Epidermal uptake of Pb, Cd, and Zn in tubificid worms

The epidermal uptake of Pb, Cd, and the essential element Zn by tubificid worms was investigated. The animals were starved and contaminated via the water column at 4°C and 25°C. Atomic absorption spectroscopy (AAS), energy-dispersive X-ray microanalysis (EDX), laser induced mass analysis (LAMMA), electron microscopy, and the sulfide-silver method at the electron microscopical level were used. The sulfidesilver method revealed many reaction products indicating heavy metals in membrane-limited lysosomal structures in epidermal cells of contaminated Limnodrilus udekemianus. In these lysosomes, which were particularly abundant in the epidermis of the hind end, Pb, Cd, and Zn were detected by LAMMA and EDX analysis. Beside this distinct occurrence of the three elements a uniform pattern of reaction products was found in epidermal cells after contamination with Cd and Zn, but not after treatment with Pb. As shown by atomic absorption spectroscopy, Cd was the most enriched element at 25°C, followed by Pb and Zn. Simultaneous application of Zn reduced the uptake of Cd, whereas the uptake of Pb was increased. At 4° C uptake of Pb and Cd was slower than at 25° C, while Zn uptake was blocked completely. This shows that heavy metal uptake can be strongly dependent on environmental conditions, which has to be taken into account if animals are used as monitor organisms for heavy metal pollution in the environment.