Team:Chalmers-Gothenburg
BBC: Seal pups 'at risk from toxic chemicals in contaminated water' (2018) , National Geographic: Half the World's Orcas Could Soon Disappear—Here's Why (2018)
PCB - A global problem
Polychlorinated biphenyls, PCBs, are a group of chemicals that were used extensively between early 1880s and late 1970s. The structure of PCBs gives them a variety of useful properties, and for almost a hundred years they were used in many different applications. PCBs are not flammable, have useful electrical properties and are, most importantly, extremely stable. Their stability is both what made them useful and also what make them a problem today. Today, over 30 years after they were effectively banned, their toxicity still affects both humans and other animals.
Inspiration
Delsjön is part of Gothenburg's fresh water reserve. Not far from here is an old dump, which run-off water contains PCB.
We wanted a project that inspired us, and we quickly discovered that an environmental project engaged all group members. Our project was partly chosen because of the local connection. Around our hometown, Gothenburg, there are locations that have high concentrations of PCB and several animal species in Sweden have been on the brink of collapse, because of PCB and DDT contamination. These factors and existing enzymatic pathways, for the breakdown of PCB, made it the perfect project for our iGEM team.
Solution
Our idea was to take genes from various bacteria, able to degrade PCBs, and incorporate them into the yeast Saccharomyces cerevisiae. After research, a set of genes that could degrade even the most persistent PCBs were found.
Modeling
In order to get an understanding of our enzymatic pathway and its viability, we added hundreds of reactions for the breakdown of different types of PCBs, to a genome scale metabolic model of S. cerevisiae.
Human Practices
In order to make the most of our project, our team engaged with local experts in ecotoxicology, water cleaning, fishing industry and more. We acquired more knowledge on the potential applications and problems and changed our project thereafter.
Further Reading
Continue exploring the different parts of our project by clicking on one of the images below!
Get an overview of our project in Project Description, or delve straight into the details of it in Project Design. Check out how we simulated the degradation of PCB in Modeling, or go to Integrated Human Practices, where we have collected experts' opinions that influenced our project along the way. In Education & Engagement you will find the different ways we aimed to inspire and educate our community, whereas the Collaborations page explains how we helped and were helped by other iGEM teams. If you want to see the details of what we did in the lab, go over the protocols used for the different types of Experiments performed, or scroll through all of the 4 months of lab work documented in Notebook. You could also read up on the details of the different Parts used, or go straight for the actual Results of all our hard work. Under Contribution we have documented how we contributed to iGEM by further characterizing already existing BioBricks, while Safety will take you to the details of how we made sure to keep ourselves and others safe in the lab. If you are curious about the people behind the DePCB project, head over to our Team page! Or better yet, check out the real heroes under Supervisors. Lastly, we do not want to forget to give credit where credit is due, so please see our Attributions page, where we aim to say thank you to the people who deserve it, and check out our Sponsors who helped make this project possible.
Human health
Because of their persistence, bioaccumulative properties and toxicity, PCBs are a global concern regarding human health. High levels of PCBs are associated with reduced fertility and hormonal disturbances in the thyroid gland. It is also suspected that high levels of PCBs can cause increased risk of certain cancer types and affect brain development, as well as the nervous- and immune systems. Developing fetuses and babies are especially vulnerable to the effects of PCBs, which can cause them lifelong damage.
Although PCBs were banned in the 70s, humans are still exposed to them, and other dioxin-like toxic compounds. Because of our role in the food web, as the world’s absolute top predator, the toxins that accumulate in the food chain eventually end up in us through the food we eat. Babies are also exposed to higher concentrations though the mother’s breast milk. High levels of dioxins and PCBs have caused the Swedish National Food Agency to advise children and fertile women to not eat fatty fish, from the Baltic sea and the largest Swedish lakes, more than two to three times per year and the rest of the population should keep it to maximum of once per week.
References
- Wu J, Hu J, Wang S, Jin J, Wang R, Wang Y, Jin J. Levels, sources, and potential human health risks of PCNs, PCDD/Fs, and PCBs in an industrial area of Shandong Province, China. Chemosphere. 2018 May 1;199:382-9.
- Livsmedelsveket, Dioxiner och PCB. [Internet]. Livsmedelsverket.se. 2019 [cited 16 October 2019]. Available from: https://www.livsmedelsverket.se/livsmedel-och-innehall/oonskade-amnen/miljogifter/ dioxiner-och-pcb
Orcas
All over the world, the orca is known as a social species, forming families and packs. They have survived extensive hunting by humans, and exploitation of their natural environments, but they are now straining against a threat that cannot be seen by the naked eye: PCB pollution.
Recent research suggests that more than half of the world’s populations of orcas could face complete collapse in 30 to 50 years, due to PCBs; a chemical that was banned and has not been used on a wide scale since the 80s. The PCBs bioaccumulate in orcas over time, as they ingest it through their prey. Due to orcas being mammals, the toxin is also passed on to their calves during birth and through breast milk.
The PCBs are believed to already be altering the behavior of orcas, damaging their immune systems, and reducing fertility to an extent where many researchers suspect many populations will not survive the coming decades. Some orcas have PCB levels of 25 times the concentration that is considered fertility-altering.
PCB contamination is just one of several threats to the world’s orca populations and together they paint a black picture of the future survival of this majestic animal
References
- Welch C. Half the World's Orcas Could Soon Disappear—Here's Why [Internet]. Nationalgeographic.com. 2019 [cited 21 October 2019]. Available from: https://www.nationalgeographic.com/environment/2018/09/orcas-killer-whales-poisoned-pcbs-pollution/
Seals
Different species of seal are found in many oceanic waters, especially in colder regions. There are many different species, for example harbor seals are not an uncommon sight in the waters outside our home town, Gothenburg.
In the 50s the populations of seals declined rapidly, especially in coastal regions around industrialized countries, but it was not until the 70s that the decline could be attributed to the chemical compounds PCB and DDT.
PCBs accumulate in the fatty tissues of the seals, because of their hydrophobic characteristics. The role of the seals in ecosystems, as a top predator, makes these animals especially vulnerable, as toxins are accumulated throughout the food chain, vastly increasing the exposure for predatory animals. As a mammal, the seals also pass on high concentrations of PCsB to their cubs, through their breast milk.
PCB affects the seals’ ability to reproduce and also disturbs their immune systems, increasing the risk of sickness and epidemics in the populations. Although the populations rapidly started to recuperate and stabilize after the ban of PCBs in the 70s, they are still affected by the toxic chemical compounds. Recent research by scientists at Abertay University in Dundee, Scotland, has shown that the blubber, a vital organ for seals and whales, is affected at much lower concentrations of PCBs and DDT than previously thought.
References
- Fakta och statistik om PCB [Internet]. Naturvårdsverket. 2019 [cited 21 October 2019]. Available from: https://www.naturvardsverket.se/Sa-mar-miljon/Manniska/Miljogifter/Organiska-miljogifter/PCB/
- Seal pups 'at risk from toxic chemicals' [Internet]. BBC News. 2019 [cited 21 October 2019]. Available from: https://www.bbc.com/news/uk-scotland-46553454
Guillemots
The common guillemot is a species of bird present in many coastal regions in the northern hemisphere, for example in Sweden. It is just one of several bird species that have been, and still are, affected by PCB contamination.
In the 50s it was discovered that the populations of several coastal bird species were in rapid decline. Later, in the 70s, the decline could be attributed to high concentrations of PCBs and DDT. A high intake of these compounds cause a thinning in the birds' egg shells, making them fragile and causing them to break when tended to by their parents.
After the ban of PCBs, many of the affected populations started to recuperate, but the egg shell thickness has still not returned to normal levels.
References
- Sillgrissla - Världsnaturfonden WWF [Internet]. Världsnaturfonden WWF. 2019 [cited 21 October 2019]. Available from: https://www.wwf.se/djur/sillgrissla/#hotfylld-historia
Polychlorination
The many chlorine atoms on the PCBs make the chemical compounds extremely persistent. The fact that they are not broken down naturally causes humans and animals to still, to this day, be exposed to their toxicity, even though most production was banned in the 70s.
The chlorine atoms give the molecules hydrophobic properties, causing accumulation in fatty tissues. Sea living animals, like fish, and animals with sea food as part of their diet, or food chain, can thereby reach high concentrations of PCBs in their tissues.
References
- Porta M, Zumeta E. Implementing the Stockholm treaty on persistent organic pollutants. Occupational and Environmental Medicine. 2002 Oct;59(10):651–652.
- Welch C. Half the World's Orcas Could Soon Disappear—Here's Why [Internet]. Nationalgeographic.com. 2019 [cited 21 October 2019]. Available from: https://www.nationalgeographic.com/environment/2018/09/orcas-killer-whales-poisoned-pcbs-pollution/