Research Report in support of ASTM D5517 Factors affecting the solubility of metals in art materials

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1 Research Report in support of ASTM D5517 Factors affecting the solubility of metals in art materials Woodhall Stopford Duke University Medical Center Department of Community & Family Medicine Division of Occupational & Environmental Medicine Durham, NC John Turner Angeline Elizabeth Kirby Memorial Health Center Wilkes-Barre, PA September 5, 2017 Introduction Recent studies of mine ore and soils contaminated with lead-containing mine waste suggest that a major determinant of bioavailable lead is the amount of soluble lead presented to the small intestine. Lead ore consists of galena (PbS) altering to anglesite (PbS04) or enclosed in a pyrite or silicate matrix. 1 A further study of the effect of a matrix on solubility has been conducted using a paraffin/stearic acid wax mixed with two levels of a lead chromate-containing pigment to form a crayon. Method ASTM D5517 uses a simple extractant made up of 0.07N HCl. Studies in this report look at additional factors and components of gastric and small intestinal juice that might affect absorption including changes in ph, changes in extractant volume and the effect of sulfhydrylcontaining amino acids, enzymes and organic acids, normally found in gastric and intestinal juices, on metal solubility. Art materials chosen for these studies are a lead-containing pigment and a copper-containing ceramic glaze. Methods All reagents used are reagent grade, conforming to the specifications of the Committee on Analytical Reagents of the American Chemical Society. A crayon wax containing no pigments and containing <1 ppm total lead is used for making lead-containing crayons. A powdered lead chromate pigment containing 60.4% lead is used for making up test crayons. Crayons are formulated as follows: Crayon A Crayon B ppm total lead: The pigment is mixed with molten wax which is then allowed to solidify and ground to a particle size of 0.5 mm, sized with a mesh screen.

2 Weak acid extractions are done in accordance with ASTM D In this method a 100 mg sample is shaken with 5 ml of 0.07 N HCl, the ph is then adjusted to with a 2 N solution of HCl and then is shaken continuously at 37 2 o C for 1 hour. After allowing to sit at 37 o C. for another hour, the mixture is then filtered through a membrane filter with a pore size of 0.45 m and the eluant tested for lead using flame atomic absorption spectrophotometry 3 with a detection limit of 0.02 g/gm of eluant and 5 g/gm of crayon for the entire extraction and analytical procedure. To determine the effect of length of weak acid extraction, this extraction regime is compared with the same protocol except that samples are extracted for 6 hours with continuous shaking prior to filtration. Material remaining on filters after the ASTM D5517 extraction is further extracted with 50 ml of a ph 8.1 buffered aqueous salt solution made up to approximate that found in the jejunum in nonfasting man 4 with the following composition: 6.79 g NaCl/L 0.52 g NaCl/L 1.85 g NaHCO3/L 0.11 g CaCl2/L 1.07 g sodium taurocholate/l After sonication for 5 min. in an ultrasonic bath, the sample is then incubated at 37 o C. for 4 h. while being continuously shaken and then filtered through a membrane filter with a pore size of 0.45 m. The eluant is analyzed for lead as above. To further judge the effect of amino acids on metal extraction, the synthetic intestinal juice is amended with sulfhydryl amino acids found in the small intestine 5,6 : g glutamate/l g histidine/l The extraction procedure with the amino acid amended synthetic intestinal juice is the same as for the unamended juice. In order to determine whether or not the amount of extractant used has any effect on the amount of metal extracted, the lead chromate pigment containing 60.4% lead that is used to make lead-doped crayons, above, and a copper-containing ceramic glaze containing 3.34% total copper are tested using the standard ASTM D5517 method (1:50 art material to extractant by weight) and increasing ratios of material to extractant ranging from 1:200 to 1:315,000. The glaze is formulated with silicaencapsulated copper designed to prevent tarnishing. To further assess the matrix effect of wax, the wax in the crayons is removed with trichloroethane Soxhlet extraction and the remaining pigment analyzed for extractable lead with ASTM D5517. The amount of extractant used in this procedure is based on a 1:50 ratio with the crayon, not the remaining pigment. The extraction results for each sample are calculated in terms of weight of metal extracted per

3 weight of metal in the art material (percent) and ppm of metal that is found in the eluant. Results A 2 hour weak acid extraction of crayon A resulted in extraction of % of available lead in crayon A and % in crayon B (Table 1). Little further lead was extracted with a 6 hour extraction or by using the synthetic intestinal juice extractant, with or without the addition of sulfhydryl amino acids. 7.9% of available lead in the lead chromate pigment was extracted using Method ASTM D5517. When the extractant to pigment ratio is increased, the amount of extracted lead increased until it reached a plateau value of % of available lead at a pigment to extractant ratio of 1:100,000 or greater. The amount of soluble lead in the eluant is 5.3 ppm or less once this plateau is reached (Table 2). When the wax is removed from the crayons, the soluble lead level in the remaining pigment is 84.3% for the pigment from crayon A and 90.5% for the pigment from crayon B (Table 1). The concentration of lead in the eluant for these two extractions was 10.8 ppm for pigment from crayon A and 5.7 ppm for pigment from crayon B. With the copper-containing glaze, extractable copper levels increased as well plateauing at a value of % of available copper once the glaze to extractant ratio reached a value 1:1000. At this level the eluant contained 4.2 ppm copper (Table 3). Discussion A number of experiments were conducted with lead chromate-containing crayons to see if changing the extraction procedure to test whether or not elements that might better represent what occurs in the stomach and intestine would appreciably increase extraction amounts. Increasing the extraction times by a factor of 3 resulted in some increase in the percent extractable lead as did further extraction with synthetic intestinal juice, with or without the addition of sulfhydryl amino acids. The amount of increased extractable lead, however, was near or below the level of detection for the method. When looking at the lead chromate pigment used in these wax crayons, the amount of extractable lead increased with increasing extractant to pigment ratios until a plateau was reached once lead levels in the eluant were 5.3 ppm or less (Figure). Similar findings were seen when a coppercontaining glaze was tested. Extractable copper levels increased until a plateau was reached at a similar value of copper in the eluant (4.2 ppm) to that of lead seen in the pigment study (Figure). These findings suggest that there is an equilibrium between the amount of metal in the extractant and the extractable metal in the material being tested: the greater the concentration of metal ion in the extractant, the less efficient is the extraction. This effect appears to no longer affect the amount of metal ion that can be extracted at metal levels of 5 ppm in the extractant or less. This value is equivalent to extractable metal levels of 250 ppm using Method ASTM D5517 without any further dilution.

4 The maximum level of copper extracted from the silica-encapsulated copper pigment-containing glaze was 13.5%. Neat copper pigments, however, are fully solubilized using Method ASTM D5517. This finding is consistent with decreased lead solubility seen with silica-encapsulation of lead chromate pigments. 7 Removal of the wax in the test crayons and analysis of the remaining pigment resulted soluble lead levels similar to that which would be expected when testing the pigment alone with sufficient volume of extractant that lead in the eluant would be in the range of 5-10 ppm. Wax likely behaves similarly to silica encapsulation of pigments, decreasing the amount available for solubilization. Encapsulation decreases the bioavailability of metals as well. 7 References 1. Ruby MV, Davis A, Link TE, Schoof R, Chaney RL, Freeman GB, Bergstrom P. Development of an in vitro screening test to evaluate the in vivo bioavailability of ingested mine-waste lead. Environ. Sci. Technol. 27: , Standard Test Method for Determining Extractability of Metals from Art Materials, D , Philadelphia, PA: American Society for Testing and Materials. 3. USEPA. Test Method SW-846, 7420 Test Method for lead. 4. Davenport HW. Physiology of the Digestive Tract Fuller MF, Milne A, Harris CI, Reid TMS, Keenan R. Amino acid losses in ileostomy fluid on a protein-free diet. Am. J. Clin. Nutr. 59: 70-3, Hill GL. Ileostomy: Surgery, Physiology, and Management. New York: Grune & Stratton, Pier SM, Gallo MA, Umbreit TH, Connor TH, Gray D, Cappelleri FA. Silica encapsulation reduces bioavailability. Environ. Toxicol. Chem. 10: , Table 1: % Available Lead Extracted from standardized crayons And a lead chromate pigment used in these crayons Sample Pigment (%) Crayon A (%) Crayon B (% ) ASTM D5517 extraction hour weak acid extraction NA Additional lead extracted with synthetic intestinal juice Additional lead extracted with synthetic intestinal juice plus amino acids NA <0.8 <1.6 ASTM D5517 after Soxhlet extraction to remove wax

5 Table 2: Effect of increasing pigment:extractant ratios on percent of available lead extracted from a lead chromate pigment Pigment:extractant ratio Lead extracted (%) Lead in eluant 1: : : : : :100, :170, :200, :315, Table 3: Effect of increasing glaze:extractant ratios on percent available copper extracted from a ceramic glaze Glaze:extractant ratio Copper extracted (%) Copper in eluant (ppm) 1: : : : : :100,

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