By LESLIE BISHOP, guest columnist
The recent tragedy in Flint, Michigan, where people were unknowingly drinking and cooking with lead-laden public water, has reminded us of the dangers of lead in our environment. Lead is clearly a potent and deadly toxin for humans. What is less known to the public is the devastating impact of lead on wildlife.
For all animals, lead that is eaten or inhaled can cause poisoning. Once in the digestive system, lead is then absorbed into the bloodstream. Lead deposited in bone is highly persistent and can be detected years after exposure. At the cellular level, lead interferes with normal biochemical processes.
Although all organ systems can be adversely affected by lead exposure, the nervous system is the most vulnerable. Lethal doses of lead in animals lead to lethargy, digestive failure, blindness, seizures and death. Even non-lethal levels of lead will change the coordination and behavior of animals, reduce immunity to disease, lower reproductive success and chances of survival, and have other long-term effects that result in irreparable damage.
Lead from mining, gasoline and manufacturing is highly regulated by state and federal agencies. And yet, 6,000 to 10,000 tons of lead is dumped annually in the environment by unregulated recreational sporting products: namely, lead ammunition and fishing gear (United States Geological Survey report).
A recent study documented that about 2 billion lead pellets are deposited into the environment worldwide each year by hunting and recreational shooting combined. This lead will take between 100 and 300 years to degrade and disappear, depending on soil conditions and climate.
Wildlife is exposed to lead poisoning from recreational sporting products in two different ways. “Primary exposure” occurs when foraging animals, such as birds, eat lead directly in the form of spent shotgun pellets, fragmented bullets or lead fishing tackle. Lead shot ingestion has been documented in many bird species, including pheasants, wild turkeys, shorebirds, cranes and songbirds.
The dangers of lost lead fishing tackle and weights in lakes are also well documented. The lead sinks to the muddy bottom of the lake, and diving and wading birds mistake the lead for food or grit. For example, biologists have shown that lead poisoning from swallowed fishing tackle is a major cause of death in New England loons. Similar results have been found for other bird species such as brown pelicans, gulls and trumpeter swans, Virtually all species of fish-eating birds, as well as other water-loving animals such as turtles, are at risk of lead poisoning from inadvertent consumption of lost or discarded lead sinkers.
“Secondary exposure” to lead occurs when a scavenger or predator eats an animal already contaminated with lead. Awareness of secondary exposure grew from research on the California condor, a federally endangered species. Condors are obligate scavengers (meaning that they depend on carrion for food) who rely heavily on large mammals like elk and deer. This preference in diet makes the condors especially vulnerable to hunter-killed carcasses and gut piles contaminated with lead. In fact, despite intense management, lead poisoning remains a primary obstacle to the species’s recovery.
Numerous studies on lead poisoning in waterfowl and the subsequent effect on scavenging bald eagles led to a 1991 federal requirement of non-lead ammunition for waterfowl hunting. Despite this positive change, which reduced lead in waterfowl habitats, lead ammunition continues to be routinely used for other types of hunting.
California is the only state that has passed a law, set to take full effect by July 2019, to ban lead ammunition in all types of hunting. Other states have regulations that limit lead ammunition for hunting on specific wildlife refuges, or for hunting specific species like sandhill cranes (for a list, see leadfreehunting.com/state-regulations). Some states have restrictions on lead fishing sinkers. Indiana has no additional regulations other than the federal requirement for waterfowl.
Despite such regulations, scavengers like bald eagles continue to be exposed to debilitating or lethal levels of lead poisoning.
It does not take much lead to make a bald eagle really sick. In fact, a little more than one grain of lead (the size of a piece of rice) is a lethal dose for a bald eagle. For reference, one rifle bullet has 100 to 150 grains, a muzzleloader bullet has 329 grains and a 12-gauge shotgun slug has 421 grains. Therefore, one fired bullet not only kills its target, but can also kill multiple other animals.
Additional studies show negative effects on raptors, such as red-tailed hawks and Swainson’s hawks, that feed their nestlings small mammals contaminated with lead. One lead-contaminated squirrel can kill a hawk nestling and have long-term negative effects on the adult birds.
As one would expect, lead contamination has detrimental effects throughout the food web. Lead fragments are eaten or absorbed by numerous organisms. The breakdown of bullets or fishing sinkers into small fragments also increases the potential for soil and water contamination, which is then absorbed by plants, earthworms and small mammals such as moles, voles and field mice. Studies on water bodies near firing ranges and hunting areas find toxic levels of lead in fish, turtles and frogs.
If so many species are affected by eating lead-tainted animals, it follows that humans, too, are at risk when eating wild game harvested with lead ammunition. While visible lead pieces can be removed during cleaning and preparation, small fragments of lead may remain in the meat. Studies have confirmed this danger. For example, a 2003 study found that hunters who regularly ate birds killed with lead shot had significantly higher average lead levels in the bloodstream than those who did not eat their hunted birds.
The CDC and other health agencies recommend that children and pregnant women should not eat meat killed with lead shot. For children, there is no safe blood lead level, and even slight lead exposure injures the developing brain with lasting effects on cognition and behavior.
The good news is that hunters can choose to use non-lead ammunition and fishers can choose non-lead fishing tackle. Although there has been concern among hunters that the alternative ammunition is not as efficient as lead, several recent studies have shown equal or superior performance in non-lead ammunition.
Historically, the hunting and fishing communities have been leaders in the conservation of nature. Using non-lead fishing and hunting gear is a way to continue this tradition.
By learning about the impacts of lead on wildlife, we have the opportunity to make ethical choices. Some hunting groups are encouraging these choices (see leadfreehunting.com and http://huntingwithnonlead.org/about.html).
Change is always difficult, yet switching to non-lead bullets and fishing tackle makes sense for the health of both wildlife and humans.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She can be reached through the newspaper at [email protected].
