In major cities marked by industrial pollution, lead continues to haunt the soils well after having disappeared from fuel and paintings. This heavy metal, recognized for its extreme toxicity, remains associated with serious disorders, especially in children. However, at the heart of this persistent contamination, a small Caribbean lizard intrigues researchers. The Anole Brun, now omnipresent in New Orleans, could well change our gaze on the toxicity of lead.
The Anole Brun, a lizard from the Caribbean, settled in the city in the 1990s. Invasive species, it gradually supplanted the local green Anole, better known to the inhabitants. His presence has become so banal that it can be seen on the sidewalks, fences or gardens, without anyone imagining the huge toxic load which he carries in his body.
A study by Tulane University revealed that these reptiles hold the highest blood lead concentrations ever observed in a vertebrate. The researchers measured up to 3,192 micrograms by decilitre in certain individuals, a level that would cause the rapid death of a bird or a mammal exposed in the same way.
Anole Brun supports deadly lead doses for other animals
Scientists expected observing sick, slow or infertile lizards. On the contrary, the tests showed that they were running, climbing and reproducing normally, as if lead had no effect. Researchers have even administered additional doses in the laboratory to measure their tolerance threshold. The results exceeded their expectations. The reptiles only started to show signs of weakness only in concentrations ten times higher than those already noted in the wild.
In their article published in the Environmental Research journal, researchers point out that these performances far exceed those of California condors or Nile crocodiles, two species known for accumulating lead by ingestion. Where these animals collapse, the anoles continue to live without apparent difficulty.
This extreme resistance challenges the scientific community. Donald Smith, a specialist in environmental toxicology at the University of California Santa Cruz, qualified these lead levels as extraordinary and surprising, recalling that beyond 500 micrograms per decilitre, most vertebrates develop severe symptoms or die quickly, as reported by Times-Picayune.
Towards a new understanding of the effects of lead in the living
To explain this paradox, the researchers explore the genetic track. Their analyzes have shown that certain genes related to the transport of metals and the oxygenation of the tissues work differently in these lizards. These adaptations could compensate for the toxic effects of lead on red blood cells and vital organs. The work of the team led by Alex Gunderson, in Tulane, also indicates that the animal manages to kidnap part of the metal in its blood rather than in its sensitive organs, which would limit damage.
The case of the Brown Anole fascinates because it forces researchers to review the toxicity thresholds established for vertebrates. Popular Science underlines that this discovery could open the way for new strategies to combat lead poisoning in other species, including human beings. The animal could thus become a precious biological model to understand how certain organisms neutralize heavy metals.
However, this phenomenon does not remove the always present danger of lead in the environment. In reality, this small reptile could become a useful biological indicator. It would thus allow authorities to more easily assess the risks of human exposure in contaminated areas. The paradox of this little lizard is therefore twofold: surviving in a hostile environment and revealing the invisible magnitude of a poison which, for man, always remains deadly.
