Standing on a gravel beach just south of the Chinatown Restaurant on the Bedford Basin on a warm day in October, Camille Coray bends down to look between the rocks. She’s surrounded by snails, but the one species she’s looking for in particular is missing.
Coray is studying the whole harbour ecosystem for her Masters degree, but today, she’s focusing on one thing—the absence of dog whelks, a native species of predatory snail.
“I can’t show you what a dog whelk looks like here, because there are no dog whelks,” says Coray.
The dog whelks are AWOL because of tributyltin, she says.
“Tributyltin is incredibly effective,” she chirps. “It kills everything!”
TBT, used as a fungicide in lumber and in the manufacture of plastics such as PVC, does the most damage when it leaches from marine paints on huge ocean-going vessels. TBT was banned in marine paints in 2003, but decades of use have left a legacy of contamination in the harbour.
The toxin, once used in marine paints to prevent barnacles and other sea creatures from attaching to the hulls of ships, disrupts the hormone balance in snails. This causes male parts—a penis and vas deferens—to “impose” themselves on the female genitalia
—a condition called “imposex.” In high enough doses of TBT, tissues relating to the male parts block the female snails’ genital openings. This means no sexual relations. No sex means no baby snails. In severe cases, once a female snail’s eggs are formed, they can’t be laid and the female snail ruptures and dies.
Coray is concerned because the snails are just the canaries in the coal mine. In sites with high imposex, she’s also seeing very little seaweed, lower numbers of native species and exploding populations of TBT-tolerant invasive species.
“There’s got to be toxic effects on other species that I’m not looking at, too,” says Coray, sifting through the snail shells, looking for dog whelks. “I’m not looking at every species there.”
In Bedford, one species of periwinkle— an invasive species of snail—and green crabs—another invader—dominate the beach and beyond.
“My theory,” says Coray, “is that these incredibly pollution-tolerant organisms say, ‘Woo-hoo! We can go crazy!’ And they do go crazy and even if some of those species are able to tolerate being here, once it’s been taken over by everything else there’s no room for them.”
TBT was hailed as a marine miracle when it was first introduced in the 1960s. The International Marine Organization, an agency of the United Nations, ratified an agreement banning the chemical for all anti-fouling purposes in 2002 and Canada signed on. TBT was completely banned in 2003.
But ships painted before 2003 still have TBT on their hulls and continue to leach it into the water. And any ship sandblasted and repainted at either shipyard in Halifax Harbour leaves paint chips containing TBT sitting in the water.
Environment Canada’s Gary Julien was part of a study in 2004 that looked at TBT concentrations in sediments in the harbour.
“When a ship goes into the dry dock over at the Irving Halifax shipyards and it gets blasted, although they have a protective screen there are huge holes to let the air go through, and that’s where we found the highest levels of butyltins,” says Julien.
Near the Halifax shipyards on Barrington, Julien and his colleagues measured concentrations of TBT 613 times higher than the amount needed to cause imposex. In comparison, the Dartmouth Marine slips, which closed in 2001, were 26 times more contaminated than the minimum levels that cause imposex.
Julien and Coray both agree that the chemical will take ages to completely disappear— that is, if it’s never brought into the harbour ever again. But with shipyards still sandblasting TBT-painted ships until 2008—when a total worldwide ban on any use of TBT-based anti-fouling paint takes effect and all ships have to have it removed—there will be a constant influx of the chemical.
“In ships with a normal coating, it’d be good for five to seven years,” said Julien of TBT-based paints, which had up to 15 percent of their dry weight made up by TBT. And research done by scientists in the Saguenay Fjord, a large, poorly-circulated harbour in northern Quebec, found it could take almost a century for the chemical to disappear from deep sediments.
“It’s very persistent. It’s a metal. It’s an element,” said Julian. “But since it’s got this complex associated with it, it stays in that state for quite some time.”
Regardless of the degeneration, the chemical is still used legally as a wood fungicide and in plastics manufacturing. So, when it rains, the chemical washes off treated wood, or leaches out of PVC pipes used in sewage and plumbing and runs straight into the harbour, untreated.
Miles outside Halifax in Duncan’s cove, beyond the plume of chemicals that flows out into the ocean from the city, Coray turns over a patch of healthy seaweed growing below the tide line. “Here’s one,” she says, smiling, and holding up a single, tiny, white-shelled dog whelk. She says all the little whelks here are normal and TBT is almost absent.
Despite her findings, Coray doesn’t think she’ll continue this research beyond her thesis. She wants to graduate and then work for an environmental consulting firm, where the research she does can “actually make a difference.”
In terms of her work in the Bedford Basin, she just wants to make sure future researchers have somewhere to start from when looking at the effects of TBT on the harbour.
“What I’m hoping to do is start something that will continue,” she says. “Even if someone doesn’t look again for another 10 to 15 years, at least there will be the data I’ve collected now and there will be some kind of baseline.”
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