Fish and Heavy Metal Contamination

The heavy metal contamination of fish does not mean that the oceans are buzzing with the sound of salmon and tuna, head banging to AC/DC – although that would be a rather nice image!

Rather, it is the more serious issue of our marine life being poisoned by toxic levels of metals, which are then passed up the food chain.

What Are Heavy Metals?

Heavy metals such as zinc, iron, and copper are naturally occurring substances in the Earth’s crust. Some are needed by humans in trace amounts to maintain optimum body function, whilst others such as mercury, arsenic, and cadmium can be harmful. All metals can be toxic if levels are too high.

Why do Heavy Metals Contaminate Fish?

Marine animals such as fish are able to readily absorb metals and their bodies regulate to accommodate their presence. They are easily stored in fatty tissue and will bio-accumulate if the fish is exposed to further contamination.

Copper And Zinc

It has been found that the presence of copper in water affects the populations of fish even in very low doses. Metals such as copper and zinc can leach into water from the mining industry, via storm drains and from agricultural run-off from fields.

Although levels of these metals are monitored in water, at such low levels as 2 parts per billion they are considered almost too insignificant to worry about. However recent research has discovered that even at extremely low levels copper will disrupt the sense of smell of fish preventing them from detecting predators or recognising their eggs.

High levels of copper in humans can cause diarrhoea, stomach cramps, and vomiting.


There is currently triple the amount of mercury falling from the sky than at the time of the Industrial Revolution. It is also contaminating many areas as a result of unregulated gold mining.

The metal is absorbed by fish and other aquatic animals, and passed up the food chain to any other fish-eating species.

Scientists today are concerned that people who eat fish contaminated with mercury will be put at risk – particularly pregnant mothers and children as mercury poisoning has been shown to adversely affect brain development. However it is also being linked to a higher risk of heart disease and stoke in men as well as memory loss, and central nervous system damage.


Cadmium is a heavy metal which has been found in quite high quantities in larger fish like tuna and swordfish. This is because the metal accumulates over time and also because these fish are higher up in the food chain and so will be eating already contaminated prey.

Cadmium is very toxic to humans and has been linked to kidney disease, lung problems, and prostate cancer.

Should You Eat Fish?

Whilst it would be wise to watch the amount of fish you consume – especially if pregnant, there is also evidence from British scientists to support the theory that the health benefits of the beneficial nutrients from fish such as Omega 3 outweigh the negative effects of heavy metal contamination.