A Staff Report from the Straight Dope Science Advisory Board

Do lead fishing sinkers threaten the environment?

November 23, 2004

Dear Straight Dope:

I went fishing for salmon for the first time in my life last year in Washington along a beautiful quiet river with about 100 or so other anglers. Besides depositing beer cans, cigarette butts, fish guts, fast food trash, hundreds of yards of fishing line and multitudes of hooks, etc., I quickly noticed that due the rocky nature of the stream bottom anglers commonly broke their lines several times per session. Most of these "sportsmen" used lead weights on the end their lines. Considering that this has been happening every year for 30 (?) years or so there is probably a truckload of submerged lead lurking there. Does this practice pose a risk to the environment? Is lead really the most suitable material for this endeavor?

Two things you might find surprising: First, lead fishing weights have a long history--the Egyptians used lead net sinkers 5,000-7,000 years ago (reference 2). Second, perhaps the greatest danger posed by lead fishing tackle is neither to fish nor humans, but to birds.

The effect of lead shotgun shot on the environment has been studied for some time. Large die-offs of waterfowl due to lead poisoning were first reported in the late 1800s (reference 5) and continued through the next century, eventually prompting the 1991 Federal ban on the use of lead shot in hunting. However, the impact of lead fishing tackle has not been as well studied, perhaps due to the belief that the enormous amount of lead shot put into the environment by hunters far outweighed any impact from fishing. According to research by the U.S. Fish and Wildlife Service published in the mid-1980s, about 3,000 tons of lead shot were discharged by hunters into the environment annually (reference 4). Reference 2 claims the amount is even larger:

Several million hunters are estimated to deposit more than 6,000 metric tons of Pb shot annually into lakes, marshes, and estuaries; this represents about 6,440 pellets per bird bagged. Shot densities as great as 860,000 pellets/ha (2,124,000/acre) have been estimated in some locations (Wobeser 1981), although concentrations of 34,000 to 140,000/ha are more common (Longcore et al. 1982; Driver and Kendall 1984).

That sounds like a lot, but is it really that much more than the number of lead sinkers entering the environment each year? Determining that figure is a daunting task, as no really good accounting or survey information seems to exist. However, I was astonished to find the EPA noting in 1994 that:

It is estimated that approximately 2,500 metric tons of lead, zinc, and brass sinkers (over 98 percent of the volume represented by lead), an estimated 480 million sinkers, are manufactured each year in the United States (reference 1).

Reference 5 cites a figure of 2,700 tons of lead sinkers made per year in the United States, adding that "400-550 tons" of lead sinkers are made in Canada each year (500 according to reference 7). Unless the number of sports fishers is rising steadily, people are starting large lead sinker collections, or an underground economy of mole people is using them as currency, it's safe to assume that a large portion of these represent replacements for sinkers lost during fishing. If the figures are accurate, we're talking about perhaps 3,000 tons of lead per year entering the waterways of the U.S. and Canada. In other words, an amount not too far from that contributed by lead shot before 1991.

With that much lead entering the water, one would think that there would be many reported cases of large-scale fish die-offs due to lead sinkers. That doesn't seem to be the case, although die-offs due to exposure to other concentrated sources of lead such as mine tailings have been reported (reference 2). The total amount of lead entering the aquatic environment is substantial--in addition to fishing weights and mine tailings, sources of the metal include air pollution, batteries, and lead shot from target ranges. Unlike some other toxins, lead doesn't appear to bioaccumulate in the food chains of freshwater aquatic vertebrates--i.e., you don't find progressively greater amounts of lead as you move up the predator hierarchy due to big fish eating little fish. Such concentration as there is seems to be a function of the age of the organism, with lead concentrating in "hard tissues such as bone and teeth (Eisler 1981, 1984)" (reference 2). The primary biological effects on fish seem to be anemia, depressed blood enzyme levels, growth inhibition in young, and kidney and liver damage (reference 2).

It turns out that the form of wildlife primarily at risk from lead poisoning due to fish sinkers is waterfowl, not fish. This stems from the birds' habit of eating smaller sinkers (especially the "split-shot" type) to use as grit in their gizzards, where they pulverize hard-to-digest items such as seeds. As the sinkers are ground along with sand and rocks, the lead is released into their bodies in concentrated form, leading to debilitation and death. It's estimated that perhaps 2% of all waterfowl die per year as a result of ingesting lead shot and other lead objects. In England, the mute swan suffers greatly from ingestion of lost fishing sinkers--one study in 1982 reported that half of all mute swan deaths in England were a result of lead poisoning. Many varieties of geese, ducks, and cranes as well as non-waterfowl such as the mourning dove and others have been studied and shown to have suffered from lead poisoning due to fishing sinkers as well.

The case of the loon is perhaps the most telling in North America, and responsible for much of the push for legislation banning lead fishing sinkers. According to reference 5:

In New England, poisoning from lead weights and jigs is the greatest source of loon mortality, accounting for 50% of adult deaths (Pokras and Chafel 1992). Likewise, in Canada, 30% of adult loon mortality is due to lead poisoning resulting from sinker ingestion (Scheuhammer and Norris 1996). Ensor et al. (1992) found that 17% of adult loon deaths in Minnesota could be traced to lead poisoning from fishing tackle.

In addition, reference 1 notes:

A 2.5 year study of mortalities of common loons in New England found that lead toxicity from ingested fishing sinkers was the most common cause of death in adult breeding birds ... The study reported that 64 percent of adult common loons (Gavia immer) received for analysis from New Hampshire, and 44 percent of adults received from Maine, had ingested fishing sinkers. Thirty-one adults were examined, and of these, 16 (52 percent) were shown to have died from lead poisoning ... Levels of lead found in the blood of loons that had ingested sinkers averaged 1.4 ppm. The study indicated that scientists consider 0.35 to 0.60 ppm lead in the blood to be indicative of lead poisoning in many species. Levels of lead in the livers of 4 loons that had lead sinkers in their gizzards ranged from 5.03 to 18.0 ppm, while levels in 10 loons that did not have fishing sinkers in their gizzards ranged from <0.05 to 0.11 ppm. The study also states that 5 or 6 ppm in the liver is considered a toxic level in waterbirds. Toxic effects of lead to loons were found to be similar to those seen in other waterbirds.

Sadly, the potential damage to wildlife from environmental lead doesn't end there. Raptors such as the American bald eagle, Andean condor, honey buzzard, king vulture, and California condor can suffer from secondary lead poisoning after eating contaminated fish or waterfowl. Most secondary contamination of predators, it should be said, derives from ingestion of lead shot; many of the lead pellets and pieces from lead sinkers pass harmlessly through the digestive systems of predators or are regurgitated. However, documented cases of poisoning from lead fishing sinkers do exist (reference 1).

Bans on certain types of lead fishing sinkers have been imposed in some areas. New Hampshire has enacted a multi-step ban that will ban all fishing weights of less than one ounce by 2006 (reference 3). New York, Vermont, and Maine ban the sale of lead fishing weights weighing one-half ounce or less (references 9, 10, 11). Canada bans use of lead sinkers weighing less than 50 grams (1.76 ounce), and the UK Environment Agency says, "No fishing weights made of lead may be used except those of 0.06 grams or less and those of more than 28.35 grams" (from 0.002 ounce to 1 ounce). Most U.S. bans affect only the sale of new fishing sinkers, not the use of existing ones. Home manufacture of sinkers is also not prohibited; according to the EPA, "It is estimated that between 0.8 and 1.6 million anglers may produce their own lead sinkers" (reference 1). I never heard of anyone making their own sinkers; it sounds rather boring. But people think handloading is boring too, and it's actually quite enjoyable, so what do I know?

The fact is, lead is harmful to an enormous variety of wildlife, and lead fishing sinkers and other lead tackle contribute significantly to the risk. Sinkers made from an array of alternative materials are available, including copper, bismuth, steel, brass, tungsten, and even densified plastic and ceramic. The chief difference between these and lead sinkers is cost--online fishing gear catalogs suggest that alternative sinkers cost 4 to 8 times as much as lead. Still, reference 7 claims that the annual cost to a Canadian angler should be "less than $2.00." Is that really a big deal to help end heavy metal poisoning? References

  1. USEPA 1994. Lead Fishing Sinkers: Response to Citizens' Petition and Proposed Ban, Proposed Rule. U.S. Environmental Protection Agency, Washington, DC.
  2. Eisler, Ronald, U.S. Fish and Wildlife Service. "Lead Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review." Biological Report 85(1.14), Contaminant Hazard Reviews, April 1988.
  3. New Hampshire Fish and Game Department, www.wildlife.state.nh.us/Fishing/get_the_lead_out.htm.
  4. U.S. Fish and Wildlife Service. 1986. "Migratory bird hunting; availability of a final supplemental environmental impact statement (SEIS) on the use of lead shot for hunting migratory birds in United States." Federal Register 51(124):23443-23447; also US Fish and Wildlife Service. 1987. "Migratory bird hunting; zones in which lead shot will be prohibited for the taking of waterfowl, coots and certain other species in the 1987-88 hunting season." Federal Register 52(139):27352-27368.
  5. Sanborn, Wendy. "Lead Poisoning of North American Wildlife from Lead Shot and Lead Fishing Tackle."
  6. Sidor, Inga F., Pokras, Mark A., Major, Andrew R., Poppenga, Robert H., Taylor, Kate M. Miconia, Rose M. "Mortality of Common Loons in New England, 1987 to 2000." Journal of Wildlife Diseases, Vol. 39, No. 2, pp. 306-315.
  7. Scheuhammer, A.M., Money, S.L., Kirk, D.A., Donaldson, G. "Lead fishing sinkers and jigs in Canada: Review of their use patterns and toxic impacts on wildlife." Occasional Paper Number 108, Canadian Wildlife Service, March 2003.
  8. Scheuhammer, A.M., Norris, S.L. "A review of environmental impacts of lead shotshell ammunition and lead fishing weights in Canada." Occasional Paper Number 88, Canadian Wildlife Service, August 1995.
  9. Vermont Statutes, Sec. 1. 10 V.S.A. § 4606(g) and Sec. 2. 10 V.S.A. § 4614.
  10. Maine Statutes, Title 12: Conservation, Part 13: Inland Fisheries and Wildlife, Subpart 4: Fish and Wildlife, Subchapter 5: Unlawful Fishing Methods, §12663: Unlawful sale of lead sinkers.
  11. State of New York Environmental Conservation Law, Section 11-0308.
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