Ingestion Of Asbestos Research Articles

Evaluation of potential gastrointestinal carcinogenicity associated with the ingestion of asbestos.

The inhalation of asbestos, depending on the fiber type and dose, may be associated with the development of mesothelioma and other asbestos-related diseases. However, little is known about the potential adverse effects associated with the ingestion of asbestos. Evidence of asbestos fibers released from asbestos-cement pipes used in water distribution systems has led to concerns of potentially contaminated drinking water. The purpose of this study is to determine whether ingestion of asbestos fibers may lead to cancerous effects on the gastrointestinal (GI) tract. Data from animal and human studies were analyzed using a weight-of-evidence approach to evaluate the potential risk of GI cancers associated with asbestos ingestion. Seventeen human and 23 animal studies were identified and evaluated in this study. Animal studies were conducted in multiple species with inconsistent dosing protocols. Overall, animal studies reported that the asbestos fibers, irrespective of fiber type and dose, failed to produce any definitive GI carcinogenic effect. The 17 identified human epidemiological studies reported the ingestion of asbestos-contaminated water with concentrations from 1 to 71,350 million fibers per liter (MFL). A majority of the epidemiology studies reported statistically significant increases in multiple GI-specific cancers. However, these findings are confounded due to several critical study limitations including flawed study design, small sample size, selection bias, lack of individual exposure history, lack of adequate latency, and the inability to account for confounders including occupational history, diet, and smoking history. Based on our weight-of-evidence assessment, there is insufficient evidence of causality between the ingestion of asbestos and an increased incidence of GI cancers.

Risk of gastrointestinal cancers from inhalation and ingestion of asbestos

This paper summarizes the weight of epidemiological evidence to evaluate the hypothesis that asbestos exposure is causally associated with increased risk of gastrointestinal (GI) cancers as suggested by Selikoff in an early study of insulation workers. This review looks at populations that develop GI cancers, namely stomach, colorectal, colon and rectal. Guidelines for assessing causality are strength of association, biological gradient and consistency of the associations. Exposure–response (E–R) was evaluated using three methods to estimate exposure. Rate Ratios (RRs) for lung cancer and percent of mesothelioma are used as surrogate measures of asbestos exposure for all the cohorts of exposed workers. Quantitative or semi-quantitative estimates of cumulative exposure to asbestos were also used to assess E–R trends and were compared to E–R trends for lung cancer and mesothelioma in individual studies. Surrogate measures are important since there are few individual studies that have assessed E–R. None of the various methods to estimate asbestos exposure yielded consistent E–R trends and the strength of the associations were consistently weak or non-existent for the four types of GI cancers. The epidemiological evidence detracts from the hypothesis that occupational asbestos exposure increases the risk of stomach, colorectal, colon, and rectal cancer. Findings are briefly summarized below.

Malignant peritoneal mesothelioma in a 76-year-old woman with a history of asbestos fiber ingestion

We report on a woman with malignant mesothelioma of the peritoneum. This is the first report of a subject with this disease who revealed a history of asbestos ingestion by asbestos-contaminated food. She presented with episodes of sweating and fever, ascites, and weight loss. At laparotomy, small tumor deposits were noted on the peritoneum. The omental cake was removed, together with the uterus, ovaries, and tubes which were all macroscopically normal. The diagnosis was established by immunohistochemistry and electron microscopy. Postoperatively, her complaints of fever and sweating disappeared. She refused further chemotherapy. After questioning her for asbestos exposure, she told us that, years ago, she used to prepare vegetables for cooking in rain water collected from a roof made of asbestos.

Asbestos in water

Abstract Asbestos is not uncommon in water, usually originating from asbestos‐cement pipes or asbestos‐containing aquifers. Although asbestos concentrations are typically less than one million fibers per liter, concentrations have occasionally exceeded one billion fibers per liter. Some epi‐demiological and laboratory‐animal studies have revealed an association of asbestos ingestion with various types of cancer, while other studies have not. Ingested asbestos, usually short fibers, is capable of penetrating the intestinal wall and being eliminated in urine or accumulating in various tissues and organs. Elevated asbestos concentrations have recently been detected in colon cancers of asbestos workers. Drinking‐water systems should attempt to minimize asbestos concentrations by focusing on actual or potential sources of asbestos. Transmission electron microscopy is the analytical method of choice but revisions are needed in the U.S. method to accommodate recently promulgated drinking‐water standards. Laboratory studies have demonstrated deleterious effects of waterborne asbestos on individual aquatic organisms, but ecosystem‐wide effects are largely unknown.

Report on cancer risks associated with the ingestion of asbestos. DHHS Committee to Coordinate Environmental and Related Programs.

This report is an assessment of all available literature that pertains to the potential risk of cancer associated with ingestion of asbestos. It was compiled by a working group to assist policy makers in the Department of Health and Human Services determine if adequate information was available for a definitive risk assessment on this potential problem and evaluate if the weight of evidence was sufficient to prioritize this issue for new policy recommendations. The work group considered the basis for concern over this problem, the body of toxicology experiments, the individual epidemiologic studies which have attempted to investigate this issue, and the articles that discuss components of risk assessment pertaining to the ingestion of asbestos. In the report, the work group concluded: that no direct, definitive risk assessment can be conducted at this time; that further epidemiologic investigations will be very costly and only possess sufficient statistical power to detect relatively large excesses in cancers related to asbestos ingestion; and that probably the most pertinent toxicologic experiments relate to resolving the differences in how inhaled asbestos, which is eventually swallowed, is biologically processed by humans, compared to how ingested asbestos is processed. The work group believes that the cancer risk associated with asbestos ingestion should not be perceived as one of the most pressing potential public health hazards facing the nation. However, the work group does not believe that information was sufficient to assess the level of cancer risk associated with the ingestion and therefore, this potential hazard should not be discounted, and ingestion exposure to asbestos should be eliminated whenever possible.

Report on Cancer Risks Associated with the Ingestion of Asbestos

Cancer risks associated with ingestion of asbestos are discussed. Asbestos contamination of drinking water is considered. At least 66.5% of the United States water systems are capable of eroding asbestos cement pipes. The ability of water to leach asbestos from asbestos cement pipes can be modified by coatings applied to the inside pipe surface. Asbestos contamination in foods or pharmaceuticals is discussed. Asbestos fibers at concentrations of 1.1 to 172.7 million fibers per liter have been found in beverages. To date, studies supported by the Food and Drug Administration (FDA) have provided no evidence that ingesting asbestos results in an increased cancer risk. The FDA has determined that no prohibition on using asbestos filters in processing food, beverages, and non-parenteral drugs is needed. Toxicological studies on asbestos ingestion and carcinogenicity are reviewed. Epidemiological evaluations of the association between drinking-water supplies containing asbestos and cancer mortality are discussed. It is concluded that the available information is insufficient for assessing the risk of cancer associated with ingesting asbestos.

Report on cancer risks associated with the ingestion of asbestos. DHHS Committee to Coordinate Environmental and Related Programs

Report on cancer risks associated with the ingestion of asbestos. DHHS Committee to Coordinate Environmental and Related Programs

Particles and macrophages in murine Peyer's patches.

Mice were given 1% suspensions of 5 insoluble particles (chrysotile asbestos, quartz, carmine, carbon, and iron oxide) in drinking water for 3 months. The particles were subsequently sought in intestinal Peyer's patches by light microscopy. Carbon and iron oxide particles were visible in Peyer's patch macrophages, particularly in the subepithelial region, but the other particles could not be detected. The findings suggest that particle surface properties as well as particle size govern accumulation in Peyer's patches. The cytochemistry of subepithelial, mid-dome, tingible-body, and serosal macrophages of control mice indicated diversity of macrophages within the patch. Macrophages of asbestos-fed mice contained more lysosomes than macrophages of controls. Macrophage abundance in the dome apex was not significantly altered by asbestos ingestion. The other particles did not produce detectable alterations in macrophage morphology.

Asbestos in Drinking Water: A Canadian View

For several years now, public health professionals have been faced with evaluating the potential hazards associated with the ingestion of asbestos in food and drinking water. In Canada, this is a subject of particular concern, because of the widespread occurrence of chrysotile asbestos in drinking water supplies. The results of available Canadian monitoring and epidemiologic studies of asbestos in drinking water are reviewed and discussed in light of other published work. It is concluded that the risk to health associated with the ingestion of asbestos, at the levels found in municipal drinking water supplies, is so small that it cannot be detected by currently available epidemiologic techniques.

Asbestos in drinking water: a Canadian view.

For several years now, public health professionals have been faced with evaluating the potential hazards associated with the ingestion of asbestos in food and drinking water. In Canada, this is a subject of particular concern, because of the widespread occurrence of chrysotile asbestos in drinking water supplies. The results of available Canadian monitoring and epidemiologic studies of asbestos in drinking water are reviewed and discussed in light of other published work. It is concluded that the risk to health associated with the ingestion of asbestos, at the levels found in municipal drinking water supplies, is so small that it cannot be detected by currently available epidemiologic techniques.

Observations of cancer incidence surveillance in Duluth, Minnesota.

In 1973, amphibole asbestos fibers were discovered in the municipal water supply of Duluth, Minnesota. The entire city population of approximately 100,000 was exposed from the late 1950s through 1976 at levels of 1-65 million fibers per liter of water. Because of previous epidemiologic studies that linked mesothelioma, lung and gastrointestinal cancers to occupational exposure to asbestos, surveillance of cancer incidence in residents of Duluth was initiated to determine the health effect from ingestion of asbestos. The methodology of the Third National Cancer Survey (TNCS) and SEER Program was used. Duluth 1969-1971 rates were compared with TNCS rates for the cities of Minneapolis and St. Paul during 1969-1971; Duluth rates during 1974-1976 are compared with Duluth 1969-1971; Duluth rates during 1979-1980 are compared with Duluth 1969-1971 and with Iowa SEER; and a table of the occurrence of malignant mesothelioma is presented. Statistically significant excesses are observed in several primary sites in Duluth residents. However, lung cancer in Duluth females is the only primary site considered also of biological significance. The mesothelioma incidence rate is no more than expected. This paper also describes the problems of long-term surveillance of exposed populations considered at risk of environment cancer, the need for improved study methodologies and the use of federal records for follow up of exposed individuals.

Observations of Cancer Incidence Surveillance in Duluth, Minnesota

In 1973, amphibole asbestos fibers were discovered in the municipal water supply of Duluth, Minnesota. The entire city population of approximately 100,000 was exposed from the late 1950s through 1976 at levels of 1-65 million fibers per liter of water. Because of previous epidemiologic studies that linked mesothelioma, lung and gastrointestinal cancers to occupational exposure to asbestos, surveillance of cancer incidence in residents of Duluth was initiated to determine the health effect from ingestion of asbestos. The methodology of the Third National Cancer Survey (TNCS) and SEER Program was used. Duluth 1969-1971 rates were compared with TNCS rates for the cities of Minneapolis and St. Paul during 1969-1971; Duluth rates during 1974-1976 are compared with Duluth 1969-1971; Duluth rates during 1979-1980 are compared with Duluth 1969-1971 and with Iowa SEER; and a table of the occurrence of malignant mesothelioma is presented. Statistically significant excesses are observed in several primary sites in Duluth residents. However, lung cancer in Duluth females is the only primary site considered also of biological significance. The mesothelioma incidence rate is no more than expected. This paper also describes the problems of long-term surveillance of exposed populations considered at risk of environment cancer, the need for improved study methodologies and the use of federal records for follow up of exposed individuals.

Review of published studies on gut penetration by ingested asbestos fibers.

During the 1970s, potential health risks associated with exposure to asbestos in drinking water became a national concern. One of the key questions that arose from debate over whether ingestion of mineral fibers could result in increased gastrointestinal cancer risk was whether fibers can penetrate the gastrointestinal mucosa and thus have some chance of residing in tissue. It is likely that such movement of a large number of fibers is a necessary precursor for carcinogenesis following ingestion of asbestos. Studies of the potential for fiber accumulation in tissues and body fluids following introduction of asbestos to the alimentary canal have provided seemingly contradictory observations. This review, which places particular emphasis on the impact of experimental and analytical limitations on the evidential strengths of each study, indicates the likelihood that a very small fraction of ingested microscopic asbestos fibers penetrates the gastrointestinal mucosa. A reliable estimate of the magnitude of long-term fiber retention in tissues as a consequence of chronic human ingestion of asbestos cannot be made at this time.

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?

Although there have been a number of studies on the ingestion of asbestos, few studies exist on how the chrysotile asbestos itself is altered by the exposure to the acid stomach environment. This study has found that there are changes in the physical, chemical and surface properties of chrysotile asbestos as a result of exposure to water, strong acids, and simulated gastric juices. It was observed that the charge on the surface (the zeta 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 hydronium ion (H3O+), replaces the lost magnesium ion.

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?

Although there have been a number of studies on the ingestion of asbestos, few studies exist on how the chrysotile asbestos itself is altered by the exposure to the acid stomach environment. This study has found that there are changes in the physical, chemical and surface properties of chrysotile asbestos as a result of exposure to water, strong acids, and simulated gastric juices. It was observed that the charge on the surface (the zeta 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 hydronium ion (H3O+), replaces the lost magnesium ion.

Transmigration of ingested asbestos.

There has been speculation that the ingestion of asbestos in food and drinking water may play some role in the etiology of cancer of the gastrointestinal (GI) tract. An important question in the evaluation of the possible human cancer risk associated with asbestos ingestion is whether fibers can penetrate into and through the GI tract in sufficient numbers to cause adverse systemic or local effects. Factors that complicate interpretation of the available data on the transmigration of ingested asbestos are discussed, and the preliminary results of our ongoing investigation of the penetration of amosite fibers into the normal and abnormal intestinal mucosa of the Wistar rat are reported.

Relative source contributions of diet and air to ingested asbestos exposure.

Reliable assessments of the relative contributions of diet (food, beverages, and orally administered drugs) and air (inhaled fibers) to total ingested asbestos exposure are not feasible due to the paucity of quantitative data on the subject. Instead, scenarios for both modes of exposure were developed from the limited information available to give crude estimates of ingestion of asbestos from these routes. They suggest that such sources are potentially significant relative to the contribution of asbestos exposure derived from drinking water. Research recommendations are discussed.

Relative Source Contributions of Diet and Air to Ingested Asbestos Exposure

Reliable assessments of the relative contributions of diet (food, beverages, and orally administered drugs) and air (inhaled fibers) to total ingested asbestos exposure are not feasible due to the paucity of quantitative data on the subject. Instead, scenarios for both modes of exposure were developed from the limited information available to give crude estimates of ingestion of asbestos from these routes. They suggest that such sources are potentially significant relative to the contribution of asbestos exposure derived from drinking water. Research recommendations are discussed.

Commentary: Asbestos Penetration of the Gastrointestinal Tract

My comments are restricted to studies involving gastrointestinal exposure of humans and animals to asbestos via the diet or intubation. There have been three studies designed to determine whether human ingestion of asbestos in drinking water could result in the detection of asbestos in urine or postmortem tissues (1-3). One study concluded that ingested asbestos could not be found in human urine (1). However, other studies found evidence that ingested asbestos could penetrate the GI tract, migrate, and be recovered in urine and tissues (2,3). These two positive human studies were uncontrolled to the extent that inhaled asbestos may have contributed to the positive findings. Hence, we look to controlled animal studies for confirmation of the human findings, especially with regard to dose. There have been at least 12 animal studies involving rats and baboons (4-15). Five rat studies (4-8) and two baboon studies (8-10) presented evidence of asbestos penetration of the GI tract and/or migration to various tissues. Three rat studies (11-13) and two baboon studies (14, 15) found little or no evidence of penetration and migration. The positive animal findings (4-10) are not completely convincing for various reasons: (a) the number of fibers observed on a grid opening basis was quite small (8, 10); (b) the qualitative presentation of data prevented numerical comparisons of test and control fiber count data (4,6); (c) too few control data were obtained (7); and (d) fiber count data were reported in terms of fibers per milligram or milliliter (5). Unless fiber count data are given in terms of fibers per grid opening, it is not possible to know whether the authors' conclusions are based on the observation of one or hun-

An investigation of the penetration of ingested asbestos into the normal and abnormal intestinal mucosa of the rat

To characterize the tissue response associated with the presence of asbestos fibres in the gastro-intestinal wall, duodenal tissues of Wistar rats were examined by light microscopy following injection of a suspension containing amosite fibres into the wall of the duodenum. Intestinal tissues were also examined by light microscopy following oral administration of amosite for 5 days to healthy animals and for up to 7 days to animals with induced gastro-intestinal ulcers. Injection of amosite into the wall of the gastro-intestinal tract resulted in granulomatous lesions characterized by large numbers of macrophages containing crystals with the polarizing characteristics of amosite fibres. Examination by polarizing light microscopy following ingestion of asbestos revealed no such lesions or other histopathological abnormalities in the gut wall of the healthy animals and no intracellular fibres were observed in the animals with ulcers. Light microscopy, therefore, yielded no pathological evidence of widespread transmigration of asbestos from the gastro-intestinal tract of rats, even under conditions of mucosal loss. Further studies involving analysis by electron microscopy are under way.