Organophosphate triesters (OPEs) are widely used as plasticizers and flame retardants. We investigated the degradation of OPEs in seawater and their effects on the physiology and composition of microbial communities with special focus on their potential influence on the marine phosphorus (P) biogeochemical cycle.

Experiments were performed in July 2014 using surface seawater from the Blanes Bay Microbial Observatory (NW Mediterranean) to which OPEs were added at environmentally relevant concentrations. The concentrations of OPEs in the dissolved-phase generally decreased after 24 hours of incubation at in situ conditions. Thes decreases, measured as the fitted first order reaction constants were significantly different than zero for the trihaloalkyl phosphate tris(2-chloroethyl) phosphate and trialyl phosphate tricresyl phosphate. In general, OPEs triggered an increase of the percentage of actively respiring bacteria, total bacterial activity, and the number of low-nucleic acid bacteria, and a decrease in the percentage of membrane-compromised bacteria. Members of different phylogenetic bacterial groups, mostly Flavobacteria, increased their specific activity indicating that seawater contains bacteria with the potential to degrade OPEs. In seawater limited by labile dissolved organic carbon and phosphorus, alkaline phosphatase activities were seen to significantly decrease with increasing concentrations of OPEs, indicating a relief on P stress, and thus confirming that OPEs can potentially be used as a P source.