Nevada desert dust with heavy metals suppresses IgM antibody production

Abstract

Systemic health effects from exposure to a complex natural dust containing heavy metals from the Nellis Dunes Recreation Area (NDRA) near Las Vegas, NV, were evaluated. Several toxicological parameters were examined following lung exposure to emissive dust from three geologic sediment types heavily used for recreational off-road activities: yellow sand very rich in arsenic (termed CBN 5); a shallow cover of loose dune sand overlying a gravelly subsoil bordering dune fields (termed CBN 6); and brown claystone and siltstone (termed CBN 7). Adult female B6C3F1 mice were exposed by oropharyngeal administration to these three types of geogenic dusts at 0.01-100 mg of dust/kg of body weight, once per week for four weeks. The median grain sizes were 4.6, 3.1, and 4.4 μm, for CBN 5, 6, and 7, respectively. Each type of dust contained quantifiable amounts of aluminum, vanadium, chromium, manganese, iron, cobalt, copper, zinc, arsenic, strontium, cesium, lead, uranium, and others. Descriptive markers of immunotoxicity, neurotoxicity, hematology, and clinical chemistry parameters were assessed. Notable among all three CBN units was a systemic, dose-responsive decrease in antigen-specific IgM antibody responses. Geogenic dust from CBN 5 produced more than a 70% suppression in IgM responses, establishing a lowest adverse effect level (LOAEL) of 0.01 mg/kg. A suppression in IgM responses and a corresponding increase in serum creatinine determined a LOAEL of 0.01 mg/kg for CBN 6. The LOAEL for CBN 7 was 0.1 mg/kg and also was identified from suppression in IgM responses. These results are of concern given the frequent off-road vehicle traffic and high visitor rates at the NDRA, estimated at 300,000 each year.

Keywords: Geogenic dust; Heavy metals; Immunotoxicity; Neurotoxicity; Particulate matter.

Graphical abstract

Fig. 1

Toxicology sample collection arrangement.

Fig. 2

Liver somatic index (liver weight corrected by body weight) of adult female B6C3F1 mice following oropharyngeal aspiration exposure to dust samples from NDRA CBN 5 or CBN 6. Data are presented as mean ± standard deviation. Sample size for each group was 5–6 animals. The (*) indicates a response statistically different from the 0 mg/kg group (p < 0.05) for that CBN unit.

Fig. 3

Sheep red blood cell-specific-IgM antibody production in adult female B6C3F1 mice following oropharyngeal aspiration exposure to dust samples from NDRA CBN 5 (A), 6 (B), and 7 (B). Data are presented as mean ± standard error of the mean. Sample size for each group was 4–6 animals. Data presented are representative of three trial days. The (*) indicates a response statistically different from the 0 mg/kg group (p < 0.05) for that CBN unit and was determined from log transformed data.

Fig. 4

Splenic natural killer cell activity in adult female B6C3F1 mice following oropharyngeal aspiration exposure to exposure to dust samples from NDRA CBN 5 or 6. Data are presented as mean lytic unit ± standard error of the mean. Sample size for each group was 5–6 animals. Data presented are representative of three trial days. The (*) indicates data significantly different from the 0 mg/kg group (p < 0.05) for that CBN unit.

Fig. 5

Autoantibody production against (A) myelin basic protein (IgM and IgG) or (B) glial fibrillary acidic protein (IgM and IgG) in adult female B6C3F1 mice following oropharyngeal aspiration exposure to dust samples from NDRA CBN 6. Data are presented as mean ± standard deviation. Sample size for each group was 5–6 animals. The (*) indicates a response statistically different from the 0 mg/kg group (p < 0.05).

Fig. 6

Average number of CD3+ T cells observed in brains of adult female B6C3F1 mice following oropharyngeal aspiration exposure to dust samples from NDRA CBN 7. Data are presented as mean ± standard deviation. Sample size for each group was 5–6 animals. The (*) indicates a response statistically different from the 0 mg/kg group (p < 0.05).