Synthetic chemicals are an important part of human society and are used for a variety of purposes ranging from use in materials such as plastic packaging, clothing, and other applications such as use as pesticides and in industry. Generally these chemicals are safe; however, certain types of synthetic chemicals have properties that are damaging to the environment (people included). Specifically, organic (carbon-containing) compounds that are resistant to break down, can move by evaporation from products or applications, accumulate in the food web, and are toxic to wildlife and people are termed “Persistent Organic Pollutants” or “POPs.” Some of the best known POPs include polychlorinated biphenyls (PCBs, mainly used in electrical transformers), DDT, chlordane (pesticide), hexachlorocyclohexanes (HCHs; pesticide) and polybrominated diphenyl ethers (PBDEs, flame retardant). Fortunately, many POPs have been regulated by laws or phased out of production because they were recognized as being persistent (don’t break down) and generally bad for the environment. For instance the Stockholm Convention (http://chm.pops.int/) is a global treaty aimed at eliminating POPs. Despite regulations and phase-outs, levels of POPs in many aquatic food webs are only slowly declining. This is because materials containing POPs or soils containing pesticides act as reservoirs that can re-supply the environment. POP breakdown is also slow in cold regions such as the Arctic and cold areas act as a place where POPs wafting up from warmer regions can condense (like water condensing on a cold beverage).
So what is the status of POPs in Sarasota dolphins in response to POP phase-outs? Our prior work has shown that POPs in Sarasota Bay bottlenose dolphins were present at concentrations that may be toxic to dolphins and that many different types were present including those named above. Are POPs concentrations declining in dolphins or are they more stable like we see in the Arctic? We set out to answer this question by measuring POPs in dolphin blubber that had been collected from Sarasota Bay during 2000-2016 health assessments. We focused our efforts on measuring POP levels in male dolphins as POP levels in female dolphins are greatly changed through offloading of POPs to their calves. We measured concentrations of PCBs, DDT and its degradation products, chlordanes, and PBDEs.
Our data reveal good news from Sarasota dolphins. Concentrations of POPs are declining at about 21% per year, which relative to marine mammals from the Arctic is a steep rate of decline. POP levels in marine mammals from Arctic locations are generally declining at most only 5 to 10% per year. Our results suggest that regulations and phase out systems of POPs appear to be working. In addition, we think that the warmer water of Sarasota Bay enhances the loss of POPs to the atmosphere. Once in the atmosphere, POPs can be moved away from Sarasota Bay and, with fewer POP sources, concentrations in the food web (and dolphins) go down. Declining POPs in the Sarasota Bay dolphin population may begin to free dolphins from their toxic effects, resulting in better survival of dolphin calves and generally improved health. Support for these analyses was provided in part by Dolphin Quest, Inc.
This article appeared on pages 16-17 of the 2017 SDRP Annual Report, Nicks n Notches.