Toxic SoCal Shark Contains 100 Times the Legal Limit of Chemicals Banned Decades Ago

posted: 07/16/15
by: Danny Clemens
Shortfin mako shark
Mark Conlin, SWFSC

A 1,300-pound shortfin mako shark recently caught off the coast of California was found to be contaminated with 100 times the legal limit of DDT and 250 times the legal limit of Polychlorinated biphenyl, a chemical once found in coolants.

Dichlorodiphenyltrichloroethane was thought to be a miracle substance throughout the first half of the twentieth century: it was widely used as both an insecticide and a pesticide, and was instrumental in controlling (and eventually eliminating) malaria in various parts of the world.

Now, we know a little bit more about the substance's long-term effects.

Better known as DDT, the possibly carcinogenic chemical has proven to be a harmful endocrine disruptor associated with pregnancy loss, hypothyroidism and decreased semen quality. DDT is a persistent organic pollutant, meaning that it is highly resistant to degradation in the environment. It can stay in soil for up to 30 years, and accumulates easily in the fatty tissue of wildlife.

Although the substance has been largely banned in the United States for several decades now, it's still present in frightening amounts in our wildlife.

The OC Register reports that a now-defunct chemical plant discharged massive amounts of the chemicals into Southern California waterways for more than 40 years. Because the chemicals are highly resistant to degradation, the shark spent much of its two decades on the planet accumulating the discharged toxins in its body.

Apex predators (like sharks) are especially susceptible to bioaccumulation: because the persistent pollutants accumulate in fatty tissue, a shark that eats a seal is also ingesting all of the pollutants from the seal's prior meals. The process continues down the food chain, all the way to plankton. Because a shark's liver is so oily, the shark has much more room to accumulate toxins than a less oily creature would.

Related: researchers recently autopsied a bird in Canada with such high levels of a banned flame retardant that it was dubbed "flameproof".

A study about the contaminated mako is published in the current edition of the Journal of Fish Biology.

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