Neptunium-237 in the marine environment determination in animal and plant species in the English Channel: Biological indicators and trophic relationships

We have studied the uptake of²³⁷Np in marine plants and animals belonging to several phyla, and collected samples from the end of January 1986 to March 1986, in a sampling station situated near the outlet of the irradiated fuel reprocessing plant at La Hague.We determined the²³⁷Np by neutron activation analysis. This method is very sensitive, with a limit of detection of 5×10^–10 mg, 1.3×10^–2 mBq. The method consists of the following steps:Reduction of the neptunium to the tetravalent state by treatment with a mixture of hydrazine sulfate and ferrous iron-chromatographic separations on Dowex 1×10 resin in a nitric medium, then in a hydrochloric medium-neutron irradiation in a nuclear reactor-purification of the neptunium by chromatography on Dowex 1×10 resin in a nitric then hydrochloric medium-measurement of the isotope²³⁸Np by gamma ray spectrometry using a Ge(Li) detector. The species were collected at Goury, at the northwest extremity of the Cotentin Peninsula, 5 km from the outlet of the reprocessing plant at La Hague. The levels of²³⁷Np were as follows: red algaeCorallina officinalis 64 mBq kg^–1 wet weight; andChondrus crispus 18 mBq kg^–1 wet weight; the spongeHalichondria panicea 14 mBq kg^–1 wet weight; the ascidianDendrodoa grossularia 12 mBq kg^–1 wet weight. The bivaive molluscsPatella vulgata andGibbula umbilicalis (the flesh ofP. vulgata andG. umbilicalis: 4 and 7 mBq kg^–1 wet weight respectively) also prove to be interesting biological indicatorsThe transfer modes of²³⁷Np to the various species as a function of their trophic levels are discussed as well as the distribution among the organs in the species consumed and the radiological impact of human consumption.