The production of plastic increased from 500,000 tons in 1950 to 322,000,000 tons in 2015 (Thompson et al. 2009, PlasticEurope). As of 2012, approximately half of this plastic has been discarded as waste and some of it has spilled into the ocean (Rochman et al. 2013).
There has been a lot of research into the accidental ingestion of plastic waste as well as into plastic waste entangling marine animals over the past few decades (Kühn et al. 2015). Recently, however, the toxic chemical substances that adhere to the plastic waste have become a serious issue (Rochman 2015).
Plastic marine debris contains various kinds of chemical substances, which are added when the plastic was produced or come from its final product or have been taken up from the sea water. Therefore, this is referred to as a “cocktail of chemical substances” (Rochman 2015).
When plastic is produced, “additives” are added as these provide many functions. There are many kinds of additives, including stabilizers, plasticizers, flame-retardants, UV-stabilizers, etc.
It has been shown in animal tests that bisphenol A (BPA) and phthalate plasticizers, which are the raw material of polycarbonate, have a carcinogenic effect or act as endocrine disruptors, which harm reproductive function, even in low concentration (Crain et al. 2007, Oehlmann et al. 2009, Halden et al. 2010, Meeker et al. 2009, vom Saal et al. 2007, Hauser & Calafat 2005).
Flame-retardants are often added to make it difficult for the plastic to burn, such as for fire prevention. However, brominated flame retardants (PBDEs) are often used, which have thyroid disrupting effects and exhibit neurotoxicity and are well known as a toxic persistent organic pollutant (POP) (Oehlmann et al. 2009, Halden et al. 2010, Lithner et al. 2011).
Furthermore, DEHP (Di(2-ethylhexyl)phthalate) and DINP (Diisononyl Phthalate) are often used as plasticizers to produce polyvinyl chloride (PVC), which is used for synthetic leather and PVC pipe. An experiment using Daphnia proved that these phthalate additives have an acute toxicity (Lithner et al. 2012).
The additives which contain these dangerous substance are dissolved from the plastic in the water. However, if the additive is highly hydrophobic, it will not be dissolved while drifting in the ocean and spreads while remaining in the plastic (Crain et al. 2007, Lithner et al. 2012, Yamashita et al. 2016).
Therefore, when marine animals accidentally eat plastic, mistaking it for food, these harmful additives enter their bodies (Rochman 2015).
It is a possible scenario that when animals eat plastic containing a toxic chemical substance, there is bioconcentration throughout the food chain. Currently, not enough research has been conducted to determine how much harmful additives would affect humans or animals at the top of the food chain.
Furthermore, plastic waste, that “cocktail of chemical substances”, contains several kinds of chemical substances. This cocktail these may have significant negative effects, and it is urgent that research be conducted in this area to assess these (Rochman 2015).