Irradiation Can Be an Alternative to Fumigation
By Harvey Black
USDA Agricultural Research Service scientist Peter Follett has been working for nearly 20 years to develop and expand the use of ionizing radiation to control insects that infest a range of agricultural commodities so that Hawaii can safely send these products to the U.S. mainland and export them to foreign countries.
Hawaii currently irradiates a number of crops it exports, including papaya, mangoes, bananas, dragon fruit, and longan, a small circular fruit grown by the tree of the same name.
Most recently, Follett and his colleagues have worked to develop irradiation protocols to use on insects that infest Hawaiian commodities such as coffee and ornamental flowers. They have also been working to protect others, such as table grapes and a variety of berries grown in California.
“[Irradiation] is the most prominent technology that we’re using to export fruit to the U.S. [mainland] from Hawaii,” said Follett, who works at the U.S. Pacific Basin Agricultural Research Center in Hilo, Hawaii.
Since starting work for the ARS, Follett has helped develop irradiation techniques to control a range of agricultural pests, including the mango seed weevil, the oriental fruit fly, the Mediterranean fruit fly, and the melon fly.
The first irradiation facility in Hawaii opened in 2000. The ionizing radiation comes from electron beams, gamma radiation, or X-rays.
In an article in International Innovation, Follett notes that in the past several years, India, Mexico, Pakistan, South Africa, Thailand, and Vietnam, have reached agreements with the U.S. on using irradiation on fruits and vegetables and are exporting millions of pounds of these commodities.
Developing an irradiation protocol involves a several-step process, Follett explained. Initially, researchers must develop a system to raise large numbers of an insect pest. Next comes the development of a range of doses to determine how much is needed to either sterilize the pest or prevent it from becoming an adult in the commodity to be irradiated. Following that are large-scale tests at the radiation dose they predict to be effective. Finally, the USDA’s Animal and Plant Health Inspection Service reviews the data and establishes a protocol for the use of radiation.
The countries that would import the irradiated commodities also have to approve the protocol.
Follett and his colleagues have found the appropriate dose of radiation to control the western flower thrips and the coffee berry borer in Hawaii, and to control the European grapevine moth and the spotted wing drosophila, both of which are pests in California.
“In the case of western flower thrips, coffee berry borer, and spotted wing drosophila, we are trying to sterilize adults that are potentially reproducing,” Follett said. “In the case of the European grape vine moth, we are trying to prevent emergence of adults, and if some adults do emerge we’re trying to make sure they’re sterile.”
The use of radiation on such post-harvest commodities, which is a form of phytosanitation, is an alternative to using methyl bromide, a toxic fumigant that damages the Earth’s protective ozone layer. While the Montreal Protocol required its use to be stopped by 2005, the U.S. Environmental Protection Agency permits its use on a “critical exemption basis.”
According to the EPA, when used as a fumigant, methyl bromide gas is injected into a tarpaulin or container containing the commodity to be fumigated and “a high proportion of methyl bromide used for a typical commodity treatment eventually enters the atmosphere.”
More environmentally benign than methyl bromide, irradiation has been endorsed by a range of medical organizations as an effective and safe tool to keep food safe. For instance the U.S. Centers for Disease Control and Prevention make it quite clear that irradiation of foods poses no health threat.
According to the CDC website, “The safety of irradiated foods has been studied by feeding them to animals and to people. These extensive studies include animal feeding studies lasting for several generations in several different species, including mice, rats, and dogs. There is no evidence of adverse health effects in these well-controlled trials. In addition, NASA astronauts eat foods that have been irradiated to the point of sterilization (substantially higher levels of treatment than that approved for general use) when they fly in space.”
Furthermore, the World Health Organization notes that irradiated foods do not become radioactive.
Follett and his colleagues are also working to make the irradiation process simpler. Currently, food irradiation is done in large facilities. With a $360,000 grant from the USDA Foreign Agricultural Service, Follett is working to build a “cabinet-style food irradiator.” He says that such a device would make irradiation more convenient and easier to do.
“Smaller packing houses and growers might be able to purchase these at a much lower cost [than sending the product to irradiators] and treat their own fruits for export,” he said.
Harvey Black is a freelance science writer. A long-time resident of Madison, Wisconsin, he has written for numerous publications including Environmental Health Perspectives, Scientific American Mind, New Scientist, The Scientist, and the Milwaukee Journal Sentinel.