Tiny lizards in New Orleans are packing the highest levels of lead any vertebrate on the planet\u2014and it doesn\u2019t seem to phase them in the least. <\/p>\n
The new record comes from a study recently published in the journal Environmental Research that measured the volume and impact of lead<\/a> on brown anoles (Anolis sagrei) from two different city neighborhoods. \u00a0\u201cWe were shocked by the data, then it just kind of snowballed from there,\u201d says Annelise Blanchette<\/a>, who worked on the study as a Ph.D. student at Tulane University in New Orleans. \u201cThe fact that they are thriving is unique to [these lizards].\u201d<\/p>\n Monitoring anoles that carry such \u201cunprecedented\u201d levels of this heavy metal could help public health officials identify city neighborhoods with higher potential human health risks. \u201cAnimals really are these sentinels that show what is there in the environment,\u201d says Jesse Berman, an environmental epidemiologist at the University of Minnesota who was not involved in the work.<\/p>\n How lizards pick up lead<\/p>\n Previous research<\/a> from Tulane linked lead tolerance with aggression in mockingbirds around New Orleans, and Blanchette wanted to expand on this. \u201cWe have a decent understanding of how heavy metals affect humans but a less well-rounded understanding of how it affects wildlife,\u201d she says.<\/p>\n (Why do most U.S. eagles have lead poisoning?<\/a>)<\/p>\n So Blanchette and her colleagues collected brown anoles from an older urban area uptown near Tulane University and another in Lake Shore, a more suburban area by Lake Pontchartrain. In the lab, the researchers found extremely high lead levels in the lizards\u2019 blood. One individual had 3,192 micrograms of lead per deciliter of blood. \u201cI remembered getting that data back and being very surprised that it was alive,\u201d Blanchette says. The lizard average was 955 micrograms per deciliter\u2014still extremely high compared to results from other vertebrates, including humans.<\/p>\n \u201cIf you were anywhere near 10 micrograms [per deciliter], doctors would be concerned,\u201d says Blanchette, now a biologist at the U.S. Environmental Protection Agency. \u00a0Levels that these lizards could tolerate would definitely be fatal for humans.<\/p>\n The lizards in the uptown area had higher levels on average than those from the suburbs. Blanchette says this is likely due to a couple of factors. For one, the Tulane area is a little older, meaning the houses are more likely to still have lead paint. Conversely, Lake Shore has younger buildings and less lead paint, but Blanchette also notes that its yards and other green spaces have a lot more remediated soil brought in from places with less lead contamination.<\/p>\n In neighborhoods, paint is a big source of lead. It erodes over time, and tropical storms can also knock flecks off the walls of houses into the surrounding soil. Brown anoles then ingest lead through direct contact with paint on houses or contaminated soil or by eating small arthropods.<\/p>\n Blanchette says that industry along the Mississippi is also likely responsible in part\u2014it\u2019s not just paint from old houses. The city \u201cis unfortunately a hot spot for a lot of potential avenues for contamination, but it\u2019s not a problem unique to New Orleans,\u201d she says, adding that older cities likely have similarly high levels of lead contamination in the soil.<\/p>\n Yet, even the more contaminated uptown lizards didn\u2019t seem affected by the lead in tests of balance, endurance, and sprint speed. They didn\u2019t find any significant physical differences between lizards with higher lead levels and those with lower levels.<\/p>\n (Heavy metals give these spiders a powerful bite<\/a>.)<\/p>\n Testing lizards\u2019 lead limits<\/p>\n To determine how much lead these lizards can ingest safely, the team dosed Lake Shore lizards for 60 days at levels ranging from no lead to 500 milligrams of lead per kilogram of body weight per day. The highest two levels were too much for the lizards. \u201cThey had ulcers that developed around their mouths, and they had stopped eating,\u201d Blanchette says.<\/p>\n But those receiving daily doses between one and 10 milligrams of lead per kilogram of body weight had no discernable symptoms. At the end of the test period, one lizard from the 10 milligrams per day group had a blood level of 10,600 micrograms per deciliter. \u201cThat was the highest that we could confidently say we aren\u2019t seeing any negative effects,\u201d Blanchette says.<\/p>\n Measuring only balance, speed and endurance may not be enough to definitively say these lizards can tolerate high lead exposure. Helle Bernstorf Hydesov<\/a>, a wildlife veterinarian at the University of Copenhagen who has studied lead<\/a> in mammals but was not involved in this recent research, says there is \u201cno such thing as safe lead exposure\u201d and questions whether it\u2019s worth talking about tolerance. \u201cYou can kind of say, that if you\u2019re not finding any side effects to lead, it\u2019s because you haven’t investigated the right health parameters,\u201d she says.<\/p>\n For now, the numbers Blanchette\u2019s team found in the lab and in the wild put anoles in a league of their own. Marc Humphries<\/a>, an analytical chemist at the University of the Witwatersrand in Johannesburg found 1,310 micrograms of lead per deciliter in one Nile crocodile<\/a> in in South Africa\u2014previously the highest ever recorded in a free-ranging vertebrate.<\/p>\n \u201cReptiles appear to possess a remarkable capacity to tolerate high levels of contaminant exposure with minimal apparent physiological effects,\u201d Humphries says. In both the crocodile and lizard cases, \u201cthese lead concentrations would be lethal to any mammal or bird, but reptiles somehow manage to survive.\u201d<\/p>\n