A first insight of Hg occurrence in the hellenic volcanic arc

Mercury is a highly toxic element with both natural and anthropogenic sources to the marine environment, with implications to ecosystems and human health. It is recognized as a priority pollutant by the European Environmental Legislation and the United Nations Environmental Program (UNEP). The complex geodynamic and geological setting of the Hellenic Volcanic Arc (HVA) in Greece, reflects in a great variety of geochemical compositions for many thermal fluid manifestations and leads to the necessity of studying them separately. The present paper is a preliminary presentation of Hg levels in aquatic samples from Methana peninsula, Kos and Nisyros islands and Yali islet. These study areas are affected by active fault zones which characterized as pathways of elevated heat flow. Samples were collected along the coastline, both from thermal springs and swallow-waters hydrothermal vents and analyzed for Total mercury (THg), trace metals (TM) nutrients, total alkalinity (At), Dissolved Oxygen (DO) and physicochemical parameters where measured in situ. The concentrations of THg were quite variable, ranging from 3.48 to 278.53 pM (mean 32.56 pM), while in Kos spotted the highest (278.53 pM) with no values exceeding the limit set by the WFD (70 ng /l or 349.02 pM). It appears to have a strong positive correlation with nutrients, DO, while strong negative one with pH and At. In the area of Nisyros – Yali the measured THg falls in between the other sites , while in Methana is the lowest levels with strong positive correlation with salinity, conductivity and pH and negative with DO and temperature. Strong positive correlation of THg was with Li, Al, Mn, Fe, As, Sr, Cd in every sample area. We hypothesize that underwater hydrothermal activity may constitute a considerable Hg source to the oceans, as fluids from thermal waters are often brackish to saline due to marine intrusion into the coastal aquifer. As a result, more research is required in these areas in order to determine the amount of Hg contribution to the oceans by the type of volcanism and tectonic activity, as well as the positive correlations between Hg and TM such as As, Cd, Mn and Fe.