Some lead bullets fired from high-powered rifles scatter lead fragments much farther into deer than hunters might assume, according to a Department of Natural Resources study released Tuesday.
That means the state's venison processors and 500,000 deer hunters must trim much farther from wound channels to avoid lead contamination.
Lead was found up to 18 inches from wound channels in a study on sheep conducted by the DNR in July, said Lou Cornicelli, DNR big game program leader. The sheep, euthanized first, are anatomically similar to white-tailed deer.
"Some high-velocity lead bullets break apart almost instantly, throwing small pieces of metal all over the place,'' Cornicelli said.
Routine trimming likely will not remove all fragments, and the agency can't make a recommendation about how far out from the wound to trim. The fragments generally are too small to see, feel or detect while chewing.
The study also found rinsing a carcass tended to reduce lead near the wound channel by about 20 percent, but also spread lead.
Cutting 2 inches around the wound channel removes only about 30 percent of the lead fragments, Cornicelli said.
Ballistic-tip bullets, made to rapidly expand on impact, fragmented the most. They averaged 141 fragments per carcass, with an average maximum distance of 11 inches from the wound channel.
Soft-point bullets and bonded lead-core bullets with exposed lead cores had an average of 86 and 82 fragments, respectively, also with a maximum distance of 11 inches.
Shotgun slugs and muzzleloader bullets fragmented far less than lead bullets fired by high-powered rifles. Still, shotgun slugs left an average of 28 fragments at an average maximum distance of 5 inches from the wound. About 25 percent of the state's firearm harvest falls to shotgun slugs.
Bullets with no exposed lead (with copper cases completely surrounding lead cores) or all-copper bullets would "significantly reduce or eliminate lead exposure.''
The study was prompted by discovery last spring of lead fragments in venison donated by hunters to food shelves in Minnesota, North Dakota and Wisconsin. In Minnesota, venison was pulled from food shelves, and changes are being made to the program this fall to reduce lead contamination.
Despite the changes, state officials recommend that children under 6 and pregnant women not eat venison donated to food shelves. Exposure to lead can be harmful, particularly to children, and may not always produce visible symptoms, officials said.
The $50,000 study was paid for with venison donation program dollars.
Several types of bullets were shot from different firearms into 72 dead sheep in July. X-rays and other equipment were used to examine for bullet fragmentation.
DNR officials said hunters will have to decide how to react to the study.
"Our hunters are smart,'' Cornicelli said. "They will be able to measure what they need to do.''
Among the DNR tips:
• Nothing in the study suggest people shouldn't go deer hunting, but should take lead exposure seriously.
• Don't use deer with excessive shot damage.
• Bullet selection, firearm type and shot placement can affect lead exposure. Try for cleaner and closer shots.
•Trim liberally around the wound channel.
Study results and an online DNR presentation are at www.dnr.state.mn.us/hunting/lead.