Volume 18, Number 1 .... January 1996

The Merckoquant 10026 Arsenic Test for Natural History Collections

Historical Background

In the early part of the twentieth century, lead arsenate powder was used in museums to prepare organic materials such as furs, leathers, and plant materials for exhibition. The arsenic powder acted as an insecticide and prevented the artifacts from being damaged by insect infestation. The treatment of artifacts with lead arsenate was originally used by taxidermists as a preservative and insecticide. The use of lead arsenate was discontinued during the 1930's by most of the taxidermy profession due to health concerns. Arsenic, a transition metal, is no longer used as an insecticide due to a greater awareness of its toxicity.

Many taxidermists now use previously tanned skins in their work. These skins have been tanned using chemistry that does not pose a health threat, if used properly, to the user. The preservative, formaldehyde, is often used in the contemporary preservation of furs and leathers. Many of the artifacts that were previously treated, however, still retain varying amounts of arsenic dust on their surfaces. A powerful and very effective insecticide, many of these artifacts remain in excellent condition and have resisted any type of insect damage over the years.

Since arsenic is very toxic, handling artifacts that have been treated with the powder requires a different protocol. The handler must be aware that the artifact has been treated with a toxic substance and must handle the object and treat it as such to avoid health risks. Artifacts made of fur and skin that remain in excellent condition over many years are suspect and an arsenic test* should be performed to confirm the presence or absence of the toxic powder.

Laboratory Procedure

Twenty-five milliliters of deionized water are placed in an Erlenmeyer flask. Five swabs are prepared in the following manner: each is dampened with deionized water and rolled over a different part of the artifact to pick up any arsenic powder residue. All swabs are then placed in the flask where they are allowed to soak for thirty minutes.

While the swabs are soaking, an indicator strip is prepared by inserting it through a slit in a graduated test tube cap. After thirty minutes has elapsed, five milliliters of the solution is transferred to the graduated test tube and Reagent #1, Zinc powder (Zn), is added. After shaking and thoroughly mixing the solution with the powder, Reagent #2, 32% Hydrochloric acid (HCL), is added to the solution. The test tube is then capped with the cap holding the indicator strip.

Reaction Mechanism

The addition of Reagents #1 and #2, Zinc powder and Hydrochloric acid respectively, to the solution causes a reaction between the two reagents. In this reaction, Hydrogen gas is generated(H₂.) This gas reacts with any arsenic that is present within the test tube to form Arsine gas (AsH₃.) The arsine gas turns the reaction zone on the tip of the indicator stick, which contains Mercury (II) Bromide, yellow to brown depending on the concentration of arsenic. The varying discolouration of the reaction zone is due the formation of mixed arsenic mercury halogenides (AsHgBr₂).**

Treatment

If an artifact is positive for arsenic, partial removal can be accomplished through vacuuming the artifact. Before the procedure commences, however, a special area in the lab is cleared and gloves and swabbing material are prepared. These items are disposed of properly, with the aid of an environmental waste disposal company. At the termination of the procedure, the area is thoroughly cleaned.

The vacuum used in the procedure is a Nilfisk Quad-Filter Vacuum Cleaner. The four filters within the Nilfisk are as follows: a paper bag; a napped cotton filter; a napped cotton sock over the motor; and a High Efficiency Particulate Accumulation (HEPA) filter which filters 99.97% of the incoming particulates down to 0.3 microns. All residues recovered from the artifact are disposed of with the aid of an environmental waste disposal company. A Steri-Dent Dental Vacuum which would normally be used in vacuuming an artifact would not be proper because of an internal water trap that traps the surface particulates that are lifted from the artifact. The water in the trap would create a toxic waste that would have to be handled by an environmental waste disposal company and having the waste in solid form within a filtering system is much easier to accomodate. The toxic waste potentially formed in the water trap differs from any arsenic in the graduated test tube which reacts with the hydrogen gas to form arsine gas. This gas is filtered through the fume hood.

Conclusion

It should be stressed that vacuuming an artifact will not necessarily remove all of the contaminant, arsenic. The arsenic test simply establishes a different protocol when handling the artifact to avoid health risks.

*The Merckoquant 10026 Arsenic test can be obtained through the following addresses:

Thomas Scientific, P.O. Box 99, Swedesboro, New Jersey 08085-6099, Tel.: 1-800-345-2100. Catalog No. 3108-L55 or

E. Merck, Postfach 4119, D-6100 Darmstadt 1, Federal Republic of Germany, Tel. (06151) 72-0, Tlx. 4 19 32-0 em d.

**The reaction mechanism is as follows:

1. Zn+ + H+CL- (yields) Zn₂+ + H₂ (hydrogen gas emission)
2. As₃+ + 3H₂ (yields) 2AsH₃ (arsine gas formation)
3. AsH₃ + 3HgBr₂ (yields) As(HgBr)₃ + HBr (arsenic mercury halogenides)

Bibliography

Jim Carpenter, "Museums Can Be Hazardous to Your Health," Aviso 6 (June 1985), 1-2.

Feigl, F. "Spot Tests for Inorganic Analysis." Elsevier Publishing Co.: Amsterdam, 1972.

C.A. Hawks and S.L. Williams, "Arsenic in Natural History Collections," Leather Conservation News 2/2 (Spring 1986), 1-4.

D. Muir, M. Lovell and C.P. Peace. "Health Hazards in Natural History Museum Work," The Museums Association (1981), This article may be obtained through the following address: The Museums Assn, 34 Bloomsbury Way, London WCIA 2SF.

James Swope, "Arsenic in Taxidermy Specimens," Conservation News 1/4 (1984), p.1.