinic cholinergic (mACh) receptor in cellular membranes isolated from the cerebrum of ringed seals (Phoca hispida). [ 3 H]-QNB binding to the mACh receptor was saturable with a mean receptor density (B max ) of 826.9 ± 68.4 fmol/mg and ligand affinity (K d ) of 0.31 ± 0.04 nM. MeHg + and Hg 2+ were the only neurotoxicants that inhibited radioligand binding by greater than 50%. Hg 2+ was significantly more potent at inhibiting mACh receptor binding than MeHg + when the IC 50 data were compared (IC 50 = 1.92 ± 0.06 mM versus 2.75 ± 0.22 mM), but when the data were normalized to derive inhibition constants (K i ) there was no statistical difference in inhibition (Hg 2+ = 1.38 ± 0.07 mM; MeHg + = 1.26 ± 0.12 mM ). Toxaphene also inhibited mACh receptor binding by 22.4%, but this was only significant at the highest concentration tested (320 mM). Overall, these data suggest that Hg, and not organochlorines, inhibits ligand binding to the mACh receptor. These mechanistic findings may be used to support and develop specific biomarkers of Hg exposure and neurotoxicity in sensitive ecological species.

Environmental Toxicology and Chemistry, 2007

The present study examined spatial trends of perfluoroalkyl compounds (PFCs) in liver samples fro... more The present study examined spatial trends of perfluoroalkyl compounds (PFCs) in liver samples from 11 populations of ringed seals (Phoca hispida) in the Canadian Arctic from 2002 to 2005. Trophic position and relative carbon sources were compared by analyzing stable nitrogen and carbon isotopes in muscle samples. Geometric mean concentrations of total C 9 -C 15 perfluorinated carboxylates (PFCAs) ranged from 8.8 to 84 ng/g wet weight, and C 9 -C 11 PFCAs predominated. Perfluorooctane sulfonate was the dominant PFC measured, with concentrations ranging from 6.5 to 89 ng/g wet weight, contributing between 29 and 56% of the total PFC concentration. Overall, mean PFC concentrations were similar between populations, and differences were attributed largely to elevated levels in the Gjoa Haven (Rae Strait, central Canadian Arctic archipelago) and Inukjuak populations (eastern Hudson Bay) and to lower concentrations at Pangnirtung (Cumberland Sound, Baffin Island). Mean stable nitrogen isotope ratios (Ϯ95% confidence intervals) ranged from 14.7‰ (Ϯ0.3‰) at Nain (Labrador) to 17.9‰ (Ϯ0.7‰) at Gjoa Haven, suggesting that all populations were within the same trophic level. Stable carbon isotope ratios varied widely between the seal populations, ranging from Ϫ22.9‰ (Ϯ0.2‰) at Gjoa Haven to Ϫ17.7‰ (Ϯ0.4‰) at Nain. The ␦ 13 C ratios from Gjoa Haven were significantly more depleted than those for other populations and may suggest a terrestrially based carbon source. The depleted stable carbon isotope ratio may explain the elevated PFC concentrations in the Gjoa Haven population. Analysis of covariance indicated that ␦ 13 C was a significant covariable for seven of nine seal populations for which ␦ 13 C values were available. After adjusting for ␦ 13 C values, concentrations of most PFCs generally were statistically greater in the Grise Fiord, Qikiqtarjuaq, Arviat, and Nain populations.

Environmental Science & Technology, 2007

Polybrominated diphenyl ethers (PBDEs) were determined in adipose tissue of adult and subadult fe... more Polybrominated diphenyl ethers (PBDEs) were determined in adipose tissue of adult and subadult female polar bears sampled between 1999 and 2002 from sub-populations in Arctic Canada, eastern Greenland, and Svalbard, and in males and females collected from 1994 to 2002 in northwestern Alaska. Only 4 congeners (BDE47, 99, 100, and 153) were consistently identified in all samples. BDE47 was the major PBDE congener representing from 65% to 82% of the sum (Σ) PBDEs. Age was not a significant covariate for individual PBDEs or ΣPBDE. Higher proportions of BDE 99, 100, and 153 were generally found in samples from the Canadian Arctic than from Svalbard or the Bering-Chukchi Sea area of Alaska. Geometric mean ΣPBDE concentrations were highest for female polar bear fat samples collected from Svalbard (50 ng/g lipid weight (lw)) and East Greenland (70 ng/g lw). Significantly lower ΣPBDE concentrations were found in fat of bears from Canada and Alaska (means ranging from 7.6 to 22 ng/g lw).

Environmental Research, 2012

Methylmercury (MeHg) is a neurotoxicant that has been found at elevated concentrations in the Arc... more Methylmercury (MeHg) is a neurotoxicant that has been found at elevated concentrations in the Arctic ecosystem. Little is known about its internal dose in wildlife such as polar bears. We measured concentrations of mercury (Hg) in three different brain regions (cerebellum, frontal lobe and brain stem) of 24 polar bears collected from the Nunavik, Canada between 2000 and 2003. Speciation of Hg was measured by High Performance Liquid Chromatography coupled to Inductively Coupled Plasma Mass Spectroscopy (HPLC-ICP-MS). Concentrations of mean total Hg in brain tissue were up to 625 times lower (0.28 7 0.07 mg kg À 1 dry weight (dw) in frontal lobe, 0.237 0.07 mg kg À 1 dw in cerebellum and 0.12 7 0.03 mg kg À 1 dw in brain stem) than the mean total Hg concentration previously reported in polar bear liver collected from Eastern Baffin Island. Methylmercury (MeHg) accounted for 100% of the Hg found in all three brain regions analyzed. These results suggest that polar bear might reduce the toxic effects of Hg by limiting the uptake into the brain and/or decrease the rate of demethylation so that Hg can be excreted from the brain more easily. The toxicokinetics and the blood-brain-barrier mechanisms of polar bears are still unknown and further research is required.

Environmental monitoring and assessment

In order to evaluate the use of zebra mussels as biomonitors for metal bioavailability in the St.... more In order to evaluate the use of zebra mussels as biomonitors for metal bioavailability in the St. Lawrence River, we tested the hypothesis that the concentrations of 11 metals in zebra mussels vary significantly between sites along the river and that the season of collection and body size affect metal bioaccumulation. Mussels were collected at 14 sites during June 1996 and at monthly intervals at one site. Specimens were grouped in three size classes and their soft tissue was analyzed for As, Ca, Cd, Cr, Hg, Mn, Ni, Pb, Se, and Zn. Significant size effects were found for Ca, Cd, Cr, Cu, Ni and Zn. Spatial and seasonal variations in bioconcentration were significant for all metals. Spatial patterns in contamination that corresponded to known point sources of pollution or hydrology of the river were identified by principal component analysis. Seasonal variations can be attributed to the reproductive cycle of mussels and hydrological variability of the river. In comparison with values ...

Science of The Total Environment, 2005

This review summarizes and synthesizes the significant amount of data which was generated on merc... more This review summarizes and synthesizes the significant amount of data which was generated on mercury (Hg) and persistent organic pollutants (POPs) in Canadian Arctic marine biota since the first Canadian Arctic Contaminants Assessment Report (CACAR) was published in 1997. This recent body of work has led to a better understanding of the current levels and spatial and temporal trends of contaminants in biota, including the marine food species that northern peoples traditionally consume. Compared to other circumpolar countries, concentrations of many organochlorines (OCs) in Canadian Arctic marine biota are generally lower than in the European Arctic and eastern Greenland but are higher than in Alaska, whereas Hg concentrations are substantially higher in Canada than elsewhere. Spatial coverage of OCs in ringed seals, beluga and seabirds remains a strength of the Arctic contaminant data set for Canada. Concentrations of OCs in marine mammals and seabirds remain fairly consistent 0048-9697/$ -see front matter D

Journal of Applied Ecology, 2002

Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled ... more Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled with contaminant analysis, stable isotope analysis has also been used for tracing the pattern and extent of biomagnification of contaminants in aquatic food webs. 2. Combined analysis of nitrogen ( δ 15 N) and carbon ( δ 13 C) isotopes from fish species in a sub-Arctic lake were related to tissue mercury (Hg) concentrations to assess whether carbon sources influenced Hg accumulation in fish, in addition to trophic position. 3. Statistical models were used to estimate Hg biomagnification and uptake, to elucidate Hg accumulation dynamics and to appraise the relative importance of Hg exposure routes for the fish species. 4. Species Hg contamination increased as a function of trophic position ( δ 15 N) and was inversely related to the δ 13 C signature. Species connected to the benthic food chain had lower Hg concentrations than species connected to the pelagic food chain. Species undergoing ontogenetic dietary shifts with increasing size, e.g. lake trout Salvelinus namaycush , also showed increased Hg concentrations with increasing reliance on pelagic fish as prey.

Science of The Total Environment, 2015

More than half of childbearing-age women in Nunavik have at-risk blood Hg levels.

Science of The Total Environment, 2015

Temporal trends in perfluoroalkyl compounds (PFCs) were investigated in liver samples from two ri... more Temporal trends in perfluoroalkyl compounds (PFCs) were investigated in liver samples from two ringed seal (Phoca hispida) populations in the

Environmental Toxicology and Chemistry, 2014

Science of The Total Environment, 2005

Mercury (Hg) and cadmium (Cd) concentrations in ringed seal liver and kidney were compared from 1... more Mercury (Hg) and cadmium (Cd) concentrations in ringed seal liver and kidney were compared from 11 locations across the Arctic, from Alaska, Canada, Greenland, Svalbard to the White Sea. Adult and sub adult seals were evaluated separately to account for age accumulations of Hg and Cd. Only recently (1995-2001) collected samples were included to minimize influence of changes over time. The Hg and Cd concentrations in ringed seal liver and kidney differed significantly among the studied locations. The Hg concentrations in liver of ringed seals was highest in the western Canadian Arctic locations, while Cd in liver was highest in the eastern Canadian and West Greenland locations. In general, Hg and Cd concentrations in liver and kidney were significantly higher in adult ringed seals than in sub adults and the circumpolar patterns were most pronounced in adult ringed seals. The Hg and Cd concentrations in kidney of ringed seals in general supported the geographical pattern found in livers although the coverage was more limited. The most likely explanation for the observed circumpolar pattern appears mainly to be related to natural geological differences in mineral (Hg and Cd) among regions.

Journal of Toxicology and Environmental Health, Part A, 2006

have been reported in marine mammals on a global scale. While risk assessments are generally base... more have been reported in marine mammals on a global scale. While risk assessments are generally based on quantifying body burdens of toxicants, much less is known about associated adverse health effects and their underlying mechanisms. The purpose of this study was to characterize the inhibitory effects of methylmercury (MeHg + ), mercuric chloride (Hg 2+ ), p,p¢-DDT, Arochlor 1254, chlordane, dieldrin, lindane, and toxaphene on [ 3 H]quinuclidinyl benzilate ([ 3 H]-QNB) binding to the muscarinic cholinergic (mACh) receptor in cellular membranes isolated from the cerebrum of ringed seals (Phoca hispida). [ 3 H]-QNB binding to the mACh receptor was saturable with a mean receptor density (B max ) of 826.9 ± 68.4 fmol/mg and ligand affinity (K d ) of 0.31 ± 0.04 nM. MeHg + and Hg 2+ were the only neurotoxicants that inhibited radioligand binding by greater than 50%. Hg 2+ was significantly more potent at inhibiting mACh receptor binding than MeHg + when the IC 50 data were compared (IC 50 = 1.92 ± 0.06 mM versus 2.75 ± 0.22 mM), but when the data were normalized to derive inhibition constants (K i ) there was no statistical difference in inhibition (Hg 2+ = 1.38 ± 0.07 mM; MeHg + = 1.26 ± 0.12 mM ). Toxaphene also inhibited mACh receptor binding by 22.4%, but this was only significant at the highest concentration tested (320 mM). Overall, these data suggest that Hg, and not organochlorines, inhibits ligand binding to the mACh receptor. These mechanistic findings may be used to support and develop specific biomarkers of Hg exposure and neurotoxicity in sensitive ecological species.

Environmental Toxicology and Chemistry, 2007

The present study examined spatial trends of perfluoroalkyl compounds (PFCs) in liver samples fro... more The present study examined spatial trends of perfluoroalkyl compounds (PFCs) in liver samples from 11 populations of ringed seals (Phoca hispida) in the Canadian Arctic from 2002 to 2005. Trophic position and relative carbon sources were compared by analyzing stable nitrogen and carbon isotopes in muscle samples. Geometric mean concentrations of total C 9 -C 15 perfluorinated carboxylates (PFCAs) ranged from 8.8 to 84 ng/g wet weight, and C 9 -C 11 PFCAs predominated. Perfluorooctane sulfonate was the dominant PFC measured, with concentrations ranging from 6.5 to 89 ng/g wet weight, contributing between 29 and 56% of the total PFC concentration. Overall, mean PFC concentrations were similar between populations, and differences were attributed largely to elevated levels in the Gjoa Haven (Rae Strait, central Canadian Arctic archipelago) and Inukjuak populations (eastern Hudson Bay) and to lower concentrations at Pangnirtung (Cumberland Sound, Baffin Island). Mean stable nitrogen isotope ratios (Ϯ95% confidence intervals) ranged from 14.7‰ (Ϯ0.3‰) at Nain (Labrador) to 17.9‰ (Ϯ0.7‰) at Gjoa Haven, suggesting that all populations were within the same trophic level. Stable carbon isotope ratios varied widely between the seal populations, ranging from Ϫ22.9‰ (Ϯ0.2‰) at Gjoa Haven to Ϫ17.7‰ (Ϯ0.4‰) at Nain. The ␦ 13 C ratios from Gjoa Haven were significantly more depleted than those for other populations and may suggest a terrestrially based carbon source. The depleted stable carbon isotope ratio may explain the elevated PFC concentrations in the Gjoa Haven population. Analysis of covariance indicated that ␦ 13 C was a significant covariable for seven of nine seal populations for which ␦ 13 C values were available. After adjusting for ␦ 13 C values, concentrations of most PFCs generally were statistically greater in the Grise Fiord, Qikiqtarjuaq, Arviat, and Nain populations.

Environmental Science & Technology, 2007

Polybrominated diphenyl ethers (PBDEs) were determined in adipose tissue of adult and subadult fe... more Polybrominated diphenyl ethers (PBDEs) were determined in adipose tissue of adult and subadult female polar bears sampled between 1999 and 2002 from sub-populations in Arctic Canada, eastern Greenland, and Svalbard, and in males and females collected from 1994 to 2002 in northwestern Alaska. Only 4 congeners (BDE47, 99, 100, and 153) were consistently identified in all samples. BDE47 was the major PBDE congener representing from 65% to 82% of the sum (Σ) PBDEs. Age was not a significant covariate for individual PBDEs or ΣPBDE. Higher proportions of BDE 99, 100, and 153 were generally found in samples from the Canadian Arctic than from Svalbard or the Bering-Chukchi Sea area of Alaska. Geometric mean ΣPBDE concentrations were highest for female polar bear fat samples collected from Svalbard (50 ng/g lipid weight (lw)) and East Greenland (70 ng/g lw). Significantly lower ΣPBDE concentrations were found in fat of bears from Canada and Alaska (means ranging from 7.6 to 22 ng/g lw).

Environmental Research, 2012

Methylmercury (MeHg) is a neurotoxicant that has been found at elevated concentrations in the Arc... more Methylmercury (MeHg) is a neurotoxicant that has been found at elevated concentrations in the Arctic ecosystem. Little is known about its internal dose in wildlife such as polar bears. We measured concentrations of mercury (Hg) in three different brain regions (cerebellum, frontal lobe and brain stem) of 24 polar bears collected from the Nunavik, Canada between 2000 and 2003. Speciation of Hg was measured by High Performance Liquid Chromatography coupled to Inductively Coupled Plasma Mass Spectroscopy (HPLC-ICP-MS). Concentrations of mean total Hg in brain tissue were up to 625 times lower (0.28 7 0.07 mg kg À 1 dry weight (dw) in frontal lobe, 0.237 0.07 mg kg À 1 dw in cerebellum and 0.12 7 0.03 mg kg À 1 dw in brain stem) than the mean total Hg concentration previously reported in polar bear liver collected from Eastern Baffin Island. Methylmercury (MeHg) accounted for 100% of the Hg found in all three brain regions analyzed. These results suggest that polar bear might reduce the toxic effects of Hg by limiting the uptake into the brain and/or decrease the rate of demethylation so that Hg can be excreted from the brain more easily. The toxicokinetics and the blood-brain-barrier mechanisms of polar bears are still unknown and further research is required.

Environmental monitoring and assessment

In order to evaluate the use of zebra mussels as biomonitors for metal bioavailability in the St.... more In order to evaluate the use of zebra mussels as biomonitors for metal bioavailability in the St. Lawrence River, we tested the hypothesis that the concentrations of 11 metals in zebra mussels vary significantly between sites along the river and that the season of collection and body size affect metal bioaccumulation. Mussels were collected at 14 sites during June 1996 and at monthly intervals at one site. Specimens were grouped in three size classes and their soft tissue was analyzed for As, Ca, Cd, Cr, Hg, Mn, Ni, Pb, Se, and Zn. Significant size effects were found for Ca, Cd, Cr, Cu, Ni and Zn. Spatial and seasonal variations in bioconcentration were significant for all metals. Spatial patterns in contamination that corresponded to known point sources of pollution or hydrology of the river were identified by principal component analysis. Seasonal variations can be attributed to the reproductive cycle of mussels and hydrological variability of the river. In comparison with values ...

Science of The Total Environment, 2005

This review summarizes and synthesizes the significant amount of data which was generated on merc... more This review summarizes and synthesizes the significant amount of data which was generated on mercury (Hg) and persistent organic pollutants (POPs) in Canadian Arctic marine biota since the first Canadian Arctic Contaminants Assessment Report (CACAR) was published in 1997. This recent body of work has led to a better understanding of the current levels and spatial and temporal trends of contaminants in biota, including the marine food species that northern peoples traditionally consume. Compared to other circumpolar countries, concentrations of many organochlorines (OCs) in Canadian Arctic marine biota are generally lower than in the European Arctic and eastern Greenland but are higher than in Alaska, whereas Hg concentrations are substantially higher in Canada than elsewhere. Spatial coverage of OCs in ringed seals, beluga and seabirds remains a strength of the Arctic contaminant data set for Canada. Concentrations of OCs in marine mammals and seabirds remain fairly consistent 0048-9697/$ -see front matter D

Journal of Applied Ecology, 2002

Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled ... more Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled with contaminant analysis, stable isotope analysis has also been used for tracing the pattern and extent of biomagnification of contaminants in aquatic food webs. 2. Combined analysis of nitrogen ( δ 15 N) and carbon ( δ 13 C) isotopes from fish species in a sub-Arctic lake were related to tissue mercury (Hg) concentrations to assess whether carbon sources influenced Hg accumulation in fish, in addition to trophic position. 3. Statistical models were used to estimate Hg biomagnification and uptake, to elucidate Hg accumulation dynamics and to appraise the relative importance of Hg exposure routes for the fish species. 4. Species Hg contamination increased as a function of trophic position ( δ 15 N) and was inversely related to the δ 13 C signature. Species connected to the benthic food chain had lower Hg concentrations than species connected to the pelagic food chain. Species undergoing ontogenetic dietary shifts with increasing size, e.g. lake trout Salvelinus namaycush , also showed increased Hg concentrations with increasing reliance on pelagic fish as prey.

Science of The Total Environment, 2015

More than half of childbearing-age women in Nunavik have at-risk blood Hg levels.