Die opname, verspreiding en invloed van koper by Xenopus laevis (Daudin)

Abstract

(1) Adult female Xenopus laevis were subjected to copper concentrations ranging from 25 to 1 250 µ,g mf1 for a period of 96 hours to ascertain their sensitivity towards the heavy metal. A more confined range was selected after this (25 , 62.5, 125, 187.5 and 250 µ,g mf 1 ) and the dose of 62.5 µ,g mf 1 was established as the 96 hours LD50 value. (2) Due to the influence of adsorption of copper on the aquarium walls and its precipitation due to pH-levels of the exposure media, the copper concentration decreased from 62.5 µ,g mf 1 to 14.2 ± 2.55 µ,g ml-1 in aquaria without specimens after 96 hours. When animals were placed in exposure media, the copper concentration decreased from 62.5 µ,g mf 1 to a lower value of 11.8 ± 0.45 µ,g m1- 1 after 96 hours, illustrating the degree to which exposed animals accumulated the heavy metal. (3) To determine the accumulation of copper inXenopus, groups of80 animals were exposed to either clean water or 62.5 µ,g mf1 copper for 96 hours. Every 24 hours, 10 animals from both a control and an exposure medium were removed and the following tissues were sampled: blood, skin, alimentary canal (from oesophagus up to rectum), lungs, kidneys and liver. The copper concentration in each tissue was measured by atomic absorption spectrophotometry after nitric acid digestion. ( 4) Results indicate that the mean copper concentration was significantly highest in the alimentary canal and that the following tissues contained copper in order of decreasing concentrations: liver > skin > kidneys > lungs > blood. (5) To determine whether the accumulated copper can be successfully excreted, animals were exposed to an initial copper concentration of 62.5 µ,g mf1 for 96 hours. Thereafter 80 animals were removed and transferred to copper-free water for 96 hours. Every 24 hours 10 animals from both a control and an exposure medium were removed and the same tissues as above were sampled for copper. (6) Results indicate that liberation of copper occurred solely from the skin during the 96 hour excretion period. Copper concentrations varied considerably in the other tissues, but exhibited high levels of primarily adsorbed copper which were not released during the 96 hour excretion experiment. (7) Copper-induced histological damage to the various tissues and histochemical localisation of copper were studied in both exposed and control specimens. Results indicate that the skin of exposed animals was damaged to a great extent. Scanning electron microscopy revealed the extent to which copper afflicted the epidermis of exposed animals.