The overall goal of MERCYMS is to fill the gaps firstly specificated and develop a Practical Working Tool (PWT) for a wide spectrum of users (i.e., policy makers, environmental planners) that would allow to assess for different environmental conditions and socio-economic scenarios, the relationship between the atmospheric input of mercury and its compounds to the Mediterranean Sea and the formation/production of the most toxic forms of mercury (i.e., MMHg, DMHg) in the marine system which have a significant impact on human health and the environment.