Abstract
There is an increasing concern on effects of radiation and/or radionuclides on non-human biota. In order to elucidate the radiation effects on the non-human biota and the environment, it is essential to develop a new method to assess and estimate the radiation dose. However, the intake and metabolism of radionuclides in the body of non-human biota is little known. In this study, we describe a new method to predict the endodermal transfer (percutaneous uptake) ratios of radionuclides with modification of filter paper tests on the Acute Toxicity Tests according to OECD/NEA.
To investigate the percutaneous uptake of three radionuclides, 109Cd, 134Cs and 60Co in earthworms (Eisenia fetida, hereafter earthworm), they were exposed to the radionuclide solution soaked in filter paper.Filter paper exposure used 50 mL plastic vials lined with Advantec No.1 filter paper contaminated with 1 mL solutions of 109Cd or mixture of 134Cs and 60Co for individual worm exposure.Each vial was kept horizontal at 20 oC under darkness for 3 days, and the radioactivities in the worms were measured every day using a gamma spectrometer with a high purity germanium detector. Prior to the measurement, individual earthworm was washed and blot-drying to remove the radionuclides on the surface of the body.
Percutaneous uptake ratios (the activities in an earthworm to the activities added to a vial) of every radionuclide were increased with time; that of 134Cs was the greatest, 10%, compared with those of 109Cd and 60Co, which were approximately 5%. The mode of uptake ratios with time was different between 134Cs and the others; the uptake mode of the former had approached almost plateau at the end of the tests, and those of the latter were linear. The radioactivities in the water and paper used for removing the radionuclides from the surface of earthworms' body were less than 10% of those in earthworms.
In general, we concluded that this new method presented here is a useful tool to estimate the uptake of radionuclides in earthworm easily. The method showed that 134Cs was absorbed into earthworms rapidly compared with 109Cd and 60Co.
