Many modern diseases that inflict the global population can be linked to the accumulation of heavy metals in the human body.

Humans do not just drop dead after ingesting these metals. Rather, death comes slowly as we are gradually poisoned,” says Associate Professor Dr Tong Soo Long of Universiti Malaya’s chemistry department.

Heavy metals are insidious because they tend to “bioaccumulate.” This means that small, seemingly harmless doses received over years may accumulate in the body, finally reaching toxic levels, which undermine biological functioning.

Certain metals weaken the immune system and cause the organism to be attacked by parasites.

This is the suspected cause for the tragic dying of the seal population in the North Sea,” says Dr Tong.

Bioaccumulation occurs because these chemicals are non-biodegradable and are readily absorbed into the body but excreted very slowly, if at all, because heavy metals bind strongly with proteins.

These characteristics prevent heavy metals from being flushed out of the body by urination.

In essence, the body acts as a filter removing and accumulating these chemicals from all the food or liquids that pass through,” says Dr Tong.

He says bioaccumulation of metals may be compounded in a food chain, as organism at the top of the food chain feeding on those at the lower rungs will eventually absorb higher concentrations of heavy metals.

Dr Tong says the accumulated levels can be 10 million times higher than environmental concentrations.

He cited a case: the presence of DDT in water may be as low as 0.000003 parts per million (ppm) but it has been demonstrated that through the food chain – from plank tonic algae to zooplankton to small fish the level may build up to as high as 20ppm in fish-eating birds at the top of the food chain.

“Complicating the situation is the synergistic effects where as many as a dozen or more contaminants occur simultaneously, and act together to produce even more lethal effects.”

The worry with heavy metal pollution is that it just does not disappear from the environment, Dr Jamal Hisham Hashim of Universiti Kebangsaan’s department of community health says.

The danger of a build-up of heavy metals in the environment is genuine as whatever that is put there will remain and circulate between various environment compartments for a long time,” he says.

In the United States, he says, lead poisoning continues to threaten children even though leaded gasoline was banned over 20 years ago.

Research showed that children were still exposed to lead in soil, where atmospheric lead has deposited.

Once in the body, most heavy metals remain there forever.

Cadmium for example, has a biological half-life (time required to excrete half of the heavy metals absorbed) of up to 30 years.

It is up to 20 years for lead, up to 30 hours for arsenic and between 35 and 100 days for mercury. (Mercury has an extremely long half-life of between 15 and 30 years in the central nervous system (CNS)*.

With heavy metals, one must look at the body-burden. Even minute levels of exposure, if received over a lifetime, could lead to chronic toxicity in the body,” adds Dr Jamal. He proposes a national biological monitoring of heavy metals in blood, hair and urine in children.

UPM environmental health scientist Dr Zailina Hashim believes cases of heavy metal related illnesses are under-reported because of a lack of awareness.

She says doctors might fail to recognize heavy metal poisoning as the symptoms could be as banal (common) as stomachaches, constipation and vomiting.

The damage might go unnoticed unless doctors or researchers specifically hunt for them,” says Dr Zailina who is with the department of nutrition and community health.

To assess the health impacts, she suggested an exposure and risk assessment study of heavy metals exposure from all media namely food, water and air. Such information can then be used to re-adjust current standards or permitted levels in food.

There are also doubts over standards specified in the Food Act 1983 and Food Regulations 1985 – are they low enough?

Dr Zailina says the cadmium limit of one part per million (ppm) may still be excessive considering that it is a suspected carcinogen.

Recent scientific data from developed countries also revealed that far smaller doses of heavy metals than previously understood could harm children.

*Recent updated information.

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