The Mercury Connection: Is Plastic Debris Poisoning our Food Supply?

By April 6, 2011 Ocean News

Author: Arlo Hemphill

We’ve all heard the arguments on why plastic is bad for the ocean. Disposable plastics, set adrift on ocean currents, are mistaken for a food source and subsequently choke, maim, strangle, entangle and cause lethal indigestion to charismatic ocean wildlife such as sea turtles, marine mammals and sea birds. We’ve also been frequently reminded that it’s an eyesore on our beaches and that this pollution is accumulating in the Central Pacific in the form of a great swirling patch of garbage two times the size of…[insert your favorite large U.S. State here].

Plastic debris threatens our oceans and our health. Credit: "Sarah Lardizabal/ Marine Photobank"

Something less frequently addressed yet insidiously more dangerous to the health of humans is the role of plastics in transporting toxins into our food supply. We know that this is the case with hydrophobic (water repelling) organic contaminants such as PCBs, DDT and various other pesticides. But might it also be true of the worst toxin of all – mercury? You’ve likely heard warnings against the over-consumption of large, predatory oceanic fish due to concerns on mercury poisoning. The U.S. Food and Drug Administration, in response to this concern, recommends limiting canned tuna consumption to twice a week and advises pregnant women to avoid high-mercury fish altogether.

But where is this mercury coming from? And how is it getting into fish living in the middle of the ocean?
What if our own plastic garbage is one of the primary agents in transporting this toxin through the food chain and back to us? Are we literally poisoning ourselves and our children?

Hold on. Wait a second. There’s no mercury in plastic. Right? Surely we wouldn’t drink from plastic bottles and hand off plastic toys to babies if this were the case? So what’s the connection – how could plastic possibly be at fault for this global scale poisoning?

Sushi-grade tuna is believed to have some of the highest mercury-levels of any food fish. "Stephen McGowan, 2006/Marine Photobank".

Here’s how it might work. Over 11,000 tons of mercury are released into the atmosphere each year through both natural degassing as well as contamination derived from the burning of coal and waste, mining and other industrial processes. This airborne mercury eventually falls into surface waters, accumulating in streams and oceans, where bacteria transform it into methylmercury – a hydrophobic organic compound. From here, scientists believe a percentage of it is absorbed through the gills of fishes. As one slightly contaminated small fish consumes another, this mercury works its way up the food chain and bioaccumulates – increasing to toxic levels in the largest and oldest of predatory fishes. On the other hand, we also know that the smaller fish and invertebrates at the base of the food chain are consuming copious amounts of plastic debris, particular orange to red colored fragments that they’re likely confusing for small crustaceans and other natural prey. These ocean-drifting plastics are contaminated with adsorbed toxins – the hydrophobic organic compounds that don’t mix well with water, but readily cling to petroleum-based plastics. In fact, they seem to greatly “prefer” this substrate to any naturally-occurring sediment or structure in the ocean. And we know that in the case of PCBs and some of the pesticides, their concentrations are higher on drifting plastic than the surrounding ocean water by several orders of magnitude. Tiny plastic fragments carrying these compounds around are in fact tiny toxic “bombs”, just waiting to be gobbled up and injected into the food chain. While much of the research on this has focused on PCBs and pesticides, methylmercury, which regularly coincides with these chemicals in contaminated sediments, is also hydrophobic and likely to behave in a similar way – adsorbing onto plastic in preference to sea water or naturally occurring solids in the ocean. Thus, plastic may be playing an amplifying effect – collecting and concentrating the most lethal of toxins, and transporting directly into the human food supply.

Mercury is both the most toxic metal and the most powerful neurotoxin. It binds to our fat-soluble neurological tissue and bioaccumlates in our bodies in the same way it does in fish. It passes regularly across the placenta and into breast milk. Signs and symptoms of mercury exposure include irritability, fatigue, depression, memory loss, anxiety, decline of intellect, drowsiness, tremors, blurred vision and insomnia. It causes heart disease, cancer and reproductive system damage. In prolonged and higher doses it is lethal.

So how do we protect ourselves and our families? Here are a couple actions we all can do:

1) Engage your elected officials to reduce the legal limits on mercury released into the environment through industrial activities.

2) Reduce, reuse and recycle all plastic materials. Take individual responsibility that plastic never gets into the ocean

3) Lower or eliminate your consumption of large, long-lived ocean predators. Sushi grade tuna in particular is believed to have the highest mercury levels of any food fish. Salmon and mahi mahi are comparatively safer in that they are fast growing fish, generally consumed at younger ages.

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