A new experimental scheme for the definition of the natural formation pathways of PBDEs

Our research group has recently investigated POP contamination in the Nador Lagoon (N-E Morocco). Such studies have highlighted a peculiar situation: measurable total concentrations of Polychlorinated biphenyls (PCBs) and Polybrominated diphenyls ethers (PBDEs) were found at depths corresponding to times when these chemicals were not yet artificially produced [1,2]. Post-depositional reworking processes were suggested in order to explain the presence of PCBs shortly before the 1930s [1], but the case of PBDEs was considerably more puzzling: the latter compounds were detected at depths corresponding to the early 1950s at the maximum value measured in the entire sedimentary record [2]. Physical mixing and/or bioturbation processes might have contributed to setting off vertical movements along the core, but it is unlikely that they alone could have produced the observed concentration peak at depth. An additional unforeseen process might therefore have been at work. Two of the most abundant naturally occurring structural analogues of PBDEs (i.e. 6MeO-BDE-47 and 6OH-BDE-47) are very similar to BDE-47 (the most abundant congeners detected in our studied sediments). Therefore, we hypothesized that reducing conditions in buried sediments might have favoured demethylation and dehydroxylation of these compounds to BDE-47. Following bromination processes might then have produced the other observed congeners. The formation of PBDEs from naturally synthesized polybrominated compounds in sediments is a fascinating hypothesis and, if verified, could pave the way to studies aimed at the definition of sources and origin of PBDEs. In this presentation we propose a rationale for a new experimental procedure aimed at studying this formation pathway and at verifying its presence in reducing sediments at laboratory scale. [1] S. Giuliani et al., Science of the Total Environment 526 (2015) 346-57. [2] R. Piazza et al., Marine Pollution Bulletin (2016) DOI: 10.1016/j.marpolbul.2016.05.007.