Are plastic eating fish Top Of The POPs?
Eight million tonnes of plastic enter the ocean each year, that’s one tonne every four minutes. At current rates plastic is set to outweigh the amount of fish in the ocean by 2050, coincidently the same year that scientists predict all sea birds will contain plastic.
Although slightly different in their composition (PET, PVC, PCB etc), most plastics are made from an array of, usually toxic, chemicals that can leach into the environment and find its way into animal tissue. In addition to releasing their chemicals to the environments, plastics also accumulate nasty toxic chemicals from the environment around them. These chemicals, also known as Persistent Organic Pollutants, can cause huge amounts of damage to biological organisms (and yes, that includes humans).
Top of the POPs
So what exactly is a POP? Well, POPs are Persistent Organic Pollutants and are resistant to chemical, biological and photolytic (solar) breakdown, this means that they stay in the environment for years. POPs also have a tendency to accumulate in fatty animal tissue and all are toxic to humans and/or other animals. Maybe not surprisingly, most of POP ‘hits’ have been produced directly by humans or as a by-product of another human process (anyone who used to watch the greatest live chart music show from the UK might get that pun).
Check out this weeks top twelve POPS:
The impact of POPs is so large that they were described as a global issue needing international collaboration, this was recognised by the formation of the Stockholm convention in 2001.
But there is something even fishier about POPs…
It is known that Persistent Organic Pollutants can accumulate in fish and be transferred to humans. Lactating mothers who are subjected to POPs, for example through eating fish, can pass on these detrimental, carcinogenic compounds to their infants through breast milk.
Now new research shows that POP can bio-accumulate in fish and interrupt normal human immune defences. The research focused on important human immune system cell surface protein, P-glycoprotein (P-gp). This is a special protein that exists in all animals, fungi and even bacteria cells. It is present in the cell membrane and it pumps out harmful toxins. In humans P-gp proteins are found mainly in the intestines, liver, kidneys and the capillaries, pumping foreign chemicals out of cells. They are also known for removing therapeutic drugs from cancerous cells, obviously this isn’t exactly what we would want but this shows how seriously these P-pg cells take their job.
So it’s safe to say that these proteins are important in regulating our exposure to toxins and therefore pretty important in our immune response. Knowing that POPs inhibit these proteins should set alarm bells ringing. Marine species are already subject to these toxins in the water and they transfer these chemicals to humans.
Worryingly these POPs can bioaccumulate, meaning more accumulate in top predator species, for example humans!
So what’s the link to plastic again?
One of the problems with POPs is that they can accumulate on plastic particles to even greater concentrations than in the environment around them. In fact the concentration on the particles can be over a million times greater than the surrounding water.
Ingested plastic, and the leaching of its toxins and associated toxins (i.e toxins that have accumulated on the particles such as POPs), can cause physiological damage to fish. Toxins, such as mercury and PCBs, have been found to move from plastic particles to animal tissues. On Lord Howe island in Australia the shearwater population there have mercury levels 100 times those known to be toxic, and this increase in toxic load is due to the high levels of plastic they ingest. Plastic has been seen to transfer into the blood stream of mussels, again another important commercial food source for human consumption. Plastics have been found in the soft tissue of mussels cultured for human consumption and, although it is hard to measure the toxicity, it is thought that these shellfish can consume about 11,000 micro plastics each year. More important reasons why we need to keep plastics out of the ocean, as well as thinking about what other pollutants might be in there.
Anyone interested in this subject area might find pellet watch an interesting resource as well as the other resources listed below. If you can’t access any literature, e-mail the listed authors and they should send a copy to you. Also here’s a great video about plastic, that includes a part about toxic contaminants found in plastics. Being educated, informed, and asking questions is one of the most powerful things we can do! We can demand better and we can change our own behaviours too.
References
http://www.ncbi.nlm.nih.gov/pubmed/20865254
http://www.nature.com/articles/srep03263
http://www.sciencemag.org/news/2015/02/here-s-how-much-plastic-enters-ocean-each-year
POPs
http://rstb.royalsocietypublishing.org/content/364/1526/2027 (Transference of toxins to sea birds and the environment)
http://www.sciencedirect.com/science/article/pii/S0025326X1100316X (absorption of toxins onto plastic)
http://pubs.acs.org/doi/abs/10.1021/es303700s (absorption)
http://pubs.acs.org/doi/abs/10.1021/es3027105 (chemical load and accumulation)
More info about POPs
Contributor: Jennifer Cooper