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In order to assess the effect of alternating electromagnetic and direct magnetic field on adult Helix aspersa O. F. Müller and their eggs, adults and eggs of H. aspersa maxima Taylor and H. aspersa aspersa O. F. Müller were exposed to such fields with different parameters, and the following life cycle traits were observed: condition of hibernating adults, their survival rate during hibernation and reproduction, egg mass, hatching success, growth rate of hatchlings and body mass of next generation adults. Adults were exposed to sinusoidal, alternating electromagnetic fields of 50 Hz, 100 Hz and 200 μT, and magnetic induction of 50 Hz, as well as a field of 175 μT and 10–1000 Hz (repetition period 80 minutes). Egg batches were exposed to direct magnetic fields of magnetic induction 5 μT and 10 μT and alternating electromagnetic fields of analogous induction and frequency of 50 Hz. The effects varied depending on the parameters of the fields, subspecies and life cycle stage. Adult H. aspersa maxima was more sensitive to the changes in characteristics of electromagnetic field than H. aspersa aspersa, but the two subspecies showed a similar reaction to exposing their eggs to direct or alternating magnetic field. Probably direct field had a greater selection effect compared to alternating field, removing weaker genotypes at embryonic stage; this resulted in a greater mean body mass of the next generation adults. The results are preliminary; further studies, with further modifications of parameters of the fields applied are necessary.
The interaction of lead and calcium assimilation was examined in the soft tissues, shell and faeces of the soft tissues, shell and faeces of the garden snail an induced calcium stress, shell wounding. This is known to mobilise Ca both from the shell and soft tissues, conditions which are likely to affect Pb assimilation by each component Following wounding, snails were fed an artificial diet for 7 days with some combination of Pb and/or Ca and Mg in a 22 factorial experiment Dietary Pb raised the concentration of this metal in all tissue components, though the scale of the increase was the same in both wounded and unwoun- ded snails. The smallest increase was in the shell. Ca and Mg levels in the hepatopancreas remain unchanged by the dietary levels of any treatment, but were raised in the rest of the soft tissues. Significantly, the high Pb diet is almost equally effective as wounding in lowering the Ca in this component. Injuring the shell had little effect on the uptake of Pb by the snails.
Pb uptake by three populations of the snail Helix aspersa was measured in a series of experiments supplying PbS04 in an agar diet. Uptake rates in snails from a site grossly polluted with Pb were lower than in the two other populations and were unafected by the initial body burdens of Pb. Populations of snails from a Pb-free site showed much greater variability in tissue Pb burdens and faster rates of accumulation than populations from the polluted site. Snails from a site with Pb concentrations between the other two sites showed intermediate rates of uptake. It is suggested that snails from the highly contaminated site have adapted to high environmental levels of Pb and that this adaptation is genetically based.
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