sediment." They were still within food safety limits. In June 2016 Tilman Ruff, co-president of the political advocacy group "International Physicians for the Prevention of Nuclear War", argues that 174,000 people have been unable to return to their homes and ecological diversity has decreased and malformations have been found in trees, birds, and mammals. Although physiological abnormalities have been reported within the vicinity of the accident zone, the scientific community has largely rejected any such findings of genetic or mutagenic damage caused by radiation, instead showing it can be attributed either to experimental error or other toxic effects. Five years after the event, the Department of Agriculture from the University of Tokyo (which holds many experimental agricultural research fields around the affected area) has noted that "the fallout was found at the surface of anything exposed to air at the time of the accident. The main radioactive nuclides are now caesium-137 and caesium-134", but these radioactive compounds have not dispersed much from the point where they landed at the time of the explosion, "which was very difficult to estimate from our understanding of the chemical behavior of cesium". The atmosphere was not affected on a noticeable scale, as the overwhelming majority of the particulates settled either within the water system or soil surrounding the plant. In February 2018, Japan renewed the export of fish caught off Fukushima's nearshore zone. According to prefecture officials, no seafood had been found with radiation levels exceeding Japan safety standards since April 2015. In 2018, Thailand was the first country to receive a shipment of fresh fish from Japan's Fukushima prefecture. A group campaigning to help prevent global warming has demanded the Food and Drug Administration disclose the name of the importer of fish from Fukushima and of the Japanese restaurants in Bangkok serving it. Srisuwan Janya, chairman of the Stop Global Warming Association, said the FDA must protect the rights of consumers by ordering restaurants serving Fukushima fish to make that information available to their customers, so they could decide whether to eat it or not. On February 2022, Japan suspended the sale of black rockfish from Fukushima after it was discovered that a catch was found to be 14 times more radioactive than the legally permitted level. Thyroid screening program The World Health Organization stated that a 2013 thyroid ultrasound screening program was, due to the screening effect, likely to lead to an