THE UPTAKE AND DISTRIBUTION OF (HGCL2)-HG-203 AND (CH3HGCL)-HG-203 IN THE STARFISH ASTERIAS-RUBENS AFTER 24-H EXPOSURE STUDIED BY IMPULSE COUNTING AND WHOLE-BODY AUTORADIOGRAPHY

We have studied the short-term uptake and the distribution of (HgCl2)-Hg-203 and (CH3HgCl)-Hg-203 in the starfish Asterias rubens. Two groups of five starfish were exposed for 24 h to (HgCl2)-Hg-203 and (CH3HgCl)-Hg-203, respectively, at a concentration of 200 ng Hg.l-1 (0.14 muCi.l-1) in artificial seawater (S = 35 part per thousand T = 11-degrees-C). The distribution of inorganic Hg and methyl-Hg were determined by impulse counting and whole body autoradiography. Methylmercury exposure led to an average Hg concentration of 3-times higher than exposure to inorganic Hg (7.40 +/- 2.34 ng Hg.g-1 vs. 2.37 +/- 0.41 ng Hg.g-1), Nearly all the methyl-Hg (94%) and most of the inorganic Hg (77%) were located on the external surface of the starfish. The gonads accumulated 5-times more inorganic Hg than methyl-Hg. Autoradiograms showed the presence of methyl-Hg on specific sites on the exterior body wall and inorganic Hg in the hemal system. The mean Hg concentration ratio between external surfaces and internal organs is 11.7 for MeHg and 2.7 for inorganic Hg. This high ratio for starfish exposed to methyl-Hg is an indication of a slower translocation rate for methyl-Hg. The hemal system appeared to be of primary importance for the distribution of Hg in Asterias rubens and is probably responsible for the higher accumulation of inorganic Hg than methyl-Hg in gonads.