Contamination of terrestrial gastropods, Helix aspersa maxima, with 137Cs, 85Sr, 133Ba and 123mTe by direct, trophic and combined pathways

Madoz-Escande C., Simon O.
Journal of Environmental Radioactivity, Volume 89, Issue 1, 2006, Pages 30-47

137Cs, 85Sr, 133Ba and 123mTe contaminations of terrestrial gastropods, Helix aspersa maxima, by direct deposition, labelled food ingestion or combined (trophic and direct pathways) exposure were carried out under laboratory conditions. The aim of this study was to compare the three contamination pathways: direct, trophic and combined, in terms of individual mortality, radionuclide uptake, depuration and distribution in the tissues. An initial group of 30 snails (2 years old) was exposed to radioactive aerosols during a 20-h period. These aerosols were assumed to be representative of those that would be released during a nuclear accident occurring in a PWR. A second group of 50 snails (same age) was submitted to an ingestion of commercial food contaminated by the same aerosols, twice a week for 21 days (flour at a feeding rate of about 0.2 g). A third group of 40 snails was submitted to a combined exposure: exposure to radioactive aerosols (20 h), followed by ingestion of flour contaminated by the same aerosols, twice a week for 21 days. No significant difference between the three groups and a reference group of 10 snails was observed, neither in growth nor in mortality. Concerning the direct pathway, at the end of direct deposition (about 1 day after the beginning), cesium was the most bioavailable element, distributed rather homogeneously throughout the whole body (13% of the total Cs in all organs excepting the digestive system and 28% in the muscle). Strontium was measured in the shell (about 70%). Barium was found in the muscle (20%) and in the shell (65%). Tellurium was mainly present in the shell (70%) and in the digestive system (20%). After 21 days of depuration, the faeces eliminated 42% of the Te. As for contamination by ingestion, Te mainly accumulated in the digestive system (72% of Te present in the total body), Ba accumulated in the muscle (75%) and Sr in the shell (70%). Concerning contamination by combined pathways, at the end of the 21-day exposure, the 4 radionuclides had the same tendency as direct deposition. However, the effect of the trophic pathway was significant: it causes an 18% increase of Sr in the shell and an 7% increase of Cs in the digestive system in comparison to direct deposition, resulting in a final 86% in the shell and 27% in the digestive system.