Wednesday, April 3, 2013

Trends in hypothyroidism among newborns after the Fukushima nuclear meltdown

Source: Open Journal of Pediatrics

Congenital hypothyroidism is a disorder that results in stunted growth, lowered intelligence, deafness, and neurological abnormalities, but can be effectively treated if detected early. Increased incidence has been observed during the past two decades, including the United States, Australia, Italy, the United Kingdom, and Greece.

In the U.S., the rate increased 75.3% from 1987 to 2002. While changes in American laboratory practices and screening methods along with changes in proportions of multiple pregnancies, race, birth weight, and gender in the population may explain some of the increase, several reports conclude that there are other, unknown factors that account for this temporal trend.

Environmental factors pose one possible cause of these increases. One report examining the potential risk of CH from perchlorate in drinking water found no association. Another found significant links between CH risk and levels of dioxin-like compounds and organo-chloride pesticides detected in the maternal breast milk.

Another potential environmental risk factor is prenatal exposure to radioactive iodine isotopes, which seek out the susceptible fetal thyroid gland. For decades radioactive iodine has been recognized to cause adverse effects (including hypothyroidism) to the thyroid gland. The fetal thyroid, the first glandular structure to appear in the human embryo, begins to concentrate iodine and produce thyroid hormones by the 70th day of gestation. In the mid-1950s, during the period of atmospheric nuclear weapons tests, I-131 produced by fission was first detected in the adult human thyroid. I-131 concentrations were calculated to be about 10 times higher in the human fetal thyroid vs. the human adult or hog thyroid, and maximum elevations in fetal thyroids were detected approximately one month after nuclear explosions. The main path of exposure to short- lived isotopes such as I-131 is via dairy products due to radioactive fallout deposition on forage. 

One report on relatively low doses of I-131 exposures to rat embryos resulted in large decreases in fetal thyroxine and increases in Thyroid Stimulating Hormone (TSH), dependent upon the time of pregnancy that the exposure occurred. A recent analysis discovered levels of whole blood iodine in three infants from Oregon (US) screened at birth exceeded the average for controls by a factor of 10.

A national study conducted by the National Geological Survey examined concentrations of wet depositions of fission-produced isotopes in soil at sites across the US, for several radioisotopes, between March 15 and April 5 2011. Results showed that for I-131, the highest depositions, in becquerels per cubic meter, occurred in north-west Oregon (5100), central California (1610), northern Colorado (833), coastal California (211), and western Washington (60.4). No other station recorded concentrations above 13. Similar results were observed for Cesium-134 and Cesium-137. All the cited locations are on or near the Pacific coast, with the exception of Colorado, in the western US. Thus, the data indicate the greatest concentrations of environmental I-131 in the continental US after Fukushima occurred on the west coast. While the excess is difficult to quantify precisely, for purposes of this report comparisons in airborne gross beta concentrations will be made between the five Pacific and West Coast states (Alaska, California, Hawaii, Oregon, and Washington) and the remainder of the nation. The source of data is the US Environmental Protection Agency’s twice-weekly measurements in nearly 100 US locations, creating a large sample of hundreds of measurements in the weeks after the arrival of Fukushima fallout.

No comments:

Post a Comment

Comment Guidelines: Please be respectful of others at all times. Thanks for reading and thanks for your comments!