It is clear that we cannot live without plastic anymore. Plastic has become an essential material for our life, from the moment we get up at the morning (such as in our toothbrush, the eyeglasses we wear, the myriad of toiletries we have, the plastic film we use to wrap our sandwich) or when we are at work (the PC, the coffee capsules we often drink, the container our lunch is in) or shopping (do you notice how food is meticulously packed up in the supermarket?).
It is quite evident that the use of plastic has revolutionized fields such as the medicine or industries since John Wesley Hyatt invented it in 1869. Indeed, in Europe alone, more than 1.5 million people are working in the plastics sector, and if we have a look at the world of plastic manufacturing, its production has exponentially grown from 1.5 million metric tons in 1964 to 335 million metric tons in 2016. Consequently and due to its mismanagement, we can find plastic debris in the most unsuspected places, such as the abysses of the ocean (the Mariana Trench in the Pacific Ocean), the farthest oceanic point from land (Point Nemo, South Pacific Ocean), the Arctic Sea ice, or in the table salt we use at home.
But plastic is not an inert material. This means that plastic can leach some of its components to the surrounding environment. The point is that plastic is composed of different kind of polymers, some of which are known to act as Endocrine Disrupting Chemicals (EDCs). The EDCs are man-made chemicals, found not only in plastics but also in pesticides or personal care products, which can interfere with our hormones and their receptors and then may alter the levels of hormones, i.e. estrogens or testosterone. Let’s say that these types of chemicals can “mimic” some hormones and trick our body thinking we have more or less quantity circulating in our blood. Indeed, the EDCs have been linked to several clinical disorders such as reproductive dysfunctionalities, obesity and diabetes, altered development, or some kinds of cancers.
Traditionally, the effects of EDCs have been studied in murine models (rats or mice), but a recent study conducted by Forner-Piquer and colleagues studied this phenomenon in an interesting marine species, Sparus aurata, more commonly known as the gilthead sea bream. The gilthead sea bream is a tasty fish, intensely farmed in the Mediterranean Sea, and highly appreciated by consumers. It is a very fascinating species since it is a sequential hermaphrodite, which means that it begins its life as male only to become female when they are two or three years old. Due to this particular feature, the gilthead sea bream is a potential new species to study how chemicals may interfere with the hormonal system as the EDCs do.
The work was based on the study of two common EDCs found in daily plastic items such as plastic bottles, artificial leather, resin coating of canned food, or perfumes: Bisphenol A (BPA) and di-isononyl phthalate (DiNP). Bisphenol A is one of the most produced EDCs, and it can leach from the container into food or liquid. Its estrogenic effects have been known since 1938. Regarding DiNP, it is essential for PVC manufacturing and is considered to be an “environmentally-friendly phthalate.”
Since BPA and DiNP can be potentially introduced into the food as previously mentioned, the researchers added those pollutants to fish food, so that the fish received a precise daily dose of chemicals with their meal. For humans, the presence of such EDCs in plastic items is tightly controlled by different regulatory organisms such as the European Chemicals Agency (ECHA) and the European Food Safety Authority (EFSA). Through the revision of several scientific studies, both groups have established a “safe” percentage of EDCs, i.e. BPA and DiNP, that a plastic item can contain or the daily amount of the chemicals we can “safely intake” every day.
After the chronic treatment, the researchers saw that the gilthead sea breams’ liver increased in fat content and their hepatic cells lost their typical shape, becoming more spherical because of the accumulation of fat. In addition, through infrared microspectroscopy, it was confirmed that the content of hepatic lipids and triglycerides increased in the treated fish respect the non-treated fish, even when all the groups ate the same quantity of food.
Additionally, the endocannabinoid system was studied. The endocannabinoid system, named for the plant (Cannabis) that led to its discovery, has emerged as a cell-signaling system with an important homeostatic role to maintain human (and non-human) health. Indeed, when the levels of endocannabinoids are deregulated, it is the starting point for several disorders, i.e. obesity or fatty liver disease. Then, as a new ecotoxicological endpoint, the team studied the basic components of the endocannabinoid system (the messengers, the receptors, and the biological catalysts, the enzymes).
The results were interesting since the levels of endocannabinoids were completely deregulated after the treatments in the liver and in the brain, probably due to the deregulation of the endocannabinoid enzyme activities. As we mentioned above, the deregulation of the endocannabinoid can lead to fat accumulation in the liver and the alteration of metabolism; while in the brain, the endocannabinoid system, interacting with appetite hormones, is involved in food intake control, meaning our desire to eat.
Even further, in addition to the physiological consequences of BPA and DiNP ingestion, both chemicals also altered the genes involved in lipid metabolism and in the endocannabinoid system, having an effect at the transcriptomic level, or the genetic level.
The study concluded by showing that both pollutants disrupted the lipid synthesis pathway leading to an increase in hepatic fat and deregulation of the endocannabinoid system. It must be noted that it is quite concerning that only a 21-day trial was enough to induce such concerning alterations in the liver of gilthead sea bream. Thus, if we realize that BPA (plastic) exposure is considered almost chronic for humans, and if we understand that EDCs are linked to several health disorders, and considering that 60-80% of marine litter is plastic, while knowing that plastic has been found in stomachs of over 220 different marine species (FAO reports) and that 8 millions tons of plastic end up in the ocean every year… something has to be done.
These findings are described in the article entitled Endocrine disruptors in the diet of male Sparus aurata: Modulation of the endocannabinoid system at the hepatic and central level by Di-isononyl phthalate and Bisphenol A, recently published in the journal Environment International. The work was conducted by Isabel Forner-Piquer, Francesca Maradonna, Giorgia Gioacchini and Oliana Carnevali from the Polytechnic University of Marche (Italy), by Constantinos C. Mylonas from the Hellenic Centre for Marine Research (Greece), by Josep Calduch-Giner and Jaume Perez-Sanchez from the Spanish Research Council (Spain) and by Marco Allara, Fabiana Piscitelli and Vincenzo Di Marzo from the Italian Research Council (Italy).
The work received funding by the Progetti di Relevante Interesse Nazionale (PRIN) from the Italian Government and from the European Union’s Horizon 2020 research and innovation program under the TNA program within AQUAEXCEL2020 project.