There is a lot of information out there about the best foods to help us lose weight, prevent cancer, fight inflammation – the list goes on. In fact, for everything about our health we try and improve, there’s someone with a new theory on how to do it. But what does the science say?
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to give you the evidence-based approach to take the mystery out of the best way to live a healthier, longer life.
Today, it’s microplastics. And yes, they’re quite small. In fact they’re so small fish can eat them and well, you can guess where they end up. In our first story we try and determine if ingested plastic particles from fish can get into our bloodstream?
In 1869, a patent was taken out for a new substance to replace elephant ivory in the production of billiard balls, and the plastics industry was born. Ironically, what started out as a conservation-minded measure has turned into an environmental problem. Hundreds of thousands of tons of trillions of tiny plastic particles “are now floating on the surface of the sea.” This is how it works, either from plastic objects, like water bottles, that get worn down into tinier and tinier pieces, or plastic microbeads flowing down into the sewers from our sinks.
“Plastic microbeads are often used as a scrubbing agent in personal care and cosmetic products, such as facial cleansers, shower gel and toothpaste,” and “up to 94,500 microbeads could go down the drain in a single wash.” Then, when you trawl the oceans, you can find the same beads you find in the facial scrubs. Billions “are emitted into aquatic habitats every day in the United States.” Laid end to end, the United States emits enough microbeads to “wrap around the planet” more than seven times.
The reason this may be a problem is that the plastic then accumulates toxic compounds from the water and then shuttles them, along with any chemicals originally in the plastic, “into marine organisms,” concentrating up the food chain, and eventually ending up on our plates. “The potential hazardous effects on humans” then evidently include “alterations in chromosomes which lead to infertility, obesity, and cancer.”
Wait; let’s take a step back, and review the evidence. Plastic gets into the oceans, but does it even get into the fish? Yes: “Microplastics have been shown to be ingested” by fish and other seafood. But: “Are we then actually eating plastic-ingesting fish? Yes, we are eating plastic-ingesting fish.” But don’t we just poop the plastic out?
Small enough microparticles may actually be able to get absorbed through the intestinal wall and into our bloodstream. This “uptake of ingested microparticles into small intestinal tissues and on to secondary organs has moved from being an anecdotal phenomenon to a recognized and quantifiable process.” But that’s in rodents. Just because it’s been demonstrated across a variety of lab animals, you don’t know if it happens in people…until you put it to the test. The closest we have is working with human placentas after childbirth, and what they found is that plastic microparticles could indeed “cross the placental barrier” from the maternal bloodstream. So, if it could get into a pregnant woman’s circulation it might get into her baby’s circulation as well.
The reason this is concerning is that plastic debris can be a source of toxic chemicals, both chemical additives in the plastic itself, and then pollutants the plastic sucks up from the water that can then be later released into the body. BPA is one of the chemical additives that can originate from the plastic itself. Given that BPA concentrations have been measured in plastic debris, microplastics “may be a major source of BPA in seafood.” But no one’s really looked into it…until now: “BPA levels in edible parts of seafood.”
Yes, “fish and seafood present one of the highest BPA contamination” levels. But is that just because they were looking at canned fish products, like tuna and sardines? Manufacturers may use BPA in the lining of food cans directly. Yes, “BPA may also leach from the plastic in oceans, causing a direct contamination of fish.” In fact, “some argue that the BPA environmental contamination in fish” could be worse than the BPA from the cans themselves, but you don’t know…until you put it to the test.
The BPA levels found in canned seafood, the highest levels were found in like tuna, cockles, sardines, and blue crab. But, these were all canned; so, you don’t know how much is from the can versus the seafood itself, until you look at non-canned seafood, and sometimes found even higher levels in some fresh mollusks, clams, flounder, and cod.
That’s not good, since plastics chemicals, such as BPA, “are known endocrine disruptors,” meaning known hormone disruptors.
In our next story, we discover how plastic particles may exacerbate the pollutant contamination of fish.
“Plastic debris in the sea is more than just an unsightly problem.” The concern is not so much discarded bobbing bottles, as tiny microplastic particles, raising questions about cancer. Wait; 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. Cancers had started growing around the cellophane. So, they tried slipping all sorts of different plastics under the skin of rodents, and they all could produce malignant tumors. And then, if you feed rats some plastic microbeads, up to 6 percent of the particles end up in their bloodstream within 15 minutes.
So, could all this microplastics pollution be one of the reasons we’re seeing an increased number of tumors found in wildlife? Perhaps the global increase in wildlife cancers should be 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 having 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, flame-retardant chemicals, “increasing their concentration by orders of magnitude. This process is then reversible, with microplastics releasing contaminants upon ingestion.”
So, plastic debris may “act as a vector, transferring persistent, bioaccumulative, and toxic substances from the water to the food.” “Plastics are known to concentrate pollution from water by factors of up to 1 million times” for example, for PCBs. In fact, that’s one of the ways environmental scientists sample for contamination levels: they use plastic to sponge up pollutants.
The concern, then, is that the plastic takes up all these toxins, and then goes and 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 eat 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 can 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 to four units a day (measured in picograms of toxic equivalents). The European Union came up with a smaller number, like no more than two a day on average, and in the U.S. we’re already past that. So, “there is some concern for toxicity from PCBs,” given the current levels of PCBs and plastic debris polluting the ocean. “There is no “room” for additional PCB body burden.” So, what can we do about it?
Well, we can practice the three R’s: 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 in cosmetics and personal care product 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.”
And finally today we ask, how many plastic particles per serving have been found in the fish muscle itself?
Microplastic pollution of our waterways may not just represent a threat to marine ecosystems but also to human health. “It is evident that we are exposed to microplastic pollutants in seafood,” which may create a food safety risk. But, is there some seafood less contaminated than others?
The first published study looked at mollusks. Eating an average serving of mussels, you consume around 90 plastic particles, whereas an average serving of oysters may contain only around 50. “As a result, the annual dietary exposure for European shellfish consumers can amount to 11,000 swallowed microplastics per year”, though we don’t yet know what kind of risk this would carry. Of course, “due to their “persistent nature, microplastic abundance” is only going to get worse.
“It is inevitable that humans eating seafood will ingest at least some microplastics, particularly when the entire creature is consumed, such as mussels, oysters, and small fish. So, what, like sardines? We didn’t know… until now. “Contamination with microplastics and mesoplastics,” which are like little pieces of plastic larger than a millimeter. They looked at 20 brands of canned sardines from 13 countries over four continents, and only found plastic particles in about one in five. They suggested the disparity may have been due to improper gutting in the contaminated samples. But in mammals, at least, ingested microplastics can get through the gut wall and circulate throughout the body, and even cross the placental barrier. So, do microplastics actually make it into the muscles of fish, like a fish fillet? Let’s find out.
If you compare the level of microplastics in eviscerated flesh versus the organs, surprisingly, sometimes the flesh actually contained higher microplastic loads than the excised organs, which highlights that evisceration does not necessarily eliminate the risk of microplastic intake by consumers. Microplastics of all “colors, shapes, and sizes were detected in all investigated fish muscle samples.” So, they do actually get into the flesh. So, the average intake of microplastics from eating flathead, grouper, shrimp, scad, or barracuda may be in the hundreds per 300 gram serving, or just in the dozens of plastic particles in a two-ounce child serving. Besides the plastic itself, the particles may release absorbed pollutants like PCBs, and also release plastics chemical additives like BPA, which collectively may cause hormone disruption, cancer risk, and DNA damage. “Hence, although there is no standard tolerable dose for microplastics ingestion as well as information on exact toxicity of different plastic types in the human body, taking weekly servings of these kinds of fish may threaten the health of consumers (especially vulnerable groups including pregnant and breastfeeding women and children).”
In the US, “anthropogenic debris,” meaning man-made materials, were found in a quarter of individual fish and in two-thirds of all fish species tested, and also about a third of individual shellfish samples, demonstrating that “man-made debris has infiltrated” the aquatic food chain “up to the level of humans via seafood. Because this debris is associated with a cocktail of pollutants, this validates the concern that the “debris may be transferring these chemicals to humans via diets containing fish or shellfish, raising important questions regarding the bioaccumulation and biomagnification of chemicals, and consequences for human health.” Now, this study also included non-plastic debris, like foams, film, and fibers, but we know now that the ingestion of microplastics “appears to be a widespread and pervasive phenomenon” across a number of commercially important mollusks, crustaceans, and fish.
So: “The potential for humans, as top predators, to consume microplastics as contaminants in seafood is very real, and its implications for health need to be considered. Despite the existence of considerable uncertainties and unknowns, there may already be a compelling case for urgent actions to identify, control, and, where ever possible, eliminate key sources of microplastics before they ever make it to our oceans.”
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