Road salt’s second sting

This is an article I wrote that published in the Charlotte Observer and Raleigh News & Observer’s Sci-Tech pages on Nov. 14, 2011. 

Marbled salamander, photo courtesy of Jim Petranka.

A sure sign that winter has arrived is when drivers spot chunks of road salt in their lanes. It’s safe to say drivers appreciate ice-free roads, but … ever wonder where all that salt ends up?

In North Carolina, the Department of Transportation spreads, on average, 256,249,901 pounds of salt on state-managed roads each year.

UNC Asheville biologist James Petranka decided to investigate what this seasonal onslaught means for our native amphibians. Because amphibians breathe through their skin and are highly susceptible to environmental contaminants, Petranka wondered if flushes of road salts to their breeding ponds kill them.

The salt, he learned, didn’t kill the amphibians outright, though it does harm their growth as juveniles. Perhaps more alarming, he found the road salt is causing problems in the food web.

Mimicking nature

The effect of road salts on lakes and streams is documented, but it’s understudied in pools that form seasonally, and seasonal pools are where amphibians prefer to breed in late winter and early spring. After reading a scientific report on road salt effects upon wood frogs and spotted salamanders in the Adirondack Mountains of upstate New York, Petranka couldn’t get his mind off what might be unfolding in the mountainous woods of Western North Carolina that surround his office.

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Frogs and atrazine

What’s causing amphibian declines? Atrazine exposure? Chytrid fungus? Loss of habitat and climate change? All four elements working synergistically? Science News recently ran an in-depth feature re-examining the risks of atrazine, one of the world’s most widely used agricultural pesticides. In this piece, “Weedkiller in the cross hairs” by veteran science writer Janet Raloff, I learned that the largest U.S. producer of atrazine — Syngenta Crop Protection — is 30 minutes down the road from me, in Greensboro, N.C. Her article tussles with the various angles of whether exposure to atrazine in a laboratory setting can accurately model effects of the chemical upon wild amphibians, but one bit of reporting that  made my heart drop was a USGS map delineating where atrazine was predicted to occur based on watersheds and monitoring data. Check it out:

USGS map modeling atrazine concentrations in stream water, in 2007.

The red areas indicate concentrations exceeding 1.026 micrograms per liter (same as parts per billion measurement). I find it really curious that what appears to be Charlotte is an atrazine hot spot in my state. Why not the Piedmont of N.C., where lots of corn, soy and vegetable farming occurs? Why would it accumulate in an urban area? (Do you know? Comment section is always open…) And I can’t help but wonder why there is no data for the area south of Lake Okeechobee in Florida, where large tracts of sugar cane and vegetable  farms have bled phosphorous and nitrogren into the Glades for years and years. It would not be a huge leap of logic to hypothesize that pesticides too are leaking south in this area.

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