(This is my column from Tuesday’s Monitor. Check out Geoff Foresters gorgeous photos of the loon chick here.)

Somewhere in the woods of Holderness or Sandwich, at the northern end of the lovely lake that inspired On Golden Pond, it’s likely that an abandoned barrel of unintended consequences is slowly killing loons.

And on the western side of the lake, along a dirt road named after a quaint local farm, a different set of unintended consequences is adding to the toll.

Between them, these oozing products of decades-old decisions help explain why Squam Lake is proving fatal to New Hampshire’s most iconic waterfowl.

“Loons are the canaries in the coal mine. It’s not just the loons, it’s everything. Everything might be affected,” said Tiffany Grade, a biologist with the Loon Preservation Committee.

The committee, which has been monitoring and trying to help New Hampshire’s loon population since 1975, is sounding the alarm on Squam Lake because just one loon egg hatched on the entire lake this year, a “new and very depressing low” for the population. It’s puzzling because the statewide population of the birds is fairly stable.

Puzzled, the Loon Preservation Committee started doing detective work. They took some eggs that never hatched from loon nests and tested them for a whole suite of contaminants. Eventually, they found two of real concern: PCBs and DDT.

Yes, DDT – the superbly effective pesticide that helped the world beat back malaria and other mosquito-borne diseases before we realized its unintended consequence, that it infiltrated the environment and was wiping out birds all over the globe. DDT was banned in 1972.

So how did it get into our loon eggs four decades later? The first idea is that it lingered in the lake, perhaps trapped in mud at the bottom, except for a molecular puzzle: Exposed DDT deteriorates over time and its chemical signature changes, but the DDT found in loon eggs is the same as brand-new DDT.

It’s extremely unlikely that anybody is manufacturing DDT these days and spraying it around Squam Lake. But there’s another possibility, which would occur to anybody who has walked through New Hampshire woods and stumbled across piles of metal, discarded and forgotten long ago.

“One option is that there are some old rusted barrels of DDT that all of a sudden released into the system,” Grade said. “That’s the most likely scenario.”

Finding the barrels won’t be easy. The Loon Preservation Committee is meeting this week with officials from the state departments of Environmental Services and Fish and Game to ponder the matter.

“We’re talking about: What’s the next step here? What do we do to discover what the source is? What are the mitigations for all of these sites?” Grade said.

So that’s one of the lake’s problems. Then, there is Coolidge Farm Road, which runs close to the west side of Squam Lake.

“We sampled the site in 2015. Subsequently there was a beaver dam blowout that washed out a culvert. We sampled the site again and PCB and dioxin levels had spiked 15 times just in one year – likely as a result of culvert work,” Grade said.

Why is a dirt road spewing out nasty organic compounds? Another unintended consequence of old decisions.

“They used to spray roads with oil to keep down the dust,” Grade said.

The oil usually came from companies like General Electric, who sold or donated it as residue from industrial processes. But those processes often meant the oil carried PCBs, dioxin or other persistent organic pollutants, which were ignored before everybody realized how bad those compounds are.

“They’re called persistent and they are persistent. They do not go away,” Grade said. Decades later, grains of dust and dirt in and around Coolidge Farm Road still carry some of that poison.

“We think what happened was, there was probably some sort of runoff event that pushed these contaminants out of the road sediment and it flowed into the lake. Loons are at the top of the food chain, so the contaminants get concentrated in them,” Grade said.

Organic toxins are often stored in body fat. In fall and winter, or during stressful times, the fat is burned for energy, at process that can release a burst of poisons into the system, killing the bird.

This is not unique. All around the country, especially in the Northeast, dirt roads once sprayed with used oil are slowly leaching PCBs, and there’s no easy fix. Digging up or paving all the affected roads, even if we could find them all, would be insanely expensive. So they will continue to ooze poisons for years and decades to come.

Admittedly, these poisons aren’t the only problem facing loons on Squam Lake and elsewhere. Lead fishing tackle is a real source of loon mortality – and may I take a moment to say that any fishermen who whine about spending a few extra bucks on non-poisonous tackle should have their rod and reel confiscated – while boat traffic can disturb nesting, and competition among loons themselves is an occasional problem.

But trying to control, if not eliminate, the source of these poisons can only help.

And it can only remind us that almost anything we do as an industrial society can carry unintended consequences, which may not show up for years. We shouldn’t be surprised, but we should be ready to react.

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