It's a fish story that sounds like science fiction: scientists studying the effects of radiation have discovered that trout exposed to x-rays can pass on the effects to nonirradiated fish. Although experts are skeptical, the researchers contend their study is one of the first to demonstrate the communicability of radiation responses between animals. In addition, the team says the findings underscore the need to investigate whether the phenomenon also can occur in humans.
Considerable previous research in cell cultures has demonstrated that low doses of ionizing radiation results in "bystander" effects, in which nearby, unexposed tissues suffer cell death, mutations, and tumor-inducing growth (ScienceNOW, 7 September 2005). However, few studies have been conducted on live animals. Fish are good candidates for study, because they communicate via chemicals in water. To see if radiated fish release signals to neighbors, a team led by radiation biologists Colin Seymour and Carmel Mothersill of McMaster University in Ontario, Canada, x-rayed pairs of rainbow trout in a water-filled tank for 5 minutes. The total radiation delivered, 0.5 gray (Gy), was high relative to environmental levels (from sources such as naturally occurring radon in rock), but significantly lower than equivalent human doses experienced in CAT-scans or cancer therapy.
The fish were then plunked in another tank with a pair of healthy, untreated trout for 2 hours. In addition, the team placed another pair of nonirradiated fish in the water tank in which the irradiated fish had been swimming. Each experiment was done four times. When the researchers later examined the fish, they found similar radiation effects in all three experimental groups. Cells in five different organs had died and other cells were expressing proteins associated with radiation responses. It's likely that the irradiated fish secreted chemicals--not yet identified--into the water, evoking radiationlike effects in the unexposed groups, the team reports online 27 September in Environmental Science & Technology. The take-home message, says Mothersill, is that bystander effects occur in living organisms, and thus should be taken into account when determining radiation risks in humans and other animals.
Radiation scientist Antone Brooks of Washington State University, Richland, finds the study intriguing. But he cautions that, due to the small sample size used by the team, "it is not possible to see well-defined trends that would suggest the existence of bystander effects." And Mary Helen Barcellos-Hoff, a cell biologist with Lawrence Berkeley National Lab, California, adds that cellular studies have identified specific chemical signals induced by radiation, whereas the trout study has not.
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