My last week at the University of Liege has arrived, and I’m working hard to ensure that all the PHATS team’s labwork is complete before I leave to return home. All of our samples are now ready for analysis that will let us detect PCB and PBDE levels in our Scottish grey seals. PCBs and PBDEs are two types of the many persistent organic pollutants (POPs) that are present in our environment. I am currently working on preparing our samples for another type of analysis that will enable us to detect a third kind, OCPs. As POPs in our environment, and PCBs in particular, are still currently in the news after the recent revelation of just how highly contaminated with PCBs some marine mammals are becoming, I thought I’d spend this blog introducing the three types of POP I work on and why they are so problematic.
PCBs, or polychlorinated biphenyls, are pollutants that are made up of two linked rings of carbon atoms with a varying number of hydrogen and chlorine atoms bound to the rings at different positions. There are many possible combinations of the number and locations of the hydrogen and chlorine atoms binding to the rings, and these give rise to the large variety of PCBs (called congeners) that exist. Approximately 130 different types of PCB are found in commercial products, and they can be divided into two groups (dioxin-like and non-dioxin-like) based on their structure and toxicity. PCB production was banned in the USA in 1979 and by the Stockholm convention (signed by over 150 countries worldwide) in 2001, however they persist in our environment due to their slow degradation rates. One of the main reasons PCBs were previously manufactured and used in industry was their inert properties; only incineration at high temperatures can safely destroy them. Previous uses of PCBs include in coolants and lubricating oils, paints and electric wire coatings.
PBDEs, or Polybrominated diphenyl ethers, are also made up of two carbon rings, but they have bromine bound to the rings rather than chlorine. The fewer the bromine atoms per molecule of PBDE, the more dangerous they are considered to be as congeners with between 1-5 bromine atoms bioaccumulate more effectively in living organisms. PBDEs are still being manufactured and widely used in many man-made products, the Stockholme convention which banned PCBs only restricted the production of some PBDEs. Some states in the USA have begun prohibiting their manufacture and use in the last decade however. PBDEs are flame retardant and are therefore commonly incorporated into electronics, plastics, fabrics and other building materials.
OCPs, or organochlorine pesticides, contain carbon, hydrogen and at least one bound chlorine atom but do not contain carbon ring structures like PCBs and PBDEs. There are many different types of OCP, however arguably the most well known is DDT (Dichlorodiphenyltrichloroethane) which was heavily used as a pesticide across the world to kill insects for both agricultural and disease control purposes. The famous book ‘Silent Spring’, written by Rachel Carson in the 1960s, is all about OCPs and the negative impact overuse of pesticides has on the environment. The production and use of some OCPs like DDT and heptachlor has been strictly limited by the Stockholme convention. Due to their efficiency at killing insects, their use is still permitted in some circumstances, such as the use of DDT to control mosquitoes that carry diseases like malaria.
POPs have been connected to a wide range of negative health impacts in both people and wildlife, and chronic exposure to any type of POP will cause problems for any organism. All POPs are carcinogenic (cancer causing) and are potent endocrine disruptors, interfering with growth and development, immune function and reproductive systems. There is growing evidence that POPs impact on obesity, leading them to be labelled as ‘obesogens’. The PHATS project I am part of is hoping to uncover some of the underlying physiological and genetic mechanisms that influence fat tissue function and determine how POPs can interfere with these processes. By studying a marine mammal species which has lots of fat and lots of bioaccumulated POPs, we can gain a better understanding of how these chemicals have such far reaching and devastating impacts on our health and the environment.