Investigating palygorskite's role in the development of mesothelioma in southern Nevada: Insights into fiber-induced carcinogenicity.

Similar to asbestos fibers, nonregulated mineral fibers can cause malignant mesothelioma (MM). Recently, increased proportions of women and young individuals with MM were identified in southern Nevada, suggesting that environmental exposure to carcinogenic fibers was causing the development of MM. Palygorskite, a fibrous silicate mineral with a history of possible carcinogenicity, is abundant in southern Nevada. In this study, our aim was to determine whether palygorskite was contributing to the development of MM in southern Nevada. While palygorskite, in vitro, displayed some cytotoxicity toward primary human mesothelial (HM) cells and reduced their viability, the effects were roughly half of those observed when using similar amounts of crocidolite asbestos. No Balb/c (0/19) or MexTAg (0/18) mice injected with palygorskite developed MM, while 3/16 Balb/c and 13/14 MexTAg mice injected with crocidolite did. Lack of MM development was associated with a decreased acute inflammatory response, as injection of palygorskite resulted in lower percentages of macrophages (p = .006) and neutrophils (p = .02) in the peritoneal cavity 3 d after exposure compared to injection of crocidolite. Additionally, compared to mice injected with crocidolite, palygorskite-injected mice had lower percentages of M2 (tumor-promoting) macrophages (p = .008) in their peritoneal cavities when exposed to fiber for several weeks. Our study indicates that palygorskite found in the environment in southern Nevada does not cause MM in mice, seemingly because palygorskite, in vivo, fails to elicit inflammation that is associated with MM development. Therefore, palygorskite is not a likely contributor to the MM cases observed in southern Nevada.

Health effects following subacute exposure to geogenic dust collected from active drainage surfaces (Nellis Dunes Recreation Area, Las Vegas, NV).

The specific health effects of direct inhalation of fine minerogenic dusts generated by natural soil surfaces remain poorly known and relatively little researched. To learn more about this exposure and its contribution to human health effects, we surveyed surface sediment and characterized dust from the Nellis Dunes Recreation Area (NDRA) in Clark County, Nevada, a popular off-road vehicle (ORV) recreational site. Dry drainage systems at NDRA are commonly used as natural trail systems for ORV recreation; these surfaces also are characterized by high concentrations of heavy metals. Geogenic dust with a median diameter of 4.05 µm, collected from drainage surfaces at NDRA contained a total elemental concentration of aluminum (79,651 µg/g), vanadium (100 µg/g), chromium (54 µg/g), manganese (753 µg/g), iron (33,266 µg/g), cobalt (14 µg/g), copper (37 µg/g) zinc (135 µg/g), arsenic (71 µg/g), strontium (666 µg/g), cesium (15 µg/g), lead (34 µg/g), and uranium (54.9 µg/g). Adult female B6C3F1 mice exposed via oropharyngeal aspiration to 0.01-100 mg dust/kg body weight, four times, a week apart, for 28-days, were evaluated for immuno- and neurotoxicological outcomes 24 h after the last exposure. Antigen-specific IgM responses were dose-responsively suppressed at 0.1, 1.0, 10 and 100 mg/kg. Splenic lymphocytic subpopulations, hematological and clinical chemistry parameters were affected. In brain tissue, antibodies against NF-68, and GFAP were not affected, whereas IgM antibodies against MBP were reduced by 26.6% only in the highest dose group. A lowest observed adverse effect level (LOAEL) of 0.1 mg/kg/day and a no observed adverse effect level (NOAEL) of 0.01 mg/kg/day were derived based on the antigen primary IgM responses after subacute exposure to this geogenic dust.

Surface and Airborne Arsenic Concentrations in a Recreational Site near Las Vegas, Nevada, USA.

Elevated concentrations of arsenic, up to 7058 µg g(-1) in topsoil and bedrock, and more than 0.03 µg m(-3) in air on a 2-week basis, were measured in the Nellis Dunes Recreation Area (NDRA), a very popular off-road area near Las Vegas, Nevada, USA. The elevated arsenic concentrations in the topsoil and bedrock are correlated to outcrops of yellow sandstone belonging to the Muddy Creek Formation (≈ 10 to 4 Ma) and to faults crossing the area. Mineralized fluids moved to the surface through the faults and deposited the arsenic. A technique was developed to calculate airborne arsenic concentrations from the arsenic content in the topsoil. The technique was tested by comparing calculated with measured concentrations at 34 locations in the NDRA, for 3 periods of 2 weeks each. We then applied it to calculate airborne arsenic concentrations for more than 500 locations all over the NDRA. The highest airborne arsenic concentrations occur over sand dunes and other zones with a surficial layer of aeolian sand. Ironically these areas show the lowest levels of arsenic in the topsoil. However, they are highly susceptible to wind erosion and emit very large amounts of sand and dust during episodes of strong winds, thereby also emitting much arsenic. Elsewhere in the NDRA, in areas not or only very slightly affected by wind erosion, airborne arsenic levels equal the background level for airborne arsenic in the USA, approximately 0.0004 µg m(-3). The results of this study are important because the NDRA is visited by more than 300,000 people annually.

The Presence of Asbestos in the Natural Environment is Likely Related to Mesothelioma in Young Individuals and Women from Southern Nevada.

BACKGROUND: Inhalation of asbestos and other mineral fibers is known causes of malignant mesothelioma (MM) and lung cancers. In a setting of occupational exposure to asbestos, MM occurs four to eight times more frequently in men than in women, at the median age of 74 years, whereas an environmental exposure to asbestos causes the same number of MMs in men and women, at younger ages. METHODS: We studied the geology of Nevada to identify mineral fibers in the environment. We compared MM mortality in different Nevada counties, per sex and age group, for the 1999 to 2010 period. RESULTS: We identified the presence of carcinogenic minerals in Nevada, including actinolite asbestos, erionite, winchite, magnesioriebeckite, and richterite. We discovered that, compared with the United States and other Nevada counties, Clark and Nye counties, in southern Nevada, had a significantly higher proportion of MM that occurred in young individuals (<55 years) and in women. CONCLUSIONS: The elevated percentage of women and individuals younger than 55 years old, combined with a sex ratio of 1:1 in this age group and the presence of naturally occurring asbestos, suggests that environmental exposure to mineral fibers in southern Nevada may be contributing to some of these mesotheliomas. Further research to assess environmental exposures should allow the development of strategies to minimize exposure, as the development of rural areas continues in Nevada, and to prevent MM and other asbestos-related diseases.