Lead in grizzly blood during hunt season
Researcher wonders if preliminary results show a danger to bruins from hunters’ bullets.
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By Cory Hatch Jackson Hole, Wyo.
November 12, 2008
Lead bullet fragments in offal piles could be poisoning Greater Yellowstone grizzly bears as they scavenge the remains of big game during hunting season, according to an ongoing study.
The preliminary data from University of Montana graduate student Tom Rogers echoes earlier studies on ravens and eagles from researchers at Craighead Beringia South, a research institution based in Kelly. Rogers formerly worked as a Craighead Beringia South wildlife technician.
Rogers checked blood samples of 24 grizzly bears for lead contamination. Of 13 bears sampled during hunting season, 46 percent showed elevated blood lead levels, which he defined as 10 micrograms of lead per deciliter.
The 11 bears sampled outside of hunting season didn’t show any signs of lead in their blood.
Lead, considered toxic, typically stays in an animal’s blood stream for about two weeks before it gets deposited in organs and other tissues. Although lead poisoning in human children is rare, it can cause serious health problems, including stomach pain, anemia, lower intelligence and poor school performance.
Seasonal Differences
“There is a pretty substantial difference between hunting season and nonhunting season blood-lead levels [in grizzly bears],” said Rogers. He said he’d need to test more grizzly bear samples to confirm his results.
“It’s pretty preliminary right now,” he said. “It’s just for one season, but as of right now it looks pretty clear.”
In humans, 10 micrograms per deciliter is currently considered an elevated blood level, though some researchers and health professionals have advocated for a threshold of 5 micrograms or even 2 micrograms. A blood lead level of 60 micrograms per deciliter in a human would require medical attention.
The highest level of blood contamination he sampled in a grizzly bear was roughly 28 micrograms per deciliter, Rogers said. “That’s a pretty large chunk of lead they’ve eaten,” he said.
During hunting season, Craighead Beringia South researchers Derek Craighead and Bryan Bedrosian have found blood lead levels as high as 428 micrograms per deciliter in eagles, at which point the animal would likely die as a result of lead poisoning from ingesting lead bullet fragments.
According to Rogers, ingesting lead fragments probably affects grizzly bears differently than birds like ravens and eagles.
“Grizzly bears, they are going to eat huge chunks,” he said. “They don’t really chew per se. The nice thing about the big fragments is that they are more likely to pass through and have a little less surface area to digest.”
As part of his study, Rogers also plans to look for signs of lead contamination in blood and scat samples of black bears, cougars, wolves and coyotes.
“Coyotes probably scavenge the most, then grizzly bears, then black bears, with wolves and cougars at the bottom of the scale,” said Rogers, who said he would use X-rays to look for lead in coyote scat.
Rogers said Craighead Beringia South, the Wyoming Game and Fish Department, Grand Teton National Park, the U.S. Fish and Wildlife Service and the Interagency Grizzly Bear Study Team are helping provide samples for the study.
Questions about consequences
Interagency Grizzly Bear Study Team leader Chuck Schwartz said Rogers’ initial results suggest a link between elevated blood lead levels and hunting season but said more data is needed. Further, Schwartz said he isn’t sure how elevated blood lead levels would affect grizzly bears.
“The real question is, What are the potential consequences?” he said. “In an animal like a bear or a person, it goes through the acid system. Certainly some lead will break down, but most of that lead is going to pass right on through and go out the other end.”
Bedrosian agreed that differences in the digestive system between birds and mammals would likely determine how much ingested lead gets in the blood stream. Physiological differences would also play an important role, he said.
Previous studies have show that lead bullets shatter on impact, spreading fragments throughout the meat. Hunters typically leave the animal’s organs behind when they quarter their kill, sometimes also discarding the blood-shot meat. During hunting season, these offal piles are an important food source for scavengers such as bears, eagles and ravens.
Grizzly bears, ravens and eagles aren’t the only animals that ingest lead bullet fragments. Scientists think this type of lead poisoning has hampered efforts to repopulate the endangered California condor.
And last week, North Dakota health officials recommended that parents refrain from feeding game meat killed with lead bullets to children 6 years and younger because of concerns over lead fragments (see related story on page 8).
Wildlife advocates suggest that hunters switch from lead bullets to copper bullets, which don’t fragment and aren’t as toxic when ingested. Although copper bullets typically cost more, some gun experts say they have greater accuracy and precision than lead bullets.
Link:http://www.jhguide.com/article.php?art_id=3892
“It’s pretty preliminary right now,” he said. “It’s just for one season, but as of right now it looks pretty clear.”
I thought this was an interseting quote. Yes, it's pretty clear that Grizzly lead levels are up, but it doesn't mean it is from lead fragments left in gut piles.
