Mercury in surface sediments and benthic organisms from Guaymas Bay,east coast of the Gulf of California

In order to know the concentration of mercury in surface sediments, macroalgae and clams from Guaymas Bay, Mexico, 20 surface sediment samples and several individuals of Codium amplivesciculatum (3), Enteromorpha clathrata (4), Gracilaria subsecundata (2), Ulva lactuca (2), Chione subrugosa (80) and Crassostrea gigas (40) were collected and their Hg concentration was measured by a cold vapor Hg analyzer, after acid digestion. In addition, granulometric analysis and quantification of total organic carbon, aluminum, iron and manganese contents in sediments were performed. A Pearsons correlation matrix was determined and, the enrichment factor, the geoaccumulation index and the biota-sediment accumulation factor were calculated. Mercury concentrations in sediments ranged from 0.3 to 2.3 μg g⁻¹, with the central and northern portions showing the highest values. Macroalgae had a content of Hg that oscillated from 0.058 to 0.134 μg g⁻¹, while the average concentrations of this metal for clams and oysters were 0.063 and 0.230 μg g⁻¹, respectively. A clear effect of Guaymas City and the anthropogenic activities carried out around the Guaymas Bay has been observed and the enrichment factor and the geochemical index suggest that sediments from this coastal ecosystem are moderately to strongly contaminated with Hg. However, according to the figure of the maximum human consumption of Hg per week recommended by the World Health Organization, people can ingest clams without risk to their health.