Summary of assessment of GESAMP Working Group 37

This presentation is based on the summary of the GESAMP report to UNEP on mercury in the aquatic environment. The summary is divided into three main sections: Sources and releases, aquatic and oceanic transport and assessment of monitoring and evaluation. Sources can be natural or anthropogenic in origin with both diffuse and point sources being considered. While point sources are the most direct entry into an aquatic system, atmospheric deposition is the dominant input component to the world oceans. Consequently, reduction of mercury emissions must be the dominant mechanism of control. Wet deposition is a primary mechanism for transporting mercury from the atmosphere to surface water and land. Once in aquatic systems, it can exist in dissolved or particulate forms and can undergo a number of chemical transformations. Contaminated sediments at the bottom of surface waters serves as a mercury reservoir with sediment-bound mercury, recycling back into the aquatic ecosystem for decades or longer. Mercury has a long retention time in soils, so mercury that has accumulated in soils may continue to be released to surface waters and other media for long periods. Methylmercury (CH3Hg+)is the most common form of organic mercury in the environment and is more toxic than elemental or inorganic mercury with the potential for bioconcentration and bioaccumulation via the aquatic food web. This places people, all over the world, who consume predatory fish (or where fish is a dietary staple) at risk. The methylation of mercury occurs by biotic and abiotic processes, and transformation processes are influenced by several environmental factors such as pH, temperature, sulphate deposition, and availability of biodegradable organic carbon. Currently there are 2 main ways to evaluate concentrations of mercury in the environment based on principles of modelling or measuring techniques. Modelling programs have been studied to better understand the behaviour of substances in environmental media and used to estimate for mercury and its compounds in various environmental compartments. The advantages and disadvantages of modelling versus measuring techniques will be presented in full.