Dec 07 2008
Heavy Metal Fish!
Well, my last post How Healthy is Milk?, gave the dairy industry a tongue lashing and maybe got the message across that milk isn’t all its cracked up to be. In this post, I’m turning a baleful eye towards the seas in a look at another of our sources of nourishment, fish.
On the surface of it, fish caught in the oceans of the world must appear to be the least affected by our polluting ways and in many cases this is true. But there are some fish, especially those that sit near the top of the food chain, that are not quite as healthy as they appear.
Tuna is one such offender when it comes to providing us with more than we were bargaining for in the form of elevated levels of mercury. This happens because tuna, like many other carnivorous fish, sit high in the food chain. That means that they eat other big fish, which in turn have eaten smaller fish, which have eaten still smaller fish and so on. The small fry at the other end of the food chain will pick up mercury from our polluting ways, as they filter the waters for nutrients and scavenge for food on the sea bed, where they will encounter the highest levels of mercury and other heavy metals.
Larger predators eat them and inherit their load of unwanted heavy metals, because the fish’s digestive system cannot expel them, in a similar way to us humans. So the levels of heavy metals such as mercury, aluminium and lead can only increase in the body. Of course, the more mercury laden prey each fish eats, the more they contain themselves, which is passed on right up through the food chain until it finds its way into the larger fish that our trawlers catch for our consumption.
Bearing this in mind, the official WHO recommendations for adults, is that we should eat no more than two portions of tuna per week. That goes for other predatory fish as well. In future posts I’ll be looking more at the health aspects fish in our diets.
