Aqueous alpha-lipoic acid solutions for removal of arsenic and mercury from materials used for museum artifacts

Recorded use of pesticides in the conservation of artifacts dates back to the 16th century. Museums today are faced with a tremendous task of identification and remediation of pesticides from artifacts in order to protect museum workers and the general public. In addition, artifacts are being repatriated by Native American tribes for use in cultural ceremonies which may subject the practitioner to health risks. Arsenic and mercury salts are among the pesticides that were used that are highly persistent and toxic. The primary challenge lies in removing these hazardous and persistent metals without damaging the materials or pigments on the objects.; Concentrated aqueous alpha-lipoic acid solutions were developed for removing arsenic and mercury pesticides from materials commonly used in museum artifacts. The alpha-lipoic acid solutions were reduced using natural sunlight or laboratory ultraviolet lamps to enhance the binding of arsenic. The solubility of alpha-lipoic acid in various organic and inorganic solutions was determined and environmental parameters that impact the reduction and solubility, such as pH and temperature, were examined. The kinetics of the reaction of arsenic (III) with reduced lipoic acid was examined by varying the reduced lipoic acid, base and arsenic concentration as well as temperature and stirring conditions. The results indicated that the reaction occurs at a moderate rate primarily within 8 seconds in air. The reaction is chemically rate limited enhanced at higher temperatures and lower pH. Aerobic conditions significantly decreased the extent of the reaction with increased 17 stirring rate. This impact was minimized by using a nitrogen environment or by limiting agitation during the reaction step.; The sorption and desorption kinetics of arsenic (III) and mercury on natural materials such as cotton, wool, paper and feathers were studied using a Niton handheld X-ray Fluorescence Spectrometer (XRF) to monitor contamination levels before and after treatment. Sorption occurs by both physisorption (which renders a large fraction of the contamination easily removable) and by chemisorption. Stirring and increased temperature enhanced the removal of metals from cotton and wool indicating a diffusion led control mechanism in the desorption process.; The methods developed were capable of removing up to 1000 Rmug/cm 2 arsenic (of sodium arsenite) from simulated artifacts to levels near the lower detection limit of the XRF (1 mug/cm2) without leaving detectable residues according to Attenuated Total - Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR). Similar results were achieved in removing mercury (of mercuric chloride) from cotton and paper; however, the solutions and processes developed were not capable of removing mercury from sulfurbearing materials such as wool and feathers.; The aqueous lipoic acid solutions and processing sequences developed have potential for utilization by conservators as the techniques do not require expensive equipment and can be used by museums with minimal training.