![]() On an expedition in June 2011, biologists collected samples of phytoplankton, zooplankton (bottom), and fish, including the tiny hatchetfish (top), to learn if radioisotopes from Fukushima were accumulating in marine life. Marine invertebrates, such as bottom-dwelling starfish and sea urchins, are particularly proficient at absorbing a wide range of ingested radioisotopes, he said, but fortunately, they lose that incorporated radioactivity over time, via excretion. Consumed radioisotopes are assimilated internally through the gut, potentially a far more efficient route than if they are absorbed externally from the environment. But both worms and clams took up much more of the radioisotopes from Pacific sediments, which contain relatively high amounts of silica minerals, than they did from Atlantic sediments, which contain more carbon minerals.įood is another pathway into marine organisms and “may be in some cases the most important factor in uptake,” Fowler said. In one experiment measuring uptake of americium, worms exposed to contaminated sediments took up significantly more of the radioisotope than clams did. Radioisotopes are also transferred to marine organisms from contaminated sediments-once again in ways that display a complex range of factors, Fowler noted. Octopi and crabs took up about half as much plutonium as clams, but about 100 times more than bottom-dwelling fish.Īnother cross-species comparison showed that organisms took up different amounts of radioactivity depending on which particular radioisotopes were out there, he said. Phytoplankton accumulated roughly 10 times as much plutonium as microzooplankton, which took up 100 times more than clams. In an experiment in the early 1980s, Fowler demonstrated vast differences in how much plutonium was absorbed from seawater by marine life across a spectrum of taxonomic groups. “Polonium is responsible for the majority of the radiation dose that fish and other marine organisms receive,” he said. Potassium-40 is the most abundant radioisotope in the ocean, but polonium-210 accumulates more readily in marine organisms. Polonium-210 and potassium-40 are naturally occurring radioisotopes in the ocean, for example. In all this, Fowler said, it’s important to remember the omnipresence of natural background radiation. How much radioactivity gets into marine life depends on a host of factors: How long the organisms are exposed to radioactivity is certainly important, but so too are the sizes and species of the organisms, the radioisotopes involved, the temperature and salinity of the water, how much oxygen is in it, and many other factors such as the life stage of the organisms. These particles accumulate in sediments, and some radioisotopes contained within them may be remobilized back into the overlying waters through microbial and chemical processes. ![]() As the phytoplankton are eaten by larger zooplankton, small fish, and larger animals up the food chain, some of the contaminants end up in fecal pellets or other detrital particles that settle to the seafloor. These organisms take up radioactive contaminants from the seawater that surrounds them. The food chain starts with marine phytoplankton-microscopic plants that account for as much photosynthesis as plants on land. How did that pulse of cesium and other radioisotopes make its way through the marine food chain? Scott Fowler, who helped pioneer marine radioecology for more than 30 years at the International Atomic Energy Agency’s Marine Environment Laboratories, offered a primer on the subject at the Fukushima and the Ocean Conference in Tokyo in November 2012. The Fukushima nuclear disaster delivered an unprecedented amount of radioactivity into the sea over a relatively brief time. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |