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Environmental Health Perspectn Vol. S3, pp. 143-146.1983 How Are The Physical and Chemical Properties of Chrysotile Asbestos Altered by a 10-Year Residence in Water And up to 5 Days in Simulated Stomach Acid? by Krisna Seshan* Although there have been a number of etudiee on the ingestion of aabeetoe, few studies exist oa bow the chrysotile asbestos itself is altered by the exposure to the acid stomach environment. This study has found that there are changes la the physical, chemical and surface properties of chrysotile asbestos at a result of expoeu-e to water, strong acids, and simulated gastric juices. It was observed that the charge on the surface (the rets potential) is changed from positive to negative; the surface becomes silicalike; and the magnesium is lost from the fibers of asbestos upon exposure to water and acid. It was also noted that the smaller the fiber diameter, the faster the loss of the magnesium. Notable among the changes in physical properties is a change in the refractive index. This means that asbestos exposed to acids or water may not be detectable using the dispersion staining techniques that identify asbestos based on the refractive index. Other physical property changes include the destruction of the gross crystallinity of the fibers. The x-ray diffraction signal disappears when fibers are exposed to acid. However, this study shows that the fibers may still be detected by electron diffraction. It appears that upon acid exposure, the magnesium ions are leached out, leaving a magnesium-free silica network. A positive ion, possibly the proton (H -) or the hydroniurn ion (HjO *), replaces the lost magnesium ion. CO --I o o CO Introduction The prevalence of asbestos in drinking water in the United States has been cataloged (7,2), and the effects of magnesium leaching on the biologi cal effects of inhaled asbestos have been studied (3-5). However, no studies have been found that have considered the effects of magnesium leach ing in ingested asbestos. Several mineralogists (6,7) have studied how asbestos changes under heat and preassure, while others (8$) have studied the surface properties of asbestos fibers. The physical and chemical proper ties of asbestos have been cataloged (10J1). The optical properties of chrysotile have been studied (12), and dye absorption on chrysotile has been Department of Metallurgical Engineering, University of Arixona, TUcaon, AZ 85721. investigated (13,14). The study summarized here attempted to use these various techniques and tests on asbestos fibers altered by exposure to simulated gastric juices and fibers stored in water for long periods of time. Specific details of the studies can be found in the more comprehensive final report, which will be available from the U S. Environmental Protection Agency (U.S. EPA) at a future date. This work impacts two areas. The first is the ares of chrysotile identification in the environ mental matrix. Acid-treated fibers may not be easily detectable by conventional techniques used for asbestos identification. Second, there is the biomedical implication: What changes in fiber properties caused by exposure to water or gastric juice will alter the biological effects of asbestos9 Light and Wei have pointed out the possibility of a connection between surface charge and toxicitv (15). 144 K SESHAN Materials and Methods This project studied the changes in the physi cal, chemical, and surface properties of chrysotile asbestos after exposure to doubly distilled (DD) water for 10 years, 1 N hydrochloric acid for 1/2hr to 5-day intervals, and to simulated gastric juices for up to 5 days. The simulated gastric juices were produced by adding 2 g of NaCl, 3.2 g of pepsin (hog extract), and 7.0 mL of HC1 to a liter of distilled water (76). The pH of the juice was 1.2. Chrysotile asbestos samples were obtained from three sources: International Union Against Cancer (UICC), National Institute of Environ mental Health Sciences (NTEHSi, and Globe, AZ. A variety of tests, including X-ray and electron diffraction, energy-dispersive X-ray analysis, and various surface tests, were performed. The tests may be divided into three main categories: physi-. cal, chemical, and surface charge investigations. Changes in surface charge as a result of acid exposure were determined by the measurement of seta potential (ZP) {17,18) versus pH. Untreated fibers were compared with those treated in 1 N HC1 and those treated in simulated gastric juices. A nitrogen absorption (79) experiment was per formed to determine changes in surface area. Changes in surface were also studied by a dye adsorption method (20). Physical changes to the fiber after acid expo sure were found by measuring the refractive in dex of the fibers. X-ray and electron diffraction were used to study the differences between acidtreated, water-treated, and untreated fibers. Chemical changes to the fiber after acid treat ment were studied by performing atomic absorp tion (AA) analyses of the liquid in which the fibers were treated. The total amount of magne sium lost from the fibers was determined. En ergy-dispersive X-ray analysis on individual fi bers was performed using a scanning transmission electron microscope (STEM). In this case the Mg/Si ratio, as a function of residence time in acid, was determined. Results Upon exposure to simulated gastric juice, the ZP of NIEHS, UICC, and Globe chrysotile asbes tos goes from positive to negative in less than 1 hr (Fig.l). Figure 2 shows the results of asbestos exposure to I N HC1. In 8 hr the ZP still remained positive. The different results suggest that the NaCl and pepsin have an important part to play in changing surface charge. ZP-pH measurements can be used to under stand surface changes. Figures 3 and 4 compare ZP-pH curves for untreated and 0.1 N HC1treated chrysotile. The point at which the ZP curve cuts the x-axis, called the zero point charge (ZPC), has moved from a pH of 6.5 for untreated fibers to a pH of 4 for the treated chrysotile. Since chrysotile has a ZPC of 6 and 6ilica has a ZPC of 4, Figures 3 and 4 show that acid exposure has turned the chrysotile surface to a silicalike sur face. o--c close o----o niehs ukt: 6----------- UICC ffT A P O tF N T iA i Im V l 210L6001S FIGURE 1. Plot showing the variation of leta potential of chrysotile asbestos fibers during an 8-hr treatment in simulated gastric juice. - 0 ------- 1-------`-------1-------1II 0 iJ4 5 TIME in INHCI Incur*) t ' t Figure 2. Plot *howmg the variation of zeia potential of chryaotile aabeatoa from aeveral aources during an 8-hr treatment in 1 N HC1. ZP vs pH EFFECTS OF ACID OS CHRYSOTILE ZP vs pH 145 Figure 3. Plot showing the variation of teu potential vi. pH for chryaotile aabeeioa treated in 0.1 N HC1 for 5 days. The specific conductance of the solution is shown at the bottom, for calibration purposes. Table 1. Surface area of chryaotile asbestos determined using the nitrogen adsorption technique. Sample Glob* (fine' NIEHS (intermediate' Globe (fine' NIEHS (intermediate) Globe (fine) NIEHS (intermediate) TVeatment Untreated Untreated 2 hr. 1 N HC1 2 hr, 1 N HC1 Sonicated Sonicated Surface area. mS/g 29.55 29.76 30.99 59.82 21.21 21.50 Thble 1 shows that the surface area of the treated NIEHS chrysotile is about double that of the untreated chrysotile as measured by the ni trogen adsorption experiment. The chrysotile from Globe was not affected by the acid treat ment. The difference cannot be attributed to larger fibers in the NIEHS material breaking up into smaller fibers with more surface area be cause there was no difference in nitrogen adsorp tion after sonication of both materials. The results of the dye adsorption measurement of surface area are Bhown in Figure 5. The HC1 is shown to have the greatest effect on the asbestos fibers. Figure 4. Plot showing the variation of zeu potential vs pH for chrysotile that has not been treated. One of the important physical properties that changes upon acid treatment of chrysotile is its refractive index. This change for 1 N HC1 and simulated gastric juice treatments is shown in Figure 6. The refractive index decreases from 1.54 for the untreated fiber to 1.44 for the treated fibers. A refractive index of 1.4 is approaching that of the zeolite minerals. This is consistent with the removal of magnesium from the chryso tile, leaving an open framework type of silicate. The result suggests that methods used to identify chrysotile based on its refractive index alone will not be effective in identifying acid-treated fibers Acid treatment also destroys the X-ray diffrac tion pattern of chrysotile. The effect on the X-ray pattern of chrysotile after 3 and 5 days in 1 N HC1 is shown in Figure 7. Crocidolite, an amphibole asbestos form, remains unchanged (Fig. 8). The results of an electron diffraction study of acidtreated chrysotile are shown in Thble 2. It was observed that after 5 days in 1 N HC1, the elec tron diffraction patterns lost clarity; this is as sumed to be related to the loss of magnesium ions from the fiber. 146 K SESHAS Table 2. Chrysodle fibers identifiable by electron diffraction.* Fibers identifiable, ** Source Untreated 30 min. 1 NHC1 3 days. 1 NHCI UICC NIEHS Globe, A2 89 90 92 67 60 80 77 87 80 *At least three layer lines must be visible to be considered identifiable for this test. ST00970I4 Figure 5. Results of surface area measurement using a dye adsorption technique. Chrysotile asbestos from Globe, A2. so i so <0 ro 060 so i sc 60 00* *0 *0 JC -- ze 20 iC J-Oiv 20 0 Figure 7. X-ray diffractometer trace of intensity vs. 2 ft for 1 N HCI-treated chrysotile asbestos. Figure 6. Graph showing the refractive index of Globe chrysotile vs. the time treated in 1 N HC) and in simulated gastric juice, a is the refractive index perpendicular to the fiber axis, y it the index along the fiber axis. Treatment in HC1 cause a and y to become equal and drop to a value of 1.44. Chrysotile asbestos has the formula Mg3[Si205](0H)4. The results of the AA analysis of the liquid in which the asbestos materials had been placed fFig.9) leads to the clear conclusion that acid leaches magnesium from chrysotile fi bers. The excellent agreement with electron mi croprobe results of Monchaux et al. (4) may also be seen in Figure 9. The X-ray microanalysis results shown in Fig ures 10 and 11 show that the smaller the fiber, the greater the magnesium loss. This implies that the loss of magnesium is from the surface of the fiber rather than from the ends. 1 EFFECTS OF ACID ON CHRYSOTILE C DC. D` *<#' 147 ST0097 0 15 Figure 10. Magnesium to silicon ratio vs. fiber diameter for Globe ehrysotile in water and in 0.1 N HC1. ? f' G.' G. 07 " 0< Figure S. X-ray diffractometer trace of intensity v*. 2 8 for 1 N HCl-treated crocidoliu. Jtie v. <K- &ii ----------- Figure 11. Magnesium to silicon ratio vs. fiber diameter for U1CC ehrysotile treated with simulated gastricjuice Figure 9. Percent magnesium as function of time. Compari son with the results of Monehaux et si. (41. Discussion Some of the changes caused by HC1 and gastric acid would make it difficult to identify acidtreated fibers. It will be necessary to develop new techniques for the optimum identification of fi bers after they have been placed in the gstrointestinal tract through ingestion. TOthie- simulated gastric juices used in this study did not contain all components of human stomach ac0id9 .l The complex organic compounds such as muco- and glycoproteins may play a large part in coating the fibers after they are in the stomach and have a great effect on such parameters as surface charge and magnesium leaching. Conclusions Chrysotile asbestos from three sources (UICC, NIEHS, and Globe, Arizona) has been shown to change its physical, chemical and surface proper ties idler exposure to HC1 and simulated gastric juice. The research described in this report was supported by Grant No. CRS0700 from the U.S. Environmental Protection Agency and Grant No. BRSG S07 RR07002 awarded by the Biomedical Research Support Grant Program. Division of 148 K SESHAN Research Resources, International Institute* of Health. The aaaistance of J. Millerte and that of my varioua students is gratefully acknowledged. The research described in this paper has been peer and administratively reviewed by the U.S. Environmental Protec tion Agency and approved for preeentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. REFERENCES 1. Millette, J. R., and McFarren, E. F. EDS of waterborne aabestos fibers in TEM, SEM. and STEM. SEM/1976 9. 451-460(1976). 2. Millette. J. R . Clark, P. J.. Panting, M. F., and TWyman, J. D. Concentration and site of asbestos in water supplies. Environ. HesJth Perspect 34: 13-24 (1980). 3. Wagner, J. C.. Berry, C., end Timbrell, V. Mesotheliomas in rats after inocculation with aabestos and other materi als. Brit. J. Cancer 28. 173-185 (1973). 4. Monchaux, G., Bignon, J., Jaurand, M. C., Lafuna, J.. Sebastian, P., Masse, R., Hirseh, A., and Goni, J., Me sotheliomas in rats following inoculation with acid leached chrysotile asbestos and other mineral fibers. Car cinogenesis 2: 229-236 (1961). 5. 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