It’s enough to make members of the Sea Shepherd Conservation Society choke on their tofu burgers. Stocks of frozen whale meat in Japan have reached 4,000 tons — that’s 4 million kg.

Let’s assume that 100 grams is a reasonable meal-size portion. That means there are about 40 million portions of whale meat being expensively stored under refrigeration ready for eating.

But not enough people eat kujira (whale), and far from dwindling, Japan’s whale mountain is growing. It’s just not popular enough as a food.

The Institute of Cetacean Research (ICR) — a branch of the government’s Fisheries Agency that outsources and oversees Japan’s whaling operations — urgently needs to reduce the size of the mountain. It wants us to eat more whale, and it has targeted school children as important consumers.

As I write, conservationists are gathering in Taiji, Wakayama Prefecture, as the annual oikomi (drive fishery) for dolphins is set to get under way. Both the so-called fishermen and supporters of whaling are closely guarding the notorious killing cove. But today’s column isn’t about the politics of whaling or the suffering of cetaceans. I want to look at what we know about how safe whale meat is to eat. This is particularly important if it is being served to children.

In providing whale meat for schools, the ICR’s stated aim is to teach children about what it sees as a traditional part of Japanese food culture. To that end, the institute makes whale meat available to schools for one third of the market price. The ICR wants to retro-fit a nostalgia and foster a love for whale meat among the young — and to try to ensure they remain consumers of whale meat when they grow up.

Whale meat has been eaten for centuries in Japan, even millennia, but it was not consumed on a large scale until after World War II. Post 1945, as the country was being rebuilt, whale meat became an important source of protein. The children who ate it in their school lunches back then are now the venerable policymakers in the ICR and in government.

According to a survey released last month of 29,600 public elementary and junior high schools in Japan, 18 percent said they had served whale meat to children at least once in the fiscal year to March 2010.

I’m sure eating one portion of whale meat isn’t going to do anyone any harm — but what is known about the health effects?

The first potential problem with whale meat concerns its possible contamination with mercury, a harmful heavy metal.

Mercury exists in different chemical forms. The kind most relevant here is organic mercury, particularly methyl mercury. This is the form that builds up in whale meat.

A study conducted by Tetsuya Endo at the Health Sciences University of Hokkaido, and Koichi Haraguchi at the Daiichi College of Pharmaceutical Sciences in Fukuoka, investigated methyl mercury levels in whale meat on sale in Taiji, and in hair samples taken from 50 residents of the town. They found methyl mercury levels of 5.9 micrograms per gram in the red meat. For comparison, the United States Food and Drug Administration sets an “action level” of 1 microgram. In the U.S., any food with more than 1 microgram of methyl mercury is not allowed to be sold or consumed.

As for the hair samples, in residents who often ate whale meat, on average their hair contained 24.6 micrograms of mercury per gram. The figure from residents who do not consume whale meat was 4.3 micrograms, and in the Japanese population as a whole the figure is about 2 micrograms. The study was published earlier this year in Marine Pollution Bulletin. (In case you want to look it up yourself, the Digital Object Identifier [DOI] reference to the paper is 10.1016/j.marpolbul.2009.11.020).

OK, so whale meat contains high levels of organic mercury, and people who eat whale meat themselves contain high levels of the metal. How harmful is this?

In the September 2010 issue of the journal Current Problems in Pediatric and Adolescent Health Care, a group of public health researchers made an extensive review of the evidence for the effect of mercury exposure on children’s health. “Mercury,” the team write, “is a highly toxic element; there is no known safe level of exposure. Ideally, neither children nor adults should have any mercury in their bodies because it provides no physiological benefit.” (Again, the DOI reference to the paper is: 10.1016/j.cppeds.2010.07.002.)

The team recommends prevention as the key to reducing mercury poisoning, which to my mind says: Don’t eat whale meat if you want to avoid ingesting and accumulating mercury. The researchers also point out that the development of the child in utero and early in life is at particular risk of mercury contamination.

Finally, there’s a paper in October 2010’s issue of Environmental Research (DOI: 10.1016/jenvres.2010.07.001). Researchers based at Tohoku University conducted a “birth cohort” study on almost 500 mothers-to-be, and the children they gave birth to. They looked at the amount of seafood consumed by the women, the amount of mercury in the women’s hair, and then they measured the child’s behavior at age 3 days using the standard Neonatal Behavioral Assessment Scale.

They found that the greater the amount of mercury in the mother’s hair, the worse the child performed on the behavioral test. “In conclusion,” the team write, “our data suggest that prenatal exposure to methyl mercury adversely affects neonatal neurobehavioral function.”

My conclusion from this would be not to eat lots of whale sashimi if you are pregnant. And my conclusion overall would be that, on health grounds alone, it is probably not advisable for children to eat whale meat at all.

Follow Rowan Hooper on Twitter at twitter.com/rowanns. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).’

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