ABSTRACT
Among the most intensely studied contaminants in estuarine and marine environments are heavy metals, a group of elements with atomic weights ranging from 63.546 to 200.590 and characterized by similar electronic distribution in the external shell (e.g., copper, zinc, cadmium, zinc). Heavy metals enter the sea via several major routes, most notably riverine influx, atmospheric deposition, and anthropogenic activities. The coastal supply of heavy metals results mainly from atmospheric and riverine delivery systems. Both physical and geochemical processes control the distribution and transport of heavy metals in estuaries. Heavy metals clearly undergo varying degrees of recycling in estuaries. Estuarine and marine organisms tend to accumulate heavy metals from the environment, with both metal speciation and bioavailability being important in this process. Natural inputs of mercury to aquatic systems originate from the weathering of mercury-bearing rocks and ores (e.g., cinnabar), the fallout of atmospheric gases from volcanoes and geothermal vents, and the emission of deep-sea hydrothermal vents.
