Lead, Not Mercury

In a recent post, I described how the popularity of loons and the willingness of many folks to pontificate about them without solid data or thoughtful scientific analysis makes loons unique. I tried to point out that this practice can be harmful, if we make misleading statements about loon conservation at a time when some loon populations are declining.

Now, let me give an example. Millions of state and federal dollars have been spent in recent decades in attempting to measure the effect of methylmercury (the toxic form of mercury) on wild animals, especially birds. Without a doubt, more funds have been spent analyzing mercury impacts on loons than on any other aspect of loon biology. What have we learned from this body of work? The major take-homes are that: 1) mercury certainly can affect behavior and survival of adult loons and chicks if it occurs in a high enough concentration in their tissues, 2) high mercury levels tend to occur mainly in loons living on small, acidic lakes, which have negative effects on loons that have nothing to do with mercury, and 3) harmful concentrations of mercury do not occur in most geographic areas within the breeding range. In short, despite an abundance of research and the expenditure of millions of research dollars across three decades, we have no direct evidence that mercury negatively impacts loon populations. In fact, the consensus among loon scientists is that mercury probably has little or no negative impact on most populations.

The situation is dramatically different with lead. Careful analysis of loon carcasses in New England has shown us that lead is quite deadly and affects a great many loons. (The featured photo above shows a deadly lead sinker in the stomach of a loon that died a few days ago in Wisconsin. Photo by Wild Instincts.) In a 2017 study, Grade et al. determined that a whopping 48.6% of the loons they examined had been killed by lead sinkers and lures. The authors estimated that this mortality rate had reduced the New Hampshire loon population by 43%.

The contrast between mercury and lead is stark. Mercury might affect loon survival and breeding success slightly in a few isolated populations. Lead has been shown to cause half of all loon deaths in one state and to make an enormous dent in the loon population of that state.

The contrast between these two toxins goes further. Mercury exposure is pushed to high levels mainly through burning of fossil fuels like coal and oil, which contain mercury. So reducing loons’ exposure to mercury requires a long-term effort to reduce burning of fossil fuels over a large geographic area. In contrast, loons are exposed to lead through our use of lead sinkers and fishing lures. The remedy for lead-related loon deaths is simply to implement use of lead-free fishing tackle in lakes where loons breed. (Steel, tin, and tungsten are common alternatives). Indeed, lead bans are now in place across New England.

Here is the problem. Despite the lack of evidence that mercury affects loons in nature, mercury has become the “go-to” environmental toxin mentioned by many loon researchers. Mercury has become such a prevalent scapegoat in grants, reports, and even published papers that many of us are not keeping its limited impact on loons in proper perspective. A clear-headed, candid, objective review by a loon researcher with a strong background in mercury toxicity would do wonders for loon conservation. At a time when studies have just reported long-term declines in two loon populations, those of us trying to conserve loons would do well to focus our attention on the real enemy.