Arsenic Contamination Of Artifacts
A few weeks ago I got to touch the hairy underbelly of an armadillo.
Even though it hadn’t been alive for some time, I was still pretty chuffed about the whole experience—I mean, it’s unlikely I’ll ever have such an intimate moment with an armadillo again.
The beast in question had been briefly removed from its basement cupboard home at the North Carolina Museum of Natural Sciences as part of a behind-the-scenes tour during the recent Science Online conference.
The experience of handling a stuffed armadillo was not just exceptional because it’s a stuffed armadillo. The experience was exceptional because it’s rather unwise to spontaneously handle animal or plant-based artifacts found in museum storage rooms.
Until the 1970s, many biologically-based artifacts were doused with arsenic (as well as lead, mercury and some organic pesticides such as DDT) to keep insect and microbial invaders at bay, explained Lisa Gatens, the NCMNS curator of mammals who let me and others on the tour touch the animal. (For the record, the armadillo was safe.)
Since the practice of adding pesticides to biologically-based artifacts began in the 1800s, there are an awful lot of contaminated museum artifacts out there. And many have levels of arsenic that could pose a problem to human health if handled without protection.
A quick Internet search brought me to Nancy Odegaard, a conservator at the Arizona State Museum, who has spent a huge chunk of her career trying to come up with solutions to this contamination problem.
Odegaard told me that concerns about contaminated artifacts initially arose in the 70s and 80s, during that era’s increasing awareness about the dark side of some commonly used chemicals. The museum community began to worry that conservators and curators working with artifacts might be at risk, not to mention museum goers participating in hands-on exhibits.
Then in 1990, the US government launched the Native American Graves Protection and Repatriation Act.
At this point, museums began returning artifacts to Native Americans who might start using the pieces in ceremonies instead of storing them behind glass.
Since many of these artifacts were made of leather, feathers and other biologically-sourced materials, they too had been subject to toxic anti-pest measures.
The potential health risk to Native Americans was very concerning. “I lost sleep thinking about this,” Odegaard says. “In particular, you worry about head-dresses, which are worn near the eyes, nose and mouth–this is ground zero for contamination entry.”
Odegaard started organizing seminars and conferences with Native American leaders, conservators and medical researchers to discuss contamination and how to assess health risks. (She is an author on this 2000 JAMA letter entitled Arsenic Contamination of Museum Artifacts Repatriated to a Native American Tribe, as well as a sequence of other publications on the topic.)
The question is: What can be done to decontaminate the artifacts?
The easiest thing would be to soak the pieces in water or another solvent to extract the poison, and then dispose the bath water safely. You might add a chelator, something that nabs and sequesters metals such as arsenic, lead or mercury. Odegaard and others have thought about using lipoic acid, which is produced in our own body for removing toxic chemicals.
But many artifacts made of feathers, textile and leather are too delicate to handle any kind of bathing, or they contain dyes that could leach out.
So conservators have started investigating gentle vacuuming as an alternative as well as higher-tech solutions such as supercritical carbon dioxide. Under pressure, CO2 goes into a so-called “supercritical” liquid state, where it can penetrate into nooks and crannies like a gas but dissolve like a liquid.
Supercritical CO2 extraction is currently used by the food industry to remove caffeine and hops, but the technique is also promising for getting rid of harmful contaminants from feathers, textile, and leather artifacts, Odergaard said. The downside is supercritical CO2 sometimes does its job too well, by removing more than just the poison.
(Say you have a leather artifact that has contaminants but also has candle wax because it was hung in a church or dirt because it was involved in an important battle. Conservators would want to keep the wax and dirt because it’s part of that object’s “provenance” or life-history, but obviously they’d like to lose the toxic components. Unfortunately supercritical CO2 gets rid of everything.)
Although there are some cleaning options, the majority of contaminated biological specimens in museum stores remain as is. Conservators take precautions when handling them by wearing masks and gloves while curators make sure the objects are sequestered behind glass when displayed to protect the health of museum goers.
And now that combating vermin with chemical pesticides is verboten, museum staff have developed other measures to keep biologically-based artifacts safe.
If objects are being attacked by pests, the artifacts are now typically frozen and/or put in an oxygen-free environment to kill any invaders, Odegaard said. These alternatives are neither as potent nor as long-lasting as the arsenic, but they are infinitely safer.