The reason why China has imposed a ban on importing shellfish from Northern California and the rest of the West cost is because recent shipments of a type of shellfish known as geoduck clams were found to contain high levels of arsenic along with another toxin that's the cause of paralytic shellfish poisoning. The restriction is indefinite and applies to all shellfish known as two-shelled bivalves, including oysters and clams, harvested from the waters off the coast of Northern California, Oregon, Washington, and Alaska.
It also puts thousands of divers out of work. Many of the divers who look for shellfish in those areas are Native Americans, for example Puget Sound's Suquarmish Tribe. No one knows how long the closure will last, according to the ENews article, "Unprecedented’: China bans all imports of shellfish from U.S. West Coast — Official: “They’ve never done anything like that that I’ve ever seen” — Includes Washington, Oregon, Alaska and N. California — Gov’t says it will continue indefinitely." Or see, "China Imposes First-Ever West Coast Shellfish Ban" and "China bans shellfish imports from US West Coast - Huffington Post." The Sacramento Bee also reprinted an Associated Press article December 15, 2013 about the ban on shellfish, "China Bans West Coast Shellfish Imports," as did CNS News. You can check out, "China bans shellfish imports from US West Coast."
Various states have people monitoring toxins in shellfish for the Departments of Health in each of the states that deal with shellfish. At present China is not allow shellfish to be imported from the entire area based on potentially two areas or maybe just one area. On the other hand, scientists testing the shellfish still don't know yet all the areas where the toxic shellfish are being found because they aren't done with testing.
Last year the U.S. exported more than half a billion dollars worth of shellfish – with China as its biggest customer. This year, China doesn't want any shellfish from the USA. Then again, according to the Department of Health, shellfish already on the market for sale in the U.S. are safe to eat. The biggest worry of consumers is whether anyone is asking the government "are you really sure"?
Risk to consumers from fungal toxins in shellfish should be monitored
To protect consumers, screening shellfish for fungal toxins is important, say scientists, according to a September 5, 2013 news release, "Risk to consumers from fungal toxins in shellfish should be monitored." Research, published September 6, 2013 in the Society for Applied Microbiology (SfAM) journal, Letters in Applied Microbiology, shows that in an area with contamination by strains of Penicillium fungus, bivalve molluscs (clams, oysters, mussels, scallops, etc.) will contain toxins at much higher levels that are found in the surrounding environment.
Professor Yves François Pouchus, from the University of Nantes, France, led the research, explaining, according to the news release, "A high level of toxins in the shellfish tells us that we have to be careful not to underestimate the impact of certain Penicillium strains in the water where shellfish are harvested for human consumption." Professor Pouchus' team have found that the fungi actually produce more toxin when growing inside mussels or in a medium containing mussel extract.
Although toxins from Penicillium don't cause acute food poisoning, they can have a negative impact on cells and DNA. In theory, these mycotoxins could cause health issues in the long term, such as cancer. Pouchus concludes, according to the news release, "At this point, we think it would be pertinent to begin screening edible shellfish for mycotoxins in order to protect consumers."
Paralytic shellfish toxins cause mutation that allows clams to accumulate 100 times more toxin
Exposure to toxins that cause paralytic shellfish poisoning can result in a mutation that makes clams much more resistant to the toxin than other clams, making them more dangerous to humans, according to a study published the week of April 6, 2005 in the journal Nature. Paralytic shellfish toxins (PSTs) are produced by algae that appear in certain coastal areas in the United States in an event known as an algal bloom, commonly called a "red tide." People who eat clams exposed to the PSTs can suffer the paralytic effects of the toxins, and there is no cure for the poisoning, according to the April 6, 2005 news release, "Paralytic shellfish toxins cause mutation that allows clams to accumulate 100 times more toxin."
Researchers found that softshell clams in areas frequently affected by harmful algal blooms are more resistant to paralytic shellfish toxins (PSTs) than clams from other areas. They knew from earlier work that the toxins block the function of the sodium ion channel, a molecular switch that generates the nerve impulse and therefore is vital to neural and muscular activity. What they did not know was why some clams were more resistant than others.
The collaborative team of scientists from Washington, Maine, and Nova Scotia determined that the toxins cause a small mutation that prevents them from binding to the sodium ion channels in the clam's nerve tissue. Instead of binding to the ion channels and causing paralysis and later death, the toxins build up in the clam, accumulating about 100 times more toxin than in clams without the mutation. The resistance allows them to continue feeding during the harmful algal bloom and accumulate levels of toxins that increase risk of paralytic shellfish poisoning in humans.
Scientists and public health officials knew that clams carrying the toxins could survive after an algal bloom, which is why clams are tested well after a "red tide" event to reduce the risk of poisoning in humans. But no one knew until now why the clams were accumulating the toxins.
"It is quite surprising that the toxins could serve as selective agents for a mutation in the sodium ion channel, and that the mutation can prevent toxin binding without otherwise changing the function of the ion channel," explains Dr. William Catterall, according to the news release. Catterall is a professor and chair of pharmacology at the University of Washington School of Medicine in Seattle, and one of the paper's co-authors.
A collaborative team of scientists from the University of Washington and the National Oceanic and Atmospheric Administration Northwest Fisheries Science Center in Seattle, the University of Maine, and the Institute for Marine Biosciences in Halifax, Nova Scotia conducted the research. Scientists hope that identifying this mutation will help them develop a genetic marker for breeding shellfish stocks that accumulate little or no paralytic shellfish toxins (PSTs) in regions affected by harmful algal blooms, thereby reducing paralytic shellfish poisoning incidents and clam harvest losses.
Warning lights mark shellfish that aren't safe to eat: Beware of red tide and similar blooms
Red tides and similar blooms can render some seafood unsafe to eat, though it can be difficult to tell whether a particular batch harbors toxins that cause food poisoning, according to a December 15, 2010 news release, "Warning lights mark shellfish that aren't safe to eat." A new kind of marker developed by chemists at the University of California - San Diego, and reported in the journal Chemical Communications makes it easier to see if shellfish are filled with toxin-producing organisms.
Mussels and oysters accumulate single-celled marine creatures called dinoflagellates in their digestive systems as they filter seawater for food. Usually dinoflagellates are harmless, but sometimes they produce dangerous toxins. The trick is figuring out when. Scientists think symbiotic bacteria that live on the surface of dinoflagellates probably help synthesize the toxins, but no one is sure how. Genetic tools often used to sort out such relationships don't work for dinoflagellates, which have enormous genomes that are not well understood.
So chemistry professor Michael Burkhart's group took a different approach. They set up a system to add a fluorescent tag to an enzyme that makes one kind of toxin, okadaic acid, but with a twist. By handing the tag to a the molecule that turns the enzyme on, they ensured that only those parts of cells that are capable of making the toxin would glow.
Specks glow brightly on the surface of dinoflagellates incubated with both the marker and symbiotic bacteria, and the toxin accumulates in the culture. Those lights go off, and toxin production ceases, if the chemists add antibiotics to the mix.
The new marker proved useful in live mussels as well. Their guts glowed with toxin-producing dinoflagellates even before the poison transferred to the mussel tissue itself.
This technique may could be the basis of an early warning system for aquaculturists and in theory it could lower the risk of shellfish poisoning. At the time of the news release in 2010, the method required a relatively expensive fluroscence microscope to view the tagged cells, but Burkhart's team is optimistic that rapidly developing technology will soon make the tag easy to detect with a handheld device. The National Institute of General Medical Science and the American Chemical Society funded this project.