This year, worries of food poisoning via shellfish toxins have been on the rise, and so have the number of victims.
Shellfish sold on the market are completely safe, but caution is required when harvesting shellfish on one's own. The dangers of harvesting clams and other shellfish unattended is hardly known, and among the dangers are even some shellfish with toxins on the level of chemical weapons, experts warn.
Shellfish like Japanese littleneck clams and oysters are not poisonous on their own. They become poisonous when they absorb toxic plankton. According to the Ministry of Agriculture, Forestry and Fisheries (MAFF), there have only been between 10 and 37 cases annually of independently harvesting shellfish exceeding the regulated level of toxins over the last 10 years. However, that number has already exceeded 60 cases this year alone.
In March, a man in his 70s in Akashi, Hyogo Prefecture, ate a common mussel that he found at the mouth of a river in the city. He was later hospitalized for vomiting.
A leading expert on biotoxins like those found in shellfish and puffer fish, Tokyo Healthcare University professor Tamao Noguchi, lists the paralytic neurotoxin saxitoxin as a representative poison found in shellfish. "It's about as dangerous as the contents of a chemical weapon," he says.
The amount needed to lethally paralyze a person is only 0.5 milligrams. It is within the realm of possibility to kill 10,000 people with one 5-gram spoonful of saxitoxin. Even ingestion in small doses causes numbness and a burning sensation, and a person may become unable to move, and in the worst-case scenario, die from suffocation from paralysis of the lungs. It is no wonder that the Ministry of Economy, Trade and Industry's chemical weapon and narcotic drug supply control measures office strictly regulates the production and extraction of the toxin under the Act on the Prohibition of Chemical Weapons and the Regulation of Specific Chemicals.
According to the Cabinet Office Consumer Affairs and Food Safety Committee and other organizations, the first recorded paralysis by shellfish toxins was a case involving Japanese littleneck clams in Toyohashi, Aichi Prefecture, in 1948. The danger was not well understood at the time, but through the work of Noguchi and other scientists in the 1970s, an explanation for the phenomenon progressed. In the 1980s, the then Ministry of Health and Welfare (now the Ministry of Health, Labor and Welfare) set regulatory levels on shellfish toxins, and created a system for screening the animals before they became meals. Since then, there have been virtually no cases of food poisoning via clams and other bivalves sold in the marketplace.
However, there have been cases of poisoning as a result of people harvesting the shellfish on their own. In Hokkaido in 1979 and Aomori Prefecture in 1989, there were cases of one person dying after eating common mussels, respectively.
Aside from paralytic toxins, there are also shellfish poisons that cause memory loss. In Canada in 1987, over 100 people got food poisoning from common mussels, and four people died while 12 were left with damage to their memory. There are also toxins that cause diarrhea, but that rarely leads to death.
The shellfish sold in shops are almost completely safe. The danger really comes down to self-harvesting the animals.
"Nothing can be done except continuing to sound the alarm," says Noguchi. "There are toxins in the natural world. Possessing accurate knowledge and having the correct amount of caution is of the utmost importance."
The amount of toxins contained in shellfish changes along with environmental conditions, and government bodies investigate and make information about the poisons public.
"When going out clam digging or engaging in other shellfish collecting activities, I would like people to definitely check that information first," Noguchi advises.
(Japanese original by Tatsuya Kishi, General Digital News Center)