Study Shows Lead from Bullet Fragments in Venison can be Absorbed into Bloodstream, Cause Risk of Lead Exposure
27 April 2009
New research shows that people are risking exposure to lead by eating venison from game animals that were killed with traditional lead-based rifle bullets and processed under normal procedures, according to a joint study by The Peregrine Fund, Washington State University, and Boise State University.
The peer-reviewed study was published online today by the Public Library of Science journal PLoS One and is available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0005330
"We interpret the absorption of lead into the bloodstream of our test animals as clear evidence that humans can absorb lead from ingested bullet fragments," said Grainger Hunt, lead author of the study.
This research challenges recent claims by the sport-shooting industry that lead in venison harvested with traditional ammunition poses no health risk to people who consume game meat. Primary prevention by harvesting game animals with lead-free alternatives to lead bullets is the most certain way to avoid lead exposure, Hunt said.
The dangers of lead to human health have been known since Roman times, but research in the last 10 years has shown that blood lead levels formerly regarded as trivial can have debilitating and often irreversible effects. Among these are intellectual and behavioral damage in children, including fetuses exposed before birth. Effects on older people include impaired motor function, kidney disease, cancer, and heart disease.
More than a decade of work by The Peregrine Fund in Arizona to recover the endangered California Condor revealed that lead residue from bullets used to hunt game is the most frequent cause of death in wild condors. When Peregrine Fund researchers saw hundreds of lead fragments in x-rays of rifle-killed deer they wondered if people eating venison might be consuming lead as well.
In the current study, they used x-rays to look for lead bullet fragments in packaged venison from 30 deer shot with traditional lead bullets. Each deer had been taken to a different commercial meat processor. To simulate human consumption of the venison, the researchers then fed samples of the processed meat to test animals and monitored subsequent changes in blood lead concentration. Pigs were used as human surrogates for these experiments because of biological similarities to the human digestive tract.
Four pigs were fed venison that had tested positive for bullet fragments, and four received venison without fragments from the same deer. Average blood lead concentrations in pigs that consumed meat with bullet fragments peaked at 2.3 micrograms per deciliter just two days after the meal. That was significantly higher than the pigs that ate fragment-free venison, whose blood lead levels averaged 0.6 micrograms per deciliter.
Lead is mistaken by the human body for calcium and replaces it in nerve tissue, organs, and eventually in bone. During pregnancy, lead stored in bone may be released along with calcium, thereby exposing fetuses. Release of bone lead may again occur late in life, and evidence now suggests that this toxic material may be associated with cognitive difficulties among the elderly.
Since 1991, the Centers for Disease Control has required medical intervention for children whose blood lead levels exceed 10 micrograms per deciliter. However, recent studies associate as little as 2 micrograms per deciliter with impaired cognitive function in children, as well as increased risk of cardiovascular problems in adults. In 2005 the CDC acknowledged that there is no "safe" lower threshold level for blood lead in young children and stressed the importance of preventing childhood exposures to lead. The CDC's 1991 benchmark is out of date, according to toxicologists who proposed a new benchmark of 2 micrograms per deciliter in 2006.
"It is conceivable that deer-hunting families attain higher lead levels with frequent consumption of venison," Hunt said. "Lead bullet fragments were patchily distributed in the meat, so a person eating a single venison burger may or may not get a dose – it's a game of Russian Roulette. The more often they eat venison the higher the odds they will be exposed to lead."
Ammunition lead has been found at elevated levels in the blood of subsistence hunters and their families in Greenland and Canada where game meat is a regular part of the diet, and a 2008 CDC study in North Dakota found average blood lead concentrations of game consumers were statistically higher than a comparison group that did not eat game meat.
Of particular concern are the frequent beneficiaries of food donations, many of whom are already at risk from lead paint exposure in older low-income housing.
Several state Health Departments have recommended that children under 6 years old and women of child-bearing age should not eat venison killed with lead bullets, and urge all consumers to take precautions. A list of lead-free ammunition is available on the web at: http://www.azgfd.com/pdfs/w_c/condors/Non-LeadAmmo.pdf