 Plastic debris in the sea is more than just an unsightly problem. The concern is not so much discarded bobbing bottles, as tiny micro-plastic particles raising questions about cancer. What does plastic have to do with cancer? Back in the 1950s, researchers had observed that when they wrapped the kidneys of rats with cellophane to cause high blood pressure, they ended up inadvertently causing cancer. Head started growing around the cellophane, so they tried slipping all sorts of different plastics into the skin of rodents, and they all could produce malignant tumors. And then if you feed rats some plastic microbeads, up to 6% of the particles end up in their bloodstream within 15 minutes. So could all this micro-plastics pollution be one of the reasons we're seeing an increased number of tumors found in wildlife? Perhaps the global increase in wildlife cancer should be like a wake-up call. Now, we don't know if it's the plastic itself, or some of the chemical additives like BPA that are to blame. Maybe just the plastic particles stuck in your body causes some sort of mechanical irritation beyond the chemical impact of the plastics as carriers of possible carcinogens. Some plastics may be cancer-causing in and of themselves, but all plastics readily accumulate harmful chemicals, such as persistent pesticides like DDT, PCBs, and retardant chemicals, increasing their concentrations by orders of magnitude. This process is then reversible with micro-plastics releasing contaminants upon ingestion, so plastic debris may act as a vector, transferring persistent bio-accumulative and toxic substances from the water to the food. Plastics are known to concentrate pollution from water by factors of up to a million times, for example, for PCBs. In fact, that's one of the ways environmental scientists sample for contaminant levels. They use plastic to sponge up the pollutants. The concern then is that the plastic takes up all these toxins and then goes, deposits them into the aquatic food chain, where they can climb up the food chain and ultimately into humans, but this was all just theoretical. Until now, chemical pollutants glommed onto ingested microbeads from personal care products do indeed accumulate in fish. The longer you feed polluted microbeads to fish, the higher the levels of fish flesh contamination, so you can see how pollutant levels can then concentrate up the food chain with maximum exposure in the apex predators, like killer whales or people. The herring can eat a bunch of brine shrimp. Cod eats a bunch of herring, then halibut or tuna eat a bunch of cod, and then we can scoop it all up in the end. So we know ingested plastic can transfer hazardous chemicals to fish, which can then accumulate and cause liver toxicity and pathology in the fish, but what about in people? Well, we know that in the US, of all food categories, fish has the highest levels of PCBs, dioxins, and other pollutants, but we don't really eat a lot of fish in this country, so is it really a problem? Well, it's hard to come up with a tolerable daily intake of these kinds of chemicals, but the World Health Organization recommends staying under like one before a unit's a day, measured in picograms of toxic equivalents. The European Union came up with a smaller number, like no more than 2 a day on average, and the US were already past that. So there is some concern for toxicity from PCBs, given the current levels of PCBs and plastic debris polluting the ocean, so there's no room for additional PCB body burden, so what can we do about it? Well, we can practice the 3Rs, reduce, reuse, and recycle plastic items, for example, shopping with reusable tote bags. On a policy level, we could ban the use of plastic microbeads and cosmetics and personal care products, though ideally all countries would do it together, since plastic debris dropped anywhere on earth may end up being transported to the ocean, where it can travel around the world. So whatever strategies are adopted, international cooperation will be critical in limiting the risk to the oceans and the risk to humans from eating seafood.