Wednesday, August 24, 2011

Natural mercury in fish

Most of the posts on this blog are about bacterial food poisoning, so this post is a change on two counts.

Mercury contamination of fish is usually associated with industrial pollution of rivers and estuaries.  William Ray, of Radio New Zealand, today reported that experts have suggested that the levels of mercury in trout in waterways around Totorua are so high, people should limit their intake to one trout per month.  (I wish I could catch so many!).

Rotorua is one of New Zealand's most famous geothermal areas and the experts have suggested that the mercury is from natural hydrothermal sources.  However, it appears that runoff from farms in the area may also be involved.  The nutrients washed into the rivers and lakes cause algal blooms, which lower the dissolved oxygen content of the water.  This in turn allows transfer of mercury from mud into the water, from whence it enters the food chain.

Perhaps the most infamous mercury poisoning occurred in the Japanese city of Minamata, which gave the name Chisso-Minamata disease to the resulting neurological syndrome.  The Chisso Corporation chemical factory released methyl mercury into the Minamata Bay and this highly toxic compound was accumulated by fish and shellfish.

The Rotorua trout have also accumulated mercury, but Dr. Ngaire Phillips from the National Institute of Water and Atmospheric Research points out that the recommendation for consumption of no more than one trout per month is based on a lifetime consumption.

Saturday, August 13, 2011

Listeria and bacon recall

I was just scanning the news and did a double take.  An Ontario company, Aliments Prince, S.E.C., has just recalled 380,000 lbs of bacon because of possible contamination with Listeria monocytogenes.  That's a lot of bacon!

It seemed to me that this was excessively cautious.  L. monocytogenes should not be found in a food product that has been processed in such a way that the bacteria should not survive, but the organism can occasionally be found in foods that have not been given a listericidal process.  So green leafy vegetables and other raw foods may occasionally contain L. monocytogenes.  The bacteria can be found in many parts of the environment, such as surface water, soil and decaying vegetation, and it's not surprising to find it turning up sometimes in raw foods.

On closer reading, it turns out that the FSIS found a sample of cooked diced bacon from Aliments Prince contained the bacteria.  This is a whole new ball game - the product could be expected to be consumed without further heating and thus could put at risk susceptible consumers.  See my post "Listeria Hysteria" for further information.

The company has done the right thing.  We can't avoid occasional low levels of contamination of raw foods by L. monocytogenes, but something has gone seriously wrong when we find it in cooked foods.  Either the process given was too mild, or, much more likely, the product has been recontaminated post processing.

Tuesday, August 9, 2011

Haemolytic Uraemic Syndrome

In the wake of infection by Shigatoxin producing Escherichia coli (STEC), some patients develop Haemolytic Uraemic Syndrome (HUS).  The recent outbreak of O104:H4 STEC in Europe resulted in an unusually high proportion of patients going on to develop the syndrome, some of whom succumbed to the infection.

Drew Falkenstein, an associate of Marler Clark law firm in Seattle, has written a very well informed article on HUS.  Rather than write another, I suggest that interested readers follow the link to Drew's posting on Food Poison Journal.