Marine EnvironmentalResearch 6 (1982)69-82 CHEMICAL LEACHING AND SPECIFIC SURFACE AREA MEASUREMENTS OF MARINE SEDIMENTS IN THE EVALUATION OF MERCURY CONTAMINATION NEAR CINNABAR DEPOSITS F. BALDI & R. BARGAGLI University oJSiena, Via delle Cerchia No. 3, 53100 Siena, Italy (Received: 6 May, 1981) ABSTRACT This paper investigates mercury contamination in recent marine sediment ol the Tyrrhenian continental shelf near the mouths of three rivers draining an area with cinnabar deposits ( M. Amiata, Italy). By means of chemical leaching, two fractions of the total mercury were distinguished: a 'non-leachable' fraction, consisting o.! mercuo' held in relatively stab/e forms and a 'leachable'fraction, composed of/brms that are more weakly bound to the sediments. The two Hgj?actions are correlated to the organic matter content, the distribution oj which is strictly dependent on the sediment surjace area. In order to eliminate the effects oJ grain size variations among the samples, the Hg concentrations were normalized to the unit of suJface area (ng/m2). Following this procedure, the'non-leachable' Hg wasjound to be concentrated mostly in a belt along the coast, while the "leachable' Hg j}'action was shown to accumulate largeO' in the zones with high depositional dynamics near the mouths of the rivers. Hypotheses to account for the discrepancy between the low concentrations oj "leachable' Hg in the sediment oJ the outer continental shelf and the high concentrations in the fauna of the same area, reported in previous papers, are presented. INTRODUCTION The question of mercury contamination deriving from the weathering of mineral deposits and, in certain areas, from the inevitable losses during its extraction and 69 Marine Environ. Res. 0141 - l 136/82/0006-0069/$02-75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain