Debating the Risk of Eating Fish Containing Mercury

From: Robina Suwol
Date: 28 Mar 2003
Time: 00:19:59
Remote Name:


Interpress Service

One in 12 North American women has enough mercury in her body to produce cerebral palsy, impaired memory and developmental delays in her unborn child, but scientists gathered here recently agreed those results should not stop people from eating fish - the main source of mercury.

A recent study found that people in San Francisco, Calif., who ate fresh fish - sushi in particular - three or four times a week developed numb hands, experienced hair loss and had children who were developmentally delayed, said David Carpenter, a professor of environmental health and
toxicology at the University of Albany in New York state.

"They were suffering from Minamata disease," said Carpenter. The disease, which is actually mercury poisoning, was first identified in 1955 when people in Japan's Minamata Bay consumed fish with high mercury concentrations due to local industrial sources.

Mercury is a potent neurotoxin and the people of Minamata Bay suffered blindness, paralysis, loss of muscular control, birth defects and more than 1,400 deaths.

The afflicted Californians had been eating fresh tuna, swordfish, king mackerel and shark, all of which have high levels of mercury.

Other people around the world suffer mercury poisoning. Some living along the Tapajos River in Brazil's Amazon Basin have suffered neurological impairment from eating fish from their river with high concentrations of mercury.

In Greenland, where levels of the metal in ringed seals and beluga whales have quadrupled in 25 years, 16 percent of people have mercury levels above the toxic threshold.

Medical experts agree that fish is one of the healthiest foods -loaded with protein and heart-healthy Omega 3 fatty acids. There is no question that fish can help prevent heart disease, Carpenter agrees, but fish containing mercury can negate those benefits depending on how badly they are contaminated.

Mercury is a naturally occurring metal found in cinnabar, and low levels of it seep into the environment from rocks and soils, and in volcanic eruptions. The use of mercury in thermometers, dental fillings, fluorescent
light bulbs, vacuum gauges, some pharmaceuticals and older batteries, along with industrial wastes from mining, cement kilns, the manufacture of chlorine, and coal power plants have added tens, if not hundreds of thousands of tonnes of mercury to the global environment.

A United Nations Environment Programme (UNEP) report released last month found 70 percent of mercury emissions of human origin come from the burning of coal and the incineration of waste, annually pumping 1,500 tonnes of the metal into the environment.

Technologies are available to reduce mercury emissions from power stations by about 80 percent but they are costly, added the report, 'Global Mercury Assessment'. But UNEP urged governments to introduce drastic mercury reduction programmes.

Mercury is an element, so it does not disappear or break down. Moreover, mercury particles are easily transported by air currents thousands of kilometers from where they were produced. As a result, virtually all fish contain traces of the metal.

Fish pick up methyl mercury, a form of the element that binds to the protein in their bodies, from microorganisms in oceans and lakes. As big fish eat little fish, they absorb the methyl mercury in their prey so that larger older fish, such as swordfish, shark, and tuna, carry more of the metal than other species like salmon and shrimp.

In February, the U.S. Environmental Protection Agency (USEPA) reported that eight percent of all U.S. women of childbearing age - five million in all had mercury levels high enough to potentially cause learning disabilities, including reduced IQ and problems with motor skills, in their unborn children.

The EPA recommends that women and children under the age of six limit their fish consumption and avoid certain species entirely.

"While there is more and more evidence that at low doses mercury has subtle effects on a developing child," said Laurie Chan, associate professor at McGill University's Centre for Indigenous Peoples' Nutrition in Montreal, "we have to be very careful about the real risks mercury poses".

"We don't want people to get the message that they shouldn't necessarily eat less fish." Public health officials have long recommended eating two meals of fish a week but most North Americans do not consume that quantity.

It is particularly important for aboriginal people in northern Canada to continue to eat fish and other wild foods, added Chan, because the switch in their diets from traditional foods to market-based ones has been much more hazardous to their health.

Skyrocketing rates of diabetes and heart disease are just two of the health impacts. "Market-based diets are a lot worse for aboriginals than eating fish or marine animals containing mercury or PCBs," according to Chan.

But they should minimize their exposure to contaminates by choosing species and the parts of the fish or animal that have the lowest contaminate levels, she added.

The general public should take a similar approach towards the fish they eat, Chan said. "The real issue for mercury is what fish and where?"

In North America, mercury levels in fresh-water fish are measured annually and warnings or fish advisories are issued. Nearly all large carnivorous fish, like lake trout, walleye, pickerel and pike have high mercury levels and the advisories warn against eating them. "These can be really dangerous
for children if eaten regularly and in quantity," said Carpenter.

But there is no way to know if fish bought in stores or served in restaurants is safe. No labeling standards exist and the same fish are often given different names. "Consumers have no assurance that these fish are not contaminated," said Carpenter.

Until proper regulations and an official guide to eating fish is in place, what should people do? Learn more about the fish you eat and apply Carpenter's rule of thumb: "Don't eat large carnivorous fish." Salmon are the exception, he says, but choose wild over farmed if possible because farmed salmon contain other contaminants.

Last changed: February 07, 2007