Asbestos and embryonic development

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.

Nonpulmonary outcomes of asbestos exposure

The adverse pulmonary effects of asbestos are well accepted in scientific circles. However, the extrapulmonary consequences of asbestos exposure are not as clearly defined. In this review the potential for asbestos to produce diseases of the peritoneum, immune, gastrointestinal (GIT), and reproductive systems are explored as evidenced in published, peer-reviewed literature. Several hundred epidemiological, in vivo, and in vitro publications analyzing the extrapulmonary effects of asbestos were used as sources to arrive at the conclusions and to establish areas needing further study. In order to be considered, each study had to monitor extrapulmonary outcomes following exposure to asbestos. The literature supports a strong association between asbestos exposure and peritoneal neoplasms. Correlations between asbestos exposure and immune-related disease are less conclusive; nevertheless, it was concluded from the combined autoimmune studies that there is a possibility for a higher-than-expected risk of systemic autoimmune disease among asbestos-exposed populations. In general, the GIT effects of asbestos exposure appear to be minimal, with the most likely outcome being development of stomach cancer. However, IARC recently concluded the evidence to support asbestos-induced stomach cancer to be "limited." The strongest evidence for reproductive disease due to asbestos is in regard to ovarian cancer. Unfortunately, effects on fertility and the developing fetus are under-studied. The possibility of other asbestos-induced health effects does exist. These include brain-related tumors, blood disorders due to the mutagenic and hemolytic properties of asbestos, and peritoneal fibrosis. It is clear from the literature that the adverse properties of asbestos are not confined to the pulmonary system.

Asbestos: toxicology and risk assessment for the general population in The Netherlands

Within the scope of the preparation of Integrated Criteria Documents for priority compounds in The Netherlands, the possible health effects of oral and inhalatory exposure to asbestos for the general population were evaluated. It was concluded from the results of experiments in animals that exposure to asbestos by the oral route is not carcinogenic and is not expected to present a health risk to the general population. Inhaled asbestos, however, is distinctly carcinogenic to man, giving rise to lung tumours, and mesotheliomas of the pleura and peritoneum. Chrysotile asbestos appears to be less potent in inducing mesotheliomas than the amphiboles, but all types of asbestos appear to have a similar potency for inducing lung cancer. The risk of mesothelioma is not expected to be influenced by smoking, whereas the risk of lung cancer is expected to be ten times higher in smokers than in non-smokers exposed to the same asbestos concentrations. Risk-assessment models for the inhalatory route, for the general population, are based on linear non-threshold extrapolation of occupational exposure to much lower environmental concentrations. These models give only a rough approximation of the risk of environmental exposure to asbestos. In accordance with the Air Quality Guidelines of the World Health Organization (World Health Organization, 1987), it was estimated that an extra risk of lung cancer of one in 10(6) (in the general population, with 30% smokers) may be presented by lifetime exposure to asbestos fibres longer than 5 microns, measured by electron microscopy, at concentrations of 100-1000/m3. It was further estimated that an extra risk of mesothelioma of one in 10(6) may be presented by lifetime exposure to 10-100 amphibole fibres/m3 or to a range of 100-10000 chrysotile fibres/m3 (fibres longer than 5 microns). From the current asbestos concentrations, the risk of mesothelioma for the general population in The Netherlands appears to be negligible; the extra risk of lung cancer is expected to be higher than 1 in 10(6) near asbestos sources, whereas it appears to be negligible in background areas and in most large cities and industrial areas. However, it must be borne in mind that the validity of the risk figures given is difficult to judge.

Factors affecting survival of deep frozen bovine embryos in vitro: The effect of freezing container and method of removing cryoprotectant

The effect of freezing container and method of glycerol removal on in vitro survival of frozen-thawed Day 7 bovine embryos was investigated. Two hundred and fifteen embryos were frozen in ampules or straws, in either vertical or horizontal position and at a cooling rate of 0.3 degrees C/minute from -7 degrees C to -35 degrees C, before being plunged into liquid nitrogen. Samples were thawed in a water bath at +35 degrees C and glycerol was removed by either step-wise dilution (increments 0.25 M) or by exposure to 1.0 M sucrose for 10 minutes. A total of 197 embryos was recovered post-thaw (91%) with an overall survival after 1, 3, 6 and 24 hours in culture of 87, 81, 71, and 23%, respectively. Embryonic quality and percent survival, as assessed morphologically, did not change significantly between 1 and 3 hours but decreased significantly between 6 and 24 hours in culture (p < 0.05). Survival at 24 hours was significantly higher after removal of the cryoprotectant with sucrose when compared to the step-wise glycerol dilution (p < 0.05). Overall, embryonic survival in straws equaled that in ampules; freezing orientation of straws did not affect results. Further, glycerol removal with sucrose tended to yield survival superior to that provided by a step-wise dilution technique.