Mercury in the aquatic environment: A review of factors affecting methylation

Mercury is one of the most hazardous contaminants that may be present in th e aquatic environment, but its ecological and toxicological effects are str ongly dependent on the chemical species present. Species distribution and t ransformation processes in natural aquatic systems are controlled by variou s physical, chemical, and biological factors. Depending on the prevailing e nvironmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotox in that is readily accumulated by aquatic biota. Despite a considerable amo unt of literature on the subject, the behavior of mercury and many of the t ransformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current s tate of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its t ransformation into highly toxic methylated forms.