The UK Environment Agency has recommended chronic irradiation studies using the earthworm Eisenia fetida ( 5). Based on their radioecological properties and their important role in the soil ecosystem, earthworms have been identified by the ICRP ( 4) as one of the reference animals and plants (RAPs) to be used in environmental radiation protection. Earthworms may receive increased exposure because of the passage of soil through their alimentary tracts, and they also lack the chitinous exoskeleton of some soil invertebrate species, which may reduce exposure from external radiation ( 1). A number of studies of the movement of radionuclides through invertebrate food chains have demonstrated that detrivorous species have higher concentrations of radionuclides (cesium, plutonium, americium) than herbivore and predatory species. In most contamination situations, the majority of the radionuclide inventory in terrestrial ecosystems is found within soil thus soil invertebrates can receive significant external and internal doses. Reproduction is considered to be one of the most sensitive radiation-associated end points ( 3), and it not only determines the fate of the single organism but also may influence the population dynamics and the balance of higher ecological units. However, there are still considerable gaps in knowledge regarding the biological effects of chronic irradiation in wildlife, particularly for end points related to reproduction ( 1, 2). In recent years the ecological impact of ionizing radiation has emerged as an important research field. Traditionally, radiological protection has focused on humans. The lowest dose rates at which an effect was observed were 4 mGy/h in F 0 and 11 mGy/h in F 1.
fetida, but extensive exposure periods (13 weeks) were needed for these effects to be expressed. In conclusion, chronic irradiation reduced the reproduction capacity of E. However, and in contrast to the results observed for F 0, hatchability increased with time, suggesting a possible acclimatization or adaptation of the F 1 individuals. The number of hatchlings (F 2) per cocoon and the total number of F 2 individuals produced was also reduced. For adult F 1, the hatchability of cocoons at 11 mGy/h was reduced to 45–69% during the 13-week exposure period. This number was also reduced at 4 mGy/h, but the effect was of borderline significance. Correspondingly, at these dose rates, the total number of F 1 hatchlings per adult F 0 was significantly lower than in the control. In addition, the number of hatchlings per hatched cocoon was reduced at 11 and 43 mGy/h. At 11 mGy/h the cocoon hatchability was reduced to 25% at 9–13 weeks. For F 0, hatchability of cocoons produced during the first 4 weeks was reduced to 60% at 43 mGy/h (98% in controls), and none of the cocoons produced at 5–13 weeks hatched. There was no radiation-induced effect on the cocoon production rate in either F 0 or F 1. F 1 adults were exposed for a further 13 weeks to determine their reproduction capacity. Survival, growth and sexual maturation of F 1 hatchlings were observed for 11 weeks. Adult F 0 reproduction capacity (i.e., number of cocoons produced, hatchability and number of F 1 hatchlings) in controls and at five dose rates (0.18, 1.7, 4, 11 and 43 mGy/h) was measured over a 13-week exposure period.
168, 515–526 (2007).Įisenia fetida were exposed continuously to 60Co γ radiation during two generations (F 0 and F 1). Effects of Chronic Gamma Irradiation on Reproduction in the Earthworm Eisenia fetida (Oligochaeta).
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