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Research Abstracts

The effect of chronic chromium exposure on the health of Chinook Salmon (Oncorhynchus tshawytscha).

by Aida M. Farag, Thomas May, Gary D. Marty, Michael Easton, David D. Harper, Edward E. Little, Laverne Cleveland  

Aquatic Toxicology, Vol. 76, pp. 246-257, 2006


This study was designed to determine fish health impairment of Chinook salmon (Oncorhynchus tshawytscha) exposed to chromium. Juvenile Chinook salmon were exposed to aqueous chromium concentrations (0-266 microgram/liter) that have been documented in porewater from bottom sediments and in well waters near salmon spawning areas in the Columbia River in the northwestern United States. After Chinook salmon parr were exposed to 24 and 54 micrograms Cr per liter for 105 days, neither growth nor survival of parr was affected. On day 105, concentrations were increased from 24 to 120 micrograms Cr per liter and from 54 to 266 micrograms Cr per liter until the end of the experiment on day 134. Weight of parr was decreased in the 24/120 micrograms Cr per liter treatment, and survival was decreased in the 54/266 micrograms Cr per liter treatment. Fish health was significantly impaired in both the 24/120 and 54/266 micrograms Cr per liter treatments. The kidney is the target organ during chromium exposures through the water column. The kidneys of fish exposed to the greatest concentrations of chromium had gross and microscopic lesions (e.g. necrosis of cells lining kidney tubules) and products of lipid peroxidation were elevated. These changes were associated with elevated concentrations of chromium in the kidney, and reduced growth and survival. Also, variations in DNA in the blood were associated with pathological changes in the kidney and spleen. These changes suggest that chromium accumulates and enters the lipid peroxidation pathway where fatty acid damage and DNA damage (expressed as chromosome changes) occur to cause cell death and tissue damage. While most of the physiological malfunctions occurred following parr exposures to concentrations > 120 micrograms Cr per liter, nuclear DNA damage followed exposures to 24 micrograms Cr per liter, which was the smallest concentration tested. The abnormalities measured during this study are particularly important because they are associated with impaired growth and reduced survival at concentrations >  120 micrograms Cr per liter. Therefore, these changes can be used to investigate the health of resident fish in natural waters with high chromium concentrations as well as provide insight into the mechanisms of chromium toxicity.


Preliminary examination of contaminant loadings in farmed salmon, wild salmon and commercial salmon feed.

by M.D.L. Easton, D. Luszniak and E. Von der Geest. 

Chemosphere, Vol. 46, pp. 1053-1074, 2002


This pilot study examined 5 commercial salmon feeds, 4 farmed salmon (1 Atlantic, 3 chinook) and 4 wild salmon (1 chinook, 1 chum, 2 sockeye) from the Pacific Coast for PCBs (112 congeners), polybrominated diphenylethers (PBDEs - 41 congeners), 25 organochlorine pesticides (OPs), 20 polycyclic aromatic hydrocarbons (PAHs), and methyl and inorganic mercury. The farmed salmon showed consistently higher levels of PCBs, PBDEs, OPs (except toxaphene) than the wild salmon The mean concentrations in pg/g were 51,216 vs 5,302 for total PCBs; 2,668 vs 178 for total PBDEs; 41,796 vs 12,164 for total OPs (except toxaphene). The farmed salmon levels are likely a consequence of the elevated level of contamination found in the commercial salmon feed (mean concentrations in pg/g were 65,535 for total PCBs; 1,889 for total BPDEs; 48,124 for total OPs except toxaphene). Except for a single high wild chinook value, PAHs were highest in the feed samples followed by the farmed fish and the 3 other wild fish. The Bio-Oregon-1996 feed of hatchery origin showed a level of PAHs ten times higher than any other feed. The genotoxic implications of such a high PAH level are considered for juvenile chinook salmon. Toxaphene and methyl mercury concentrations were not notably different between the wild and farmed salmon. There was no clear low contaminant brand of salmon feed. The human health implications of eating farmed salmon are considered from the perspective of the current WHO and Health Canada Tolerable Daily Intake values for PCBs. Based on a TDI of 1 pg TEQ/kg bw/day, this analysis indicated a safety concern for individuals who on a regular weekly basis consume farmed salmon produced from contaminated feed.


A Note on the Number of Morphometric Characters used in Fish Stock Delineation Studies Employing a MANOVA.

by R.K. Misra and M.D.L. Easton. 

Fisheries Research, Vol. 42, pp. 191-194, 1999


In a fish stock delineation study based on MANOVA/MANCOVA of a morphometric data set, use of measurements on many characters will result in a statistical artifact generating spurious significant differences between populations. A preliminary method is demonstrated for testing the presence of this artifact. Data analyzed for stock identification purposes should employ only a small number of morphometric characters, perhaps three or four.


A Comment on Analyzing Flow Cytometric Data for Comparison of Mean Values of the Coefficient of Variation of the G1 Peak.

by R.K. Misra and M.D.L. Easton.

Cytometry, Vol. 36, pp. 112-116, 1999


The coefficient of variation (CV) is often used to characterize and summarize the flow cytometry analysis of nuclear DNA of the Go/G1 peak in a cell population within an individual organism. CV values are frequently used in subsequent statistical analysis to compare experimental groups of individuals. We explain why the conventional analysis of variance, linear comparisons and regressions that employ the F and t tests are not appropriate for analyzing CV data sets. The weighted least squares procedure which utilizes the chi-square test is presented as an adequate method. We further explain why this type of data needs to be analyzed by this procedure. To illustrate the application of the weighted least squares procedure, we analyzed a real data set that had been previously analyzed by conventional methods. We found that a non-significant result (p=1) using the latter was significant when re-analyzed with the weighted least squares procedure (p=0.032). Significant differences between treatments established by the weighted least squares often go unidentified by the conventional analysis. Use of the weighted least squares procedure is recommended for analyzing CV data sets


Genotoxic Effect of Bleached Kraft Mill Effluent on Juvenile Chinook Salmon (Oncorhynchus tshawytscha) - Revisited.

by M.D.L. Easton, R.K. Misra and G.M. Kruzynski. 

Poster Presentation at US EPA NHEERL Workshop, Cary, North Carolina. 1998.


We present a re-analysis of previously published data from a field bioassay examining the genotoxic effects of effluent from a 100% chlorine dioxide bleached Kraft mill on juvenile chinook salmon (Oncorhynchus tshawytscha). The concentrations examined were 0%, 2%, 4%, 8% and 16% over a 30 day exposure. By the flow cytometry method with an enhanced data analysis, the red blood cells of the fish showed significant nuclear DNA damage starting at the 2% concentration level. In the 2-factor analysis of normoxic Vs hypoxic, the effluent concentration treatments examined were 0%, 4%, 8% and 16%, the 2% concentration group not being included because it was only available for the normoxic (85% air saturation) data set. The additional treatment of reducing air saturation levels to 65% (hypoxic) caused an increase in the observed degree of DNA damage at the 8% and 16% concentrations. The implications of somatic cell genotoxic damage for risk assessment is discussed.


Genetic toxicity of Pulp Mill Effluent on Juvenile Chinook Salmon (Oncorhynchus tshawytscha) Using Flow Cytometry.

by M.D.L. Easton, G.M. Kruzynski, I.I. Solar and H.M. Dye.

Water Science and Technology, Vol. 35, pp. 347-355, 1997.


On-site bioassays were conducted at the furthest upstream pulp mill on the Fraser River in British Columbia. Uncontaminated river water was used to dilute treated effluent as discharged from the final diffuser pond. A single cohort of juvenile (8-10gm) chinook salmon (Oncorhynchus tshawytscha) were divided into an hypoxic group receiving 65% oxygen saturated water and a normoxic group receiving ambient 88% oxygen saturated water. Both groups were exposed over a period of 30 days to effluent concentrations of 2%, 4%, 8%, and 16%, while the controls received uncontaminated river water. This range of concentrations spanned those encountered by wild juvenile salmon over-wintering in the upper Fraser River mainstem. The blood when analyzed by flow cytometry showed significant concentration-dependent clastogenic damage in both the normoxic and hypoxic groups starting at the 4% concentration. A concentration-response curve was determined from the hypoxic data set. Genetic implications of mutagenic damage to natural populations of chinook salmon is discussed along with the utility of the flow cytometer in detecting genotoxic damage.



Updated by Michael Easton 2009.