Content, absorption quantities and intracellular storage sites of heavy metals in Diplopoda (Arthropoda)

Abstract

By means of atomic absorption spectrophotometry, concentrations of more than 2500 mg kg−1 Pb, 150 mg kg−1 Zn, and 320 mg kg−1 Cd could be detected in the intestine tissues of diplopods from a lead and silver smelter's spoil bank. While only small portions of the ingested lead and cadmium are absorbed in the midgut of these diplopods, the zinc uptake into the midgut epithelium reaches 33.8–37.5% of the zinc content in the food pulp when the animals were contaminated acutely. However, after long-term contamination with zinc, absorption and excretion of this metal balanced one another. Absorbed lead and cadmium are predominantly stored in the midgut cells of the diplopods; unspecific precipitation of heavy metal showed the spherites of the resorptive epithelial cells to be the main accumulation sites. Zinc is for the most part localized in or near the cuticle; electron energy loss spectroscopy and ESI electron spectroscopic imaging, however, showed this metal to be present also in the spherites of the midgut's resorption cells. These spherites are assigned to belong to the ‘type A granule’ group since (i) they are concentrically structured, (ii) they are shown to contain great amounts of calcium and (iii) copper, a class B metal, could not be detected in these deposits.