Mercury concentrations in sediment profiles of a degraded tropical coastalenvironment

The present and past degrees of contamination by mercury were evaluated in the Guanabara Bay by the study of five sediment cores. The cores were sampl ed from the deltaic mouth of the Sao Joao de Meriti River (cores SJ1, SJ2, SJ3, and SJ4), adjacent to a large mangrove stand and in a mangrove stand i n Guapimirim (opposite side of the bay). The study area receives most of th e domestic and industrial wastes from the metropolitan region of Rio de Jan eiro city and, inconsequence it becomes increasingly degraded. Among the so urces of pollutants, mercury-spilling industries are inventoried in the Sao Joao de Meriti River basin. Total mercury concentrations were measured in the sediments by cold vapour atomic absorption spectrometry. The fraction s maller than 63 mu m, organic carbon and total sulphur concentrations were a lso measured. The results show that concentrations of mercury can reach hig h values (up to 37 mu g g(-1) at a depth of 34 cm in the core SJ4). The bas e of core SJ1 shows mercury concentrations that probably represent backgrou nd values, as established elsewhere for the Guanabara Bay (51 ng g(-1) at t he depth of 32 cm). Among the studied cores, only core SJ1 seems to reach b ackground levels.