TAPES PHILIPPINARUM AS AN ARCHIVE OF HEAVY METAL POLLUTION IN LAGOONS OF THE NORTHERN ADRIATIC COAST, ITALY: A BIVALVE SCLEROCHEMICAL APPROACH

Inquiry into the utility of bivalve sclerochemistry as an archive of heavy metal pollutants within aquatic settings has produced mixed results. Factors beyond the actual concentration of pollutants within the environment, including varying growth rates and other physiological factors of the bivalve, can influence heavy metal concentration within the shell. Here we investigate the utility of the invasive infaunal suspension feeding bivalve Tapes philippinarum as a sclerochemical archive of heavy metal pollution in lagoons of the northern Adriatic Sea, Italy. In May 2014 we collected live and dead/articulated specimens from the Laguna di Venezia (LdV), Sacca di Canarin (SdC), and Sacca di Scardovari (SdS). The LdV has experienced intense pollution due to its long urban history and industrial development, however the SdC and SdS are in close proximity to rural/agricultural settings and are important commercial shellfisheries. Therefore, we hypothesize that the heavy metal concentrations of bivalves will be greater in the LdV than in the SdC or SdS. To date, eight individuals (two from LdV and three from both SdC and SdS) were sectioned along growth for serial analysis of trace element content via LA-ICP-MS resulting in a total of 1,226 spot analyses (40 µm x 80 µm in size) spaced 100 µm apart. When parsed by location, the median concentrations of Ni, Zn, Cu, Cd, and Pb were significantly higher in LdV than in SdC and SdS. This general spatial pattern is consistent with our hypothesis. There are, however, significant differences in median heavy metal concentration among individuals from the same location. Moreover, temporal (ontogenetic) trends of heavy metal concentrations from live-collected individuals from the same location were typically incongruent. These heavy metal concentrations were typically positively correlated with K:Ca, suggesting association with the organic shell matrix. Bivalve sclerochemistry can provide reliable results regarding the spatial distribution of heavy metal pollution when pooling numerous analyses from multiple individuals per location. We cannot yet yield consistent pollution histories for a given location at the temporal scale of the life span of an individual, however this is not to say that we could not resolve pollution history at the scale of successive stratigraphic intervals.