First came canary in the coal mine. Now there's the lizard on the wall

Researchers have found that wall lizards may be reliable early detectors for toxins and other pollutants from onshore oil drilling activity.

Environmental scientists from the University of Siena in Italy analyzed wall lizards captured at four sites downwind from the Monte Alpi Oil Center in Val d'Agri, an area in Italy's southern Apennine mountains that holds substantial oil reserves.

Tests of the lizards' blood revealed elevations in several chemicals known to cause health problems in both reptiles and humans, including the heavy metals mercury and cadmium. Also present in the animals' blood and bile were signs of exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs)—a family of more than 100 substances generated by the partial burning of oil, gas and other materials.

According to the U.S. Department of Health and Human Services, certain polycyclic aromatic hydrocarbons "may reasonably be expected" to cause cancer in people. They also have been linked to chromosomal changes in children whose mothers were exposed to high levels of these compounds in air pollution while pregnant.

Concentrations of these harmful hydrocarbons were highest near the drilling site, the researchers say.

"Results obtained validate, for the first time, [the Italian wall lizard] as a terrestrial bio-indicator for the assessment of the toxicological impact of onshore extraction activity," the researchers wrote in their paper published online in the journal Science of the Total Environment. "The availability of this reptile in southern Europe, its easiness of capture and lifestyle (insectivorous, resident) as well as the excellent laboratory results obtained for assay of [PAHs], trace elements and enzyme responses to this toxicological stress, make it a perfect terrestrial bio-indicator for oil-derived contamination."

Bio-indicators are plants and animals that scientists use to monitor the presence of toxins in the environment (like the miners' canaries, whose lives depended on an adequate supply of breathable air).

Wall lizards often are a locally abundant species, one trait that "would make them useful as bio-indicators," says biologist Bruce Kingsbury, director of the Center for Reptile and Amphibian Conservation and Management at Indiana University–Purdue University Fort Wayne.

Indeed, Kuwaiti scientists used ants and fringe-toed lizards, a desert species of reptile, to monitor the lingering effects of the well fires at Kuwait's Al-Burgan oil fields during the 1991 Persian Gulf War. According to that study, 12 years after the event, tests of the animals showed signs of contamination with PAHs.

Russell Burke, a biologist at Hoftstra University in Hempstead, N.Y., who has studied Italian wall lizards in the U.S., says the species would be "at least as good as, and possibly better than" other bio-indicators, such as mice and plants. They exist in high densities, are easy to collect, and their organs are easy to reach and analyze in the lab.

One possible drawback, Burke says, is that as insectivores, the lizards are a step removed from direct ingestion of plants, so they might not accumulate environmental pollutants as rapidly as local flora. He says, however, because they are small and easy to keep in captivity—unlike wild mice, which are notoriously difficult to maintain in cages—wall lizards would make a good model species for experiments designed to determine the effects of toxins on mortality, reproduction and growth.