Calcium-lead interactions involving earthworms. Part 2: the effect of accumulated lead on endogenous calcium in Lumbricus rubellus.

The calcium and lead burdens of tissue fractions of Lumbricus rubellus were quantified in 'native' animals from acidic and calcareous disused lead mines, and from control ('naive') animals exposed to lead-polluted soils under laboratory conditions. Most of the body burden of lead was accumulated within the posterior alimentary canal, and significant positive correlations were generally found between the calcium and lead burdens in this tissue fraction, which were evident in both the naturally and laboratory lead-exposed animals. The calcium:lead correlation is probably due to a proliferation of the calcium-rich, lead-sequestering chloragosome granules, and may thus be regarded as a specific tissue response to cellular lead incursion. No calcium-lead relationship was recorded in the rest (largely composed of the body wall) fraction of earthworms inhabiting the lead-polluted sites. However, a concomitant increase in calcium and lead in this tissue fraction of the laboratory lead-exposed control animals was noted. It is concluded that in naturally lead-exposed earthworms, the cells of this tissue fraction may be relatively resistant to the toxic effects of the metal. By contrast, it is apparent that a non-specific cytotoxic response by the cells of the rest of 'naive' animals occurs, as demonstrated by the concurrent increase in its calcium and lead burdens. These results suggest that a tolerance mechanism to lead, perhaps with a genetic basis, may exist in earthworms naturally exposed to lead.