The world’s oceans are a global reservoir of persistent organic pollutants to which humans and other animals are exposed. A new study has found that fish tainted with common, long-lasting environmental contaminants weaken the human body’s ability to defend itself against toxins.
Persistent organic pollutants (POPs) that are resistant to environmental degradation will soon have very significant impacts on human health with some scientists estimating that almost 50% of all babies worldwide will have at least one birth defect.
“This is a serious concern,” said Dr. Marvin Eastman from the Tobias environmental research centre in New York City. “According to our research, in less than two decades the exponential rate of increase of POPs around the world will soon prevent almost half of newborns worldwide from developing normally and with at least one birth defect.”
Although it is well known that these pollutants are potentially hazardous to human and environmental health, their impacts remain incompletely understood.
Studies show that eating the POPs-contaminated farmed salmon led to greater weight gain and higher predisposition to type 2 diabetes compared to a salmon-free diet with the same amount of total fat.
Ocean pollutants that may contaminate our food are able to tamper with the body’s ability to cope with toxins. The finding makes it more urgent to know how the pollutants act, especially as they are often found in combination.
POPs have been found almost everywhere on Earth, from remote islands to all oceans, and in the bodies of killer whales off the coast of Europe. They have been implicated in the global die-off of honeybee colonies.
Amro Hamdoun and Sascha Nicklisch at the University of California at San Diego and colleagues studied 37 organic pollutants and their effect on P-gp, a cell-membrane protein that recognises harmful molecules and boots them out.
They identified specific congeners of organochlorine pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers that inhibit mouse and human P-gp, and determined their environmental levels in yellowfin tuna from the Gulf of Mexico.
In experiments on yeast cells expressing the mouse P-gp protein, 16 of the pollutants stopped it from working. Ten of these chemicals have been found in humans, implying they are in the food chain.
One of these is the pesticide DDT, which was banned by an international treaty in 2001. Others include chemicals used as industrial flame retardants.
The results demonstrate the potential for specific binding and inhibition of mammalian P-gp by ubiquitous congeners of persistent organic pollutants present in fish and other foods, and argue for further consideration of transporter inhibition in the assessment of the risk of exposure to these chemicals.
“P-gp is incredibly important for eliminating a wide range of drugs and toxins,” says Hamdoun. “These widespread pollutants can inhibit this defence system.”
Newborn babies may be among the most vulnerable to the toxic chemicals, since organic pollutants reach high concentrations in breast milk and infants have low levels of P-gp in their cells.
The pollutants usually appear as mixtures both in the environment and in our food, says Nicklisch. “We don’t know what effects the combined levels of these inhibitors will have on the body, particularly when taken together with other medications.”
There should be more testing on pollutants to determine their effects on biological defences against toxins, the researchers say.