PCB Bioaccumulation and Cetaceans
What are PCBs?
PCB stands for Polychlorinated Biphenyls, and represents a grouping of man-made chemicals that consist of carbon, hydrogen, and chlorine. PCBs were first produced in the late 1920’s / early 1930’s, and were continued to be used in products until its ban in 1979 (Toxic Substances Control Act) due to the toxicity of PCBs and its negative impacts on biological organisms.
There are a range of PCBs, with varying consistencies (from a thin liquid to a thick wax) as well as varying degrees of toxicity. PCBs were very popularly used in a large variety of products due to their “non-flammability, chemical stability, high boiling point, and electrical insulating properties” (EPA). Some examples of products listed on the EPA’s website for things that previously contained PCBs include:
· Pigments and dyes
· Oil-based paint
· Carbonless copy paper
· Cable insulation
· Old electrical devices containing PCB capacitors
· Fluorescent light ballasts
· Floor finish
· Adhesives and tapes
· Oil used in motors/hydraulic systems
· Electrical equipment (i.e. voltage regulators, switches, electromagnets, etc.)
· Thermal insulation material (i.e. felt, cork, fiberglass, etc.)
And the list goes on!
What is Bioaccumulation?
Bioaccumulation is defined as “‘the net result of uptake, transformation, and elimination of a substance in an organisms due to all routes of exposure (i.e., air, water, sediment/soil, and food)’ and degradation as ‘the decomposition of organic molecules to smaller molecules and eventually to carbon dioxide, water, and salts’” (ScienceDirect).
Basically – bioaccumulation can be described as a build up of chemicals in fish as you move up the food chain. As you move up the chain, the accumulation of chemicals stored in the fish gets higher and higher – so smaller fish at the bottom of the chain have less built-up chemicals in their bodies, whereas bigger fish towards the top have more chemicals built up and stored within them. Accumulation of these chemicals will continue to occur all the way up the food chain, becoming more and more concentrated as you go up each trophic level, and this includes our mammalian top predators. This, then, can impact the top predators that commonly eat these fish as a main part of their diet, such as many of our cetaceans, and means that they are the most vulnerable to their negative effects.
PCB Bioaccumulation and Cetaceans
PCBs are not easily degradable: they do not easily break down once in the environment. They can remain in things such as air, water, and soil for quite a long time – and therefore have been found all around the world, even in areas far from where they were initially released. They also can remain within organic material for a long time – and build up (accumulate) in organisms as you move up the food web (see previous section). Though banned back in 1979, we still see traces of this chemical that have persisted in various substances, organisms, and parts of the world today.
Being that many cetaceans (i.e. orcas, humpback whales, bottlenose dolphins, harbor porpoises, etc.) find themselves at the top of their food chains and feed on many fish, they can see the most intense effects and highest level of this bioaccumulation of PCBs in their marine ecosystem. What’s worse – not only are these apex predators seeing the highest concentration of PCBs in their bodies due to their high fish intake – but their blubber seems to be a well for these chemicals: PCBs seem to be greatly stored within the cetacean’s blubber and is retained in it for a very long time – meaning it just continues to build up within the animal’s stores of blubber. Although these chemicals were banned many years ago, concentrations still appear to be very high in cetaceans (i.e.: 1300 mg/kg lipid weight in orcas (Desforges et al. 2018)).
This is a problem for two reasons. First, when cetaceans go through periods of time with low food intake (i.e. migration), they rely on these stores of blubber to survive until they are able to feed again. This means that as their bodies begin to tap into these stores, they are quite literally being slowly poisoned by these PCBs as they are using their blubber. Secondly, this is causing the mother’s milk to contain PCBs / placental transfer to occur, and so cetaceans that were never exposed to this chemical are being born with it already stored in their bodies and continued to be given to them through their mother’s milk.
So, why are these PCBs so bad?
According to the EPA, when found in high concentrations (like we can see in many populations of cetaceans that live near urbanized areas), we can see negative impacts such as:
· Reductions in the immune system
o Increased vulnerability to diseases and illnesses
· Reproductive effects
o Reduced conception rate
o Reduced birth size
o Developmental abnormalities
· Endocrine disruption
o Thyroid hormonal levels – critical for growth and development
· Neurological effects
o Deficits in neurological development
· Other effects
o Liver toxicity
o Elevated blood pressure
The buildup of these effects has produced population declines in those that have high concentrations of PCBs accumulated within their system (on top of all of the other stressors cetaceans are facing in today’s age). One example of this can be seen in orca populations (who eat both fish and blubber-containing seals and therefore take in a high amount of bioaccumulated PCBs) in regions where PCBs used to be used widely, such as Brazilian, Hawaiian, Japanese, Greenlandic, and U.K. populations (Desforges et al. 2018). According to Desforges et al., these populations are “at high risk of collapse over the next 100 years”. The loss of cetacean populations around the world would not only be a tragedy, but would cause great environmental impacts as well, such as whole trophic cascades.
While the outlook may look grim, there is still hope for many of our cetacean populations. While PCB-containing / PCB-contaminated products are no longer being produced, there are still many that have still not been properly disposed of. Ceasing to use these products, as well as holding businesses/countries accountable for the proper disposal of them can prevent more PCBs from entering our marine ecosystems, and begin the slow process of the decline of PCBs within our food webs. Further management of these PCBs and their disposal is critical.
One thing to note is that cetaceans are at the top of their food chains – another top predator that feeds on many higher trophic-level fish is us humans! In communities that eat a lot of these fish that have bioaccumulated high concentrations of these PCBs, accumulation of these chemicals can be seen in people as well. This can cause similar negative impacts to people as those discussed earlier in this article. So – although this problem is very important for the health of these cetacean populations and the ecosystems they inhabit – this is also an issue that is important in human society as well.
-Summer Eckhardt, Intern at Cape May Whale Watch and Research Center
Michigan State University ’22
“Bioaccumulation.” ScienceDirect. 2021. https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/bioaccumulation
Desforges et al. “Predicting global killer whale population collapse from PCB pollution.” Science. 28 September 2018. https://science.sciencemag.org/content/361/6409/1373
Genov, Tilen. “The impacts of chemical pollutants on cetaceans in Europe.” Morigenos – Slovenian Marine Mammal Society.https://www.oceancare.org/wp-content/uploads/2021/04/UNDER-
Jepson, Paul D. et al. “PCB pollution continues to impact populations of orcas and other dolphins in European waters. Nature. 14 January 2016. https://www.nature.com/articles/srep18573
“Learn about Polycholinated Biphenyls (PCBs).” United States Environmental Protection Agency. 2021. https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs
Tanabe, Shinsuke et al. “Capacity and mode of PCB metabolism in small cetaceans.” Wiley Online Library. April 1988. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-7692.1988.tb00191.x
“What are PCBs?” NOAA. 5 April 2021. https://oceanservice.noaa.gov/facts/pcbs.html
“What is bioaccumulation?” Michigan Department of Community Health. https://www.michigan.gov/documents/mdch/Bioaccumulative__Persistent_Chemicals_FINAL_354016_7.pdf