Volume 13, Number 2, May 1991, pp.13-16
Volume 13, Number 2, May 1991, pp.13-16
There are a number of problems which can arise when cultural property is stored in an environment with airborne pollutants. Leaded coins have been known to deteriorate when stored in highly acidic environments such as those which may develop in oak storage trays or cabinets. Calcareous materials, such as shells, are also susceptible to attack by pollutants. The development of white and gray efflorescence on shells is termed Byne's Disease 1 and has been reported at a number of museums including the Bishop Museum in Honolulu, Hawaii and the Queensland Museum, Bisbane, Australia.
Sometimes the signs of a potentially dangerous atmosphere can be seen on a storage cabinet's hardware. At one museum, the concentration of airborne pollutants was great enough to corrode the internal lock mechanisms of storage cabinets. Although the cabinets were constructed of high quality laminated plywood, the edges (which were not laminated) were exposed inside the cabinets. This resulted in the emission of damaging levels of corrosive volatile compounds, mainly formaldehyde, from the adhesives used in the manufacturing of the plywood. The first indication of the detrimental environment was the corrosion of the locks. This led to a survey of the collection objects in the cabinets. Upon examination, it was apparent that the objects also exhibited problems associated with a corrosive environment, such as the development of white crystalline efflorescence on many Asian metal artifacts.
The sources of formaldehyde in a museum environment may be obvious, such as formalin solutions used in the storage of animal or reptile specimens leaking from improperly sealed vessels, or formaldehyde adhesives used in the manufacture of plywood and particle board. However, it is often difficult to discover whether an environment contains potentially harmful pollutants, identify what the pollutants are, and pinpoint their sources. Therefore, simple qualitative tests such as the "lead coupon" test have been used to obtain a general sense of whether airborne pollutants are present. The conservator simply exposes a clean strip of lead in the suspect environment. At designated times, the strip is visually examined for the development of a gray- white efflorescence. If such surface corrosion occurs on the lead test strip, the curator or conservator is alerted to the potentially damaging environment and can seek mitigation methods. However, such tests are only an indication of the environment in singular locations, and they do not identify the antagonistic pollutant. Due to the increasing awareness of pollutants in the museum environment, the Getty Conservation Institute (GCI) became interested in going beyond this simple pollution indicator test and in finding a way to quantitate levels of formaldehyde and other carbonyl compounds.
In the late 1980s, GCI conducted a survey of airborne carbonyl pollutants at 17 participating institutions from the East Coast to the West Coast, including Hawaii. Nearly six hundred air samples were collected from almost 200 sites within these institutions. This survey provided important baseline pollutant- concentration data for formaldehyde, acetaldehyde, formic acid and acetic acid. This paper will focus on only one of the airborne pollutants detected: formaldehyde.
Levels of formaldehyde detected ranged from less than 0.2 parts per billion (the detection limit of the analytical method) to nearly 800 parts per billion (ppb). However, examination of the distribution of pollutant concentrations revealed that the majority of the sites sampled had concentrations less than 10 ppb. Only 10-15% of the sites sampled had concentrations greater than 50 ppb. Furthermore, the majority of the samples with "high" (>50 ppb) concentrations of formaldehyde were from areas with little air circulation, such as inside display cases and storage cabinets, and all locations with concentrations in excess of 100 ppb were display cases or storage cases. This is not to say, however, that all display cases and storage cabinets had high levels of formaldehyde or other carbonyl pollutants; that would make our task too easy!
From the survey, it was learned that formaldehyde is not ubiquitous. In areas where formaldehyde concentration was high, this could be explained as originating in the types of building materials used, the quality of ventilation, as well as the age of the site. It is well known that new plywood and particle board manufactured with urea-formaldehyde resins, for example, can produce copious quantities of formaldehyde. If the area is not well ventilated, the concentration of formaldehyde builds up. As the material ages, however, the amount of formaldehyde released decreases.
GCI's Environmental Research Program developed a five point strategy for pollutant control:
We have completed the first two objectives for formaldehyde, the third is work in progress, and the final two points are the subject of this paper.
The goal at the outset of the Passive Monitor Project was to identify passive sampling devices (PSDs) which would be used to detect low part per billion levels of pollutants or identify passive samplers whose technology could be stretched to achieve the necessary low limits of detection. In the first phase of the project, the emphasis was on evaluating formaldehyde PSDs developed commercially. Not only is the conservation community concerned about formaldehyde, but it was recently added to the State of California's list of carcinogenic compounds. The interest in detection of formaldehyde in the workplace was advantageous for our project, as there were a number of products on the market for passive detection of this pollutant.
Among the products explored in our study were Sensidyne and National Draeger detector tubes. Detector tubes are pollutant specific. These sorbent tubes are attached to dedicated manual pumps, and a specified number of air strokes are pulled through the tube. In this way, a known volume of air is sampled, and the pollutant concentration can be directly determined based on a color change of the sorbent and the scale on the tube. These formaldehyde detector tubes turned out to not be feasible for use in detecting the low concentrations of formaldehyde seen in the museums; they are designed for measuring much higher levels of formaldehyde. While high ppb levels of formaldehyde in museums could be detected by increasing the number of strokes through the tube, the number of strokes required to detect low concentrations of formaldehyde was impractical.
A number of dosimeter type badges developed in response to OSHA and ASHRAE limits on formaldehyde exposure in the workplace were also tested. Like the detector tubes, these monitors were designed for much higher formaldehyde concentrations than are present in museums. The detection limits of these badges are two orders of magnitude greater than formaldehyde concentration typically found in galleries and storage areas. We have also looked at 3M-brand Formaldehyde Monitor and DuPont's ProTek (TM) badge, both of which were not sensitive enough. Neither Air Quality Research, Inc.'s PF-12 Formaldehyde Monitor nor the Bacharach AirScan (TM) formaldehyde exposure monitors were good candidates for use in museum environments due to reproducibility and exposure requirement problems.
Finally, we tested the GMD 570 Series Formaldehyde Dosimeter badge, and as the initial tests were promising, a Passive Sampling Device validation protocol was developed.
Each potential passive sampler is subjected to the following tests:
Detection limits: Because the intent of the passive sampling device is for use in the museum environment where the concentration of pollutants may be low, it is necessary to insure that a potential passive sampling device (PSD) is effective at the desired level, in the range from 5 ppb to 800 ppb for formaldehyde.
Reproducibility: Reproducibility is confirmed to establish the validity of using a limited number of PSDs (frequently only one) at a particular location.
Percent Recovery: The amount of analyte recovered when the passive sampler is exposed to a known amount of pollutant is also determined. The badge is spiked with a known amount of analyte, and it is confirmed that the analyte is recovered during the analytical process. This is a measure of the analytical method.
Comparison with Active Sampling: The passive sampling device is also compared with a standardized active sampling method to further validate its use.
Interference Studies: The badge's response to the target pollutant in the presence of potential interferences is also studied. Because the museum environment is composed of many different chemical species, interference studies are conducted to assure that there will not be substantial positive or negative interference from other pollutants.
Effects of Low Air Velocity: As noted before, locations with the highest concentrations of pollutants were the sites with little or no air circulation, such as display cases. Hence, the PSD's effectiveness in a sealed case with no air circulation is tested.
Field Tests: Finally, the validated passive monitor is tested in the field at a museum.
The GMD formaldehyde dosimeter badge performed very well in the validation tests completed to date. The detection limit has been determined to be 5.6 ppb hour. This translates to 0.2 ppb for a twenty-four hour exposure. The reproducibility of the badges was found to be 2-5 percent; i.e., the variance among the six GMD badges was only 2-5 percent. The percent recovery was 99%; all of the analyte added to the badge was recovered. When the badges were compared with the active sampling method, the ratio of the amounts of formaldehyde detected was 1.08; in other words, the badges saw 8% more formaldehyde than was detected by active sampling. The difference in the amount of formaldehyde detected in a still-air case when compared to a case with high air circulation was about 20%. While this seems high, the US Environmental Protection Agency allows a 20-30% difference to be a reasonable result when comparing active and passive samplers. The chemistry of the badges is very selective. There were no interferences with typical atmospheric pollutants. Field tests are currently being conducted.
There are a few cautions when using the GMD badges. The badges must be stored in a freezer, and they should be used within 6 months of purchase. This is beyond the date specified by the manufacturer, but they incorporate a large margin of safety. The badges can be exposed 24-48 hours; with any longer exposure periods, one runs the risk of overexposing the dosimeter badge. The badges should be analyzed within one month after exposure. GMD Systems, Inc. does provide economical analysis; however, they can take a month to report the results. Because of this time delay, the exposed badges should be returned for analysis as soon as possible after exposure. Care must be exercised when placing the badges inside a case or cabinet to maintain the integrity of the internal air quality. One cannot leisurely place the badge inside a cabinet or case; in a very short time, there will be complete air exchange and dilution of the internal air with room air. Rather, one must open the case minimally and "slip" the badge into the case or cabinet. Fortunately, the badges are very thin, and this is easily achieved. Thus, a GMD dosimeter badge can be used to determine levels of formaldehyde in museum environments; however, this immediately raises the question: what are safe levels of formaldehyde?
This is a multi-faceted question. Whether or not concentrations of formaldehyde are high enough to precipitate mitigation measures depends on the types of objects stored and their susceptibility to formaldehyde attack. For several decades, carbonyl compounds and organic acids have been recognized in the museum world as corrosive agents for lead objects, leaded bronzes, ethnographic objects, and a variety of other materials 2,3,4,5,6,7. Ideally, there should be no formaldehyde, but this is not a realistic requirement. As a point of reference, the typical concentration in older conventional houses (USA - wood and particle board construction, without urea-formaldehyde foam insulation) is 30 ppb8. While the mean outdoor air concentration of formaldehyde varies with location and weather conditions, in Los Angeles, formaldehyde concentrations in air range from 4-86 ppb9. GCI currently has a research project to determine at what formaldehyde level damage is visible on a variety of organic and inorganic materials. At the completion of this project, acceptable levels can be better specified.
GMD 570 series formaldehyde dosimeter badges are available from GMD Systems, Inc.; Old Route 519; Hendersonville, PA 15339 USA; 412/ 746-3600. The part numbers are 570- 010 for the badges only and 570-050 for badges with prepaid analysis, at a cost of$100 per 10 package and $400 per 10 package, respectively. The badges come with instructions for exposure and storage. There are also explicit analysis instructions for those individuals who have access to an analytical laboratory equipped with a high performance liquid chromatography (HPLC) system.
A few years ago, an East Coast museum purchased a large number of "museum grade" baked-enamel-on-steel cabinets. The staff was very excited about obtaining new storage facilities. As part of standard museum protocol, they placed lead coupons inside the new cases. Much to their horror, the clean lead test strip quickly developed the powdery gray-white surface corrosion product indicative of a damaging environment. The manufacturer was contacted immediately, but they denied responsibility. An industrial hygienist was then hired to quantitate the formaldehyde concentration in the cabinets. In one cabinet, the level was 3 parts per million (ppm). Not only is this level potentially damaging for the objects being stored in the cabinets, but it is 30 times higher than the safe working levels stipulated by OSHA. The manufacturer did finally agree to replace the cabinets' shelves, but not the cabinets. In 1989, GCI visited this museum and tested the internal air quality of the cabinets. At that time, the concentrations were as high as 900 ppb. This was a reduction from previous measurements, but it was still not acceptable.
It was for this situation that the GCI Formaldehyde Eliminator was designed. The Formaldehyde Eliminator uses a special formaldehyde-catalyzed activated charcoal cartridge. The air is pulled through the cartridge. Hence, the Formaldehyde Eliminator is an active mitigation method.
Laboratory validation tests of the Formaldehyde Eliminator have been conducted in a dual chamber experiment. One chamber contained the Formaldehyde Eliminator and the other chamber contained a control Formaldehyde Eliminator in which the cartridge contained inert sand of similar grain size as the activated charcoal in the Formaldehyde Eliminator cartridge. This was important to insure that the air flow through the cartridge was the same in both the control and the experimental eliminators. Both chambers were lined with Teflon in order to minimize formaldehyde absorption on the Plexiglas chambers' walls. Each chamber contained a vial of paraformaldehyde as the formaldehyde source, and the concentration of formaldehyde inside the cases was monitored over the 80-day exposure. The Formaldehyde Eliminator performed very well. The control case had concentrations as high as 1400 ppb (1.4 ppm), while in the case with the Formaldehyde Eliminator, the concentration of formaldehyde was less than the detection limits of 0.2 ppb. The experiment was terminated not because the Formaldehyde Eliminator stopped removing the formaldehyde, but because the source of the formaldehyde was exhausted. In the experimental case, 30 mg of the paraformaldehyde volatiles were effectively removed from the chamber. The Formaldehyde Eliminator is currently being field tested. The design will then be available from GCI.
The Passive Monitor Project and the search for other mitigation technologies continue. GCI plans to identify or develop passive sampling devices for ozone, nitrogen dioxide, hydrogen sulfide and sulfur dioxide within the next year. With the increasing awareness of indoor air quality, many companies are developing passive sampling devices for these pollutants. It is hoped that we will be able to recommend direct-reading passive samplers or samplers that require no special analysis, much like litmus paper for the testing of pH.
1. Byne, L. St.G. (1899): "The Corrosion of Shells in Cabinets;" Journal of Conchology, Vol. 9, No. 6, pp 172- 178, 253-4.
2. Nockert, M. and T. Wadsten (1978): "Storage of Archaeological Textile Finds in Sealed Boxes;" Studies in Conservation, Vol. 23, pp 38-41.
3. Kamath, Y. K., S.B. Hornby and H. D. Weigmann (1985): "Irreversible Chemisorption of Formaldehyde on Cotton Cellulose;" Textile Research Journal, Vol. 55, pp. 663-666.
4. Agnew, N. (1981): "The Corrosion of Egg Shells by Acetic Acid Vapour;" ICCM Bulletin.
5. Tennant, N.H. and T. Baird (1985): "The Deterioration of Mollusca Collections: Identification of Shell Efflorescence;" Studies in Conservation, Volume 30, pp. 73-85.
6. Padfield, T., D. Erhardt and W. Hopwood (1982): "Trouble in Store;" IIC Preprints Science and Technology in the Service of Conservation.
7. Hatchfield, P. and J. Carpenter (1985): "Formaldehyde: How Great a Danger to Museum Collections?;" Center for Conservation and Technical Studies; Harvard University Art Museum.
8. Gammage, RB. and A. R Hawthorne (1985): "Current Status of Measurement Techniques and Concentrations of Formaldehyde in Residences;" Advances in Chemistry Series; Washington, DC; American Chemical Society, Vol. 210, pp. 117- 130.
9. Grosjean, D. and K. Fung (1984): "Hydrocarbons and Carbonyls in Los Angeles Air;"Journal of the Air Pollution Control Association; Vol. 34, No. 5, pp 537-543.
This article is based on a paper of the same title presented at the 1990 WAAC Annual Meeting.
Cecily M. C. Druzik joined the Getty Conservation Institute scientific staff in June 1985. For the last three years, Cecily has been the staff scientist involved with environmental research Dusan C. Stulik is Head of the Analytical Section at the Getty Conservation Institute. His current research is in the application of modern scientific methods in conservation science.
Both authors' address:
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