Using lichen chemistry to assess airborne tungsten and cobalt in Fallon, Nevada

Adsorption, Desorption and Bioavailability of Tungstate in Mediterranean Soils

The adsorption and desorption process of the tungstate ion was studied in three soils characteristic of the Mediterranean area, with particularly reference to bioavailability pathways. In the three soils examined, the tungstate adsorption was described by a Langmuir-type equation, while the desorption process showed that not all the adsorbed tungstate was released, probably due to the formation of different bonds with the adsorbing soil surfaces. The pH was found to be the main soil property that regulates the adsorption/desorption: The maximum adsorption occurred in the soil with the acidic pH, and the maximum desorption in the most basic soil. In addition, the organic matter content played a fundamental role in the adsorption of tungstate by soils, being positively correlated with the maximum of adsorption. These results indicate that the lowest bioavailability should be expected in the acidic soil characterized by the highest adsorption capacity. This is confirmed by the trend of the maximum buffer capacity (MBC) of soils which is inversely related to bioavailability, and was the highest in the acidic soil and the lowest in the most basic soil. Our data could contribute in drafting environmental regulations for tungsten that are currently lacking for Mediterranean soils.

Influence of Increasing Tungsten Concentrations and Soil Characteristics on Plant Uptake: Greenhouse Experiments with Zea mays

Tungsten is largely used in high-tech and military industries. Soils are increasingly enriched in this element, and its transfer in the food chain is an issue of great interest. This study evaluated the influence of soil characteristics on tungsten uptake by Zea mays grown on three soils, spiked with increasing tungsten concentrations. The soils, classified as Histosol, Vertisol, and Fluvisol, are characteristic of the Mediterranean area. The uptake of the element by Zea mays was strictly dependent on the soil characteristics. As the pH of soils increases, tungsten concentrations in the roots and shoots of the plants increased. Also, humic substances showed a great influence on tungsten uptake, which decreased with increasing organic matter of soils. Tungsten uptake by Zea mays can be described by a Freundlich-like equation. This soil-to-plant transfer model may be useful in promoting environmental regulations on the hazards of this element in the environment.

Tungstate adsorption onto Italian soils with different characteristics

The study of tungsten in the environment is currently of considerable interest because of the growing concerns resulting from its possible toxicity and carcinogenicity. Adsorption reactions are some of the fundamental processes governing the fate and transport of tungsten compounds in soil. This paper reports data on the adsorption of tungstate ions in three different Italian soils, which are characteristic of the Mediterranean region. The results show that pH is the most important factor governing the adsorption of tungstate in these soils. The data interpreted according to the Langmuir equation show that the maximum value of adsorption is approximately 30 mmol kg^-1 for the most acidic soil (pH = 4.50) and approximately 9 mmol kg^-1 for the most basic soil (pH = 7.40). In addition, soil organic matter is shown to play a fundamental role in adsorption processes, which are favored in soils with a higher organic matter content. The data could contribute to a better understanding of the behavior of tungsten compounds in Italian soils for which current knowledge is very scarce, also in view of environmental regulations, which are currently lacking.

Comparison of size and geography of airborne tungsten particles in Fallon, Nevada, and Sweet Home, Oregon, with implications for public health

To improve understanding of possible connections between airborne tungsten and public health, size and geography of airborne tungsten particles collected in Fallon, Nevada, and Sweet Home, Oregon, were compared. Both towns have industrial tungsten facilities, but only Fallon has experienced a cluster of childhood leukemia. Fallon and Sweet Home are similar to one another by their particles of airborne tungsten being generally small in size. Meteorologically, much, if not most, of residential Fallon is downwind of its hard metal facility for at least some fraction of time at the annual scale, whereas little of residential Sweet Home is downwind of its tungsten facility. Geographically, most Fallon residents potentially spend time daily within an environment containing elevated levels of airborne tungsten. In contrast, few Sweet Home residents potentially spend time daily within an airborne environment with elevated levels of airborne tungsten. Although it cannot be concluded from environmental data alone that elevated airborne tungsten causes childhood leukemia, the lack of excessive cancer in Sweet Home cannot logically be used to dismiss the possibility of airborne tungsten as a factor in the cluster of childhood leukemia in Fallon. Detailed modeling of all variables affecting airborne loadings of heavy metals would be needed to legitimately compare human exposures to airborne tungsten in Fallon and Sweet Home.

Tungsten toxicity

There is emerging evidence that tungsten has toxic health effects. We summarize the recent tungsten toxicity research in this short review. Tungsten is widely used in many commercial and military applications because it has the second highest melting temperature of any element. Consequently, it is important to elucidate the potential health effects of tungsten.

Exposure to sodium tungstate and Respiratory Syncytial Virus results in hematological/immunological disease in C57BL/6J mice

The etiology of childhood leukemia is not known. Strong evidence indicates that precursor B-cell Acute Lymphoblastic Leukemia (Pre-B ALL) is a genetic disease originating in utero. Environmental exposures in two concurrent, childhood leukemia clusters have been profiled and compared with geographically similar control communities. The unique exposures, shared in common by the leukemia clusters, have been modeled in C57BL/6 mice utilizing prenatal exposures. This previous investigation has suggested in utero exposure to sodium tungstate (Na2WO4) may result in hematological/immunological disease through genes associated with viral defense. The working hypothesis is (1) in addition to spontaneously and/or chemically generated genetic lesions forming pre-leukemic clones, in utero exposure to Na2WO4 increases genetic susceptibility to viral influence(s); (2) postnatal exposure to a virus possessing the 1FXXKXFXXA/V9 peptide motif will cause an unnatural immune response encouraging proliferation in the B-cell precursor compartment. This study reports the results of exposing C57BL/6J mice to Na2WO4 in utero via water (15 ppm, ad libetum) and inhalation (mean concentration PM5 3.33 mg/m3) and to Respiratory Syncytial Virus (RSV) within 2 weeks of weaning. Inoculation of C57BL/6J mice with RSV was associated with a neutrophil shift in 56% of 5-month old mice. When the RSV inoculation was combined with Na2WO4-exposure, significant splenomegaly resulted (p=0.0406, 0.0184, 0.0108 for control, Na2WO4-only and RSV-only, respectively) in addition to other hematological pathologies which were not significant. Exposure to Na2WO4 and RSV resulted in hematological/immunological disease, the nature of which is currently inconclusive. Further research is needed to characterize this potential leukemia mouse model.

Spatial patterns of tungsten and cobalt in surface dust of Fallon, Nevada

Spatial patterns of tungsten and cobalt are described for surface dust of Fallon, Nevada, where a cluster of childhood leukemia has been ongoing since 1997. In earlier research, airborne tungsten and cobalt was shown to be elevated in total suspended particulates in Fallon. To fine-tune the spatial patterns of tungsten and cobalt deposition in Fallon, surface dust was collected in a grid pattern within as well as outside of Fallon to establish background concentrations of metals. In surface dust, tungsten and cobalt show sharp peaks (934 ppm and 98 ppm, respectively) within Fallon just north of highway 50 and west of highway 95. These two peaks overlap spatially, and given the grid pattern used for collecting surface dust, the source area of these two airborne metals can be pinpointed to the vicinity of hard-metal industry located north of highway 50 and west of highway 95. Fallon is distinctive in west central Nevada because of high airborne tungsten and cobalt particulates, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne tungsten and cobalt particulates.

Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada

Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of < or = 1 microm and 5.9 microm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten.

Temporal variability of tungsten and cobalt in Fallon, Nevada

BACKGROUND

Since 1997, Fallon, Nevada, has experienced a cluster of childhood leukemia that has been declared "one of the most unique clusters of childhood cancer ever reported." Multiple environmental studies have shown airborne tungsten and cobalt to be elevated within Fallon, but the question remains: Have these metals changed through time in correspondence with the onset of the leukemia cluster?

METHODS

We used dendrochemistry, the study of element concentrations through time in tree rings, in Fallon to assess temporal variability of airborne tungsten and cobalt since the late 1980s. The techniques used in Fallon were also tested in a different town (Sweet Home, OR) that has airborne tungsten from a known source.

RESULTS

The Sweet Home test case confirms the accuracy of dendrochemistry for showing temporal variability of environmental tungsten. Given that dendrochemistry works for tungsten, tree-ring chemistry shows that tungsten increased in Fallon relative to nearby comparison towns beginning by the mid-1990s, slightly before the onset of the cluster, and cobalt has been high throughout the last approximately 15 years. Other metals do not show trends through time in Fallon.

DISCUSSION

Results in Fallon suggest a temporal correspondence between the onset of excessive childhood leukemia and elevated levels of tungsten and cobalt. Although environmental data alone cannot directly link childhood leukemia with exposure to metals, research by others has shown that combined exposure to tungsten and cobalt can be carcinogenic to humans.

CONCLUSION

Continued biomedical research is warranted to directly test for linkage between childhood leukemia and tungsten and cobalt.