Suzanne’s Blog: Mercury Levels in Yukon Fish – Do I Need to Worry?

Burbot liver has been providing me with Vitamin D during the long Yukon winter. I know that fish tend to accumulate toxins from our water systems, especially predatory fish.  So I wondered, since I am consuming a fair amount of burbot liver this winter, do I need to worry about mercury levels and other contaminants such as PCB’s and DDT?

To my surprise I learned that, in fish, mercury accumulates in the muscle in levels much higher than in the liver.  This is the exact opposite of terrestrial animals such as caribou where mercury levels are higher in the liver compared to the meat.

Mercury levels in fish vary depending on the location but, in general, predatory fish (lake trout, burbot) have higher levels of contaminants than non-predatory fish (whitefish, grayling, salmon) and larger (older) fish have lower levels of contaminants than smaller (younger) fish.

According the limited burbot data we have available in the Yukon, the mercury levels in burbot muscle are five times higher than in the burbot liver.  However burbot muscle has the highest mercury levels of all the freshwater fish we catch in these parts. Chum salmon has the lowest mercury levels (less than a tenth that of burbot).

Based on Health Canada’s tolerable daily mercury limit is 0.47 ug/kg/day (for adult men and adult women who are not of child bearing age), my daily limit of burbot would be maxed out at 45 grams (1.5 oz) per day!  And my daily limit of burbot liver would be a whopping 225 grams (8 oz) per day. So my Vitamin D needs of 10 grams of burbot liver per day are no big deal.

But a daily limit of 45 grams of burbot muscle is a really small portion!  Of course, I am not eating burbot every day, so it still averages out ok – but it was a good reminder to limit my consumption of burbot.

So my take home message:  Burbot liver is a great source of local Vitamin D.  By consuming sautéed burbot liver one can get enough Vitamin D without too much mercury.   Burbot flesh should be considered a winter treat and if one is going to eat a lot of local fish, grayling and salmon would be better choices.

Want the stats? Here are the statistics from fish in Old Crow from a study by Yukon Research Scientist, Mary Gamberg Mercury per gram of fresh fish:

• Burbot : 0.62 ug/g
• Pike: 0.17 ug/g
• Burbot liver:  0.124 ug/g
• Grayling: 0.06 ug/g
• Chum Salmon: 0.04 ug/g

(Based on a sample size of 14 burbot, 11 pike and 12 chum salmon from Old Crow and grayling from other Yukon locations.) For adults, the tolerable daily mercury limit is  0.47 ug/kg/day (Health Canada)  (less for women of child bearing age) This translates to a tolerable daily limit in grams of fish for an adult woman of my size:

• Burbot : 45 g  (1.5 oz)
• Pike: 164 g
• Burbot liver: 225 g
• Grayling: 466 g
• Chum Salmon: 700 g

As mercury levels differ from one water system to another, I was curious as to what the levels would be in the burbot living in the Yukon River at Dawson City.  I sent in one 4 pound, 11 year old burbot for testing and levels came back as 0.23 ug/g mercury in the muscle and 0.04 ug/g in the liver.

The mercury levels from the Old Crow burbot are 2.5 times higher than the levels in the one fish tested from the Yukon River.  One sample only, but it suggests that the mercury levels in the Yukon River near Dawson are less than the levels around Old Crow. For PCB’s and DDT, the amount found in 10 grams of burbot liver from the Old Crow study was quite low, one tenth of the tolerable daily intake for PCB’s and one twentieth for DDT.