In May of this year I diaried about a published report by a group of researchers from Nagasaki University and the University of the Ryukyus documenting serious biological impacts on the larvae of the pale grass blue butterfly due to ingestion of radioactive contamination from the Fukushima Daiichi disaster on leaves that comprise their diet. In that study, the internal doses of the larvae was relatively high, using leaves gathered inside the evacuation zone and from selected places farther away but still in the plume pathways.
In that Nature publication, the researchers documented an LD50 - the calculated level of internal exposure at which 50% of the exposed population dies - at just under 2 becquerels per individual, from cesium [134 and 137].
The same researchers have published a follow-up research article on BioMed Central [BMC Evolutionary Biology 2014, 14:193; September 23, 2014; open access] documenting damage to the same species from a cesium contaminated diet at lower levels of chronic exposure and over two generations:
Ingestion of radioactively contaminated diets for two generations in the pale grass blue butterfly
Conclusions
Biological effects are detectable under a low ingested dose of radioactivity from a contaminated diet. The effects are transgenerational but can be overcome by ingesting a non-contaminated diet, suggesting that at least some of the observed effects are attributable to non-genetic physiological changes.
[my emphasis]
This time the researchers collected host plants from six areas of Japan with lower levels of contamination, at distances from the Daiichi facility of 59 to 1760 kilometers. The leaves used for the May study were contaminated with thousands of Bq/kg. These leaves carried cesium contamination that ranged from 0.2 to 161 Bq/kg, much lower levels.
From Science Magazine:
The new study shows that radiation can damage larvae even at much lower concentrations. ... "These results suggest that low-dose ingestion of approximately 100 Bq/kg may be seriously toxic to certain organisms," the team writes...
But that's not all they found...
In another experiment, the researchers divided offspring [of the least damaged among the original test generation] of the butterflies into two groups, feeding the larvae either the same contaminated leaves their parents had eaten or uncontaminated leaves. Larvae fed the contaminated leaves had even lower survival rates and more abnormalities than their parents, whereas those feeding on clean leaves largely reverted to near-normal in both mortality rates and frequency of abnormalities.
Who'da thunk? Once you remove the exposure agent (don't eat/drink the contamination), the test subjects got healthier! Duh.
Of course, humans are not butterflies, and we are known to tolerate much higher levels of toxic, carcinogenic and mutagenic substances than insects can. Still, you'll see that insecticides in this country come with warning labels about the chemicals and toxins they contain, a product of what's called the "precautionary principle" that government regulators have long applied to harmful substances. And we are all familiar with harmful substances used in the past that were or are still present as environmental contaminates. DDT, PCBs, Dioxin, asbestos, various petrochemicals, etc., plus a host of unpronounceable nasties we hear about whenever there are suspicious "cancer clusters" and/or class action suits. Even after approval for marketing, the FDA and EPA are known to come along with bans and restrictions later when a drug or food additive or chemical/compound proves to be more harmful than the manufacturers estimated when they got approval. Even though the government is perfectly willing to accept a certain number of public deaths they know will be caused, if the 'benefit' to the corporation, government and/or larger public is deemed to outweigh those. Always a bottom line calculation.
Strangely, this "precautionary principle" doesn't seem to apply to much of anything nuclear. That's probably because the erstwhile regulators in nuclear governments as well as the UN [IAEA] consider their mandate to promote nuclear technology and the industry to be more important than their sub-mandate to protect the public from the harm radiation is known to cause.
It should also be known that the cesium is by no means the only dangerous radionuclide released into the environment from the disaster at Daiichi, or even THE most dangerous radionuclide released. It's just the most prevalent in Japan at this point in time. Internal contamination from less abundant radionuclides can be more dangerous at lower levels.
So it doesn't hurt to keep in mind when looking at evidence that chronic low-dose radiation causes real harm, that Japan's regulatory limit for radioactive contamination in human food is 100 Bq/kg. Conversely, the limit here in the United States is 1,200 Bq/kg. That's something to think about, in light of how much effort is going into the project of convincing the American public to disregard and/or dismiss the idea of biological harm caused by the ongoing Daiichi disaster. If a food (like rice, seaweed, tea, vegetables, fruit, fish, meat and dairy) produced in Japan is deemed far too contaminated for the Japanese to eat, they can always just sell it to us. Sort of helps spread things around a bit...
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Phys.Org's take on the latest research:
Food affected by Fukushima disaster harms animals, even at low levels of radiation
Reduced vitamin A (retinol) levels indicate radionuclide exposure in Streaked Shearwaters (Calonectris leucomelas) following the 2011 Fukushima nuclear accident
Morphological abnormalities in gall-forming aphids in a radiation-contaminated area near Fukushima Daiichi: selective impact of fallout?