Assessing the Impact of Sanitizing Products on Collection Items

This is a guest post by Cindy Connelly Ryan, a Preservation Science Specialist in the Preservation Research and Testing Division. Her research interests include the light sensitivity of inks, dyes and organic colorants, deterioration and stabilization of verdigris and iron gall ink, and historic recipes and working methods for artists’ materials.

Over the ever-lengthening months of the COVID-19 pandemic, routine use of hand sanitizer and disinfectant wipes or sprays has become commonplace in our daily lives; at the grocery store, at the park and playground, and everywhere else we go. Such uses are included in the Library’s guidance for employees returning to work on site, in the CDC’s regularly updated guidelines for preventive measures, and N-list of tested effective sanitizing products.

Across the country public libraries, research libraries, archives, records offices, and other cultural institutions are now slowly re-opening their doors to researchers –indeed, four LC reading rooms are welcoming the first researchers in over a year as I write this today. In planning for re-opening, questions have arisen about the potential risk of transmitting viruses via shared handling of collection items – and perhaps less obviously, what effects might these now-ubiquitous sanitizing products have on the collection items themselves, if transferred from users’ hands and desks? The first question has been explored in depth by the REALM project, a joint initiative of OCLC, the Institute of Museum and Library Services, and Battelle Labs, with support from many partner organizations, including the Library of Congress. To explore the second question, the Preservation Research and Testing Division has examined some common sanitizers’ impact on eight materials representative of a cross-section of the Library’s general and special collections, including book cloth, parchment, leather, and five types of paper including glossy coated magazine paper, newsprint, sized rag, and copy/printer paper.

We started by reading labels – never a bad idea – and confirmed that the wipes and hand sanitizer currently distributed for staff use at the Library are typical in their composition compared to the dozens of similar commercial products we surveyed, namely a water-based wipe with quaternary ammonium compounds (QAC’s) and an alcohol-based gel. Rather than attempt a wide survey of constantly-changing consumer products, we focused on the ones in use at the Library, as both immediately relevant to our collection and representative of their classes. We added a simple 70% alcohol-30% water spray as recommended by the CDC, and looked at the impact on our selected materials from different scenarios of use. These comprised direct application to the material (which could be deliberate or as an accidental drip), finger transfer of sanitizer gel after a 15-second drying period, and finger transfer after the users’ best judgement that their hands were dry. For comparison, we included touching the materials with freshly washed hands, which remains the CDC’s top recommendation for reducing virus transmission, and one un-touched sample of each material.  Samples were examined shortly after application, and at intervals during accelerated oven aging at mild conditions to simulate the passage of time.

At the start of this project, our Division was still working almost completely remotely. Some early home-workshop exploration of the LC sanitizers and an assortment of readily available commercial products applied to laboratory filter paper showed that pure water and alcohols evaporated, but all the others left residues that fluoresce readily under ultraviolet light.

As the project progressed, spectral imaging of our full set of samples after accelerated aging confirmed this deposition of fluorescing residues for the direct application of gel and wipes on all but one test material, the gelatin-sized cotton rag paper.  Additionally, we saw visual evidence of surface coatings being disturbed by the alcohols (for example, on the bookcloth), cockling (wrinkling) of the moisture-sensitive newsprint and parchment in the application area, and some cases of ‘tidelines’ forming on older papers from the water or alcohol moving degradation products of the paper as they evaporated.  Thus, direct applications of any of these sanitizers to collection items is definitely not recommended.

A prior study conducted in 2011, inspired by the H1N1 bird flu outbreak, found that all the hand sanitizers we tested at that time discolored notably after a period of aging at standard ASTM conditions when applied as an even film on paper.  In our current, more realistic application and milder aging conditions, reflectance spectroscopy again shows discoloration developing on our substrate materials during aging for the wipe, for direct application of the gel, and to a lesser extent for the finger transfers.  The QAC wipe caused the most marked color change, with yellowing already visible to the eye on some materials after the first aging interval. These color changes, broadly speaking, correlate to when fluorescence is noted in the imaging data; some of our materials altered from the aging itself, making close comparisons of fluorescence and color change difficult for parchment and newsprint in particular. Across all the materials, there is less evidence of either discoloration or fluorescence for the finger transfers than the heavier applications, particularly the ‘best practice’ drying period, which only appeared to affect the coated lithography paper.

A more sensitive laboratory test, thermal desorption gas chromatography-mass spectrometry, detects the main marker compounds of the hand sanitizer for all of the finger transfer scenarios. This indicates that potentially discoloring materials do indeed transfer even in the ‘best practice’ scenario.

Ultimately, our results echo the recommendations of the CDC – and your grandmother – that the best advice is to wash your hands often. Freshly-washed hands induced the least evidence after aging of any fluorescing residues (only a faint trace on the filter paper), and negligible color changes on the order of noise for all but the aging-sensitive materials and a small effect on the coated paper.

Based on our admittedly limited results, the use of hand sanitizers before handling library collection materials does introduce a measurable risk of transferring residues that fluoresce and, in several cases, are seen to discolor with aging.  If hand sanitizers are used, thorough drying is recommended before handling collection items to minimize transfer. For sanitizing surfaces, simple alcohol-water sprays carry less risk to library collection materials than products containing QAC’s, since alcohol-water sprays evaporate without leaving residues, and again, thorough drying is recommended. Cleaning and sanitizing products should not be applied directly to paper, parchment, or bound books.