Historical ambient airborne asbestos concentrations in the United States – an analysis of published and unpublished literature (1960s–2000s)

Abstract

Outdoor concentrations of airborne asbestos have been measured throughout the US over time. However, a thorough review and analysis of these data has not been conducted. The purpose of this study is to characterize asbestos concentrations in ambient air by environment type (urban, rural) and by decade, using measurements collected in the absence of known asbestos emission sources. A total of 17 published and unpublished studies and datasets were identified that reported the results of 2058 samples collected from the 1960s through the 2000s across the US. Most studies did not report asbestos fiber type, and data based on different analytical methods (e.g. Phase Contrast Microscopy, Transmission Electron Microscopy, etc.) were combined in the dataset; however, only fibers ≥5 μm in length were considered. For a small subset of the measurements (n = 186, 9.0%), a conversion factor was used to convert mass-based data (e.g. ng/m³) to count-based values (i.e. f/cc ≥5 μm). The estimated overall mean and median ambient asbestos concentrations for the 1960s through 2000s were 0.00093 f/cc and 0.00022 f/cc, respectively. Concentrations generally increased from the 1960s through the early 1980s, after which they declined considerably. While asbestos use decreased throughout the 1970s, these results indicate that ambient concentrations peaked during the early 1980s, which suggests the possible contribution of abatement or demolition activities. Lastly, ambient asbestos concentrations were higher in urban than rural settings, which is consistent with the greater use of asbestos-containing materials in more densely populated areas.

• Ambient levels
• asbestos
• fibers
• outdoor concentrations

Acknowledgements

The authors would like to thank Dr Peter Ruestow of Cardno ChemRisk and Dr Brent D. Kerger of Exponent for providing valuable technical feedback. In addition, we thank Dr Richard J. Lee and Drew Van Orden of the RJ Lee Group for giving us permission to use their data in this analysis.

Declaration of interest

Cardno ChemRisk is a consulting firm which has been engaged by companies that have been, and are, involved in asbestos-related litigation, to provide general consulting and expert advice on scientific matters, as well as litigation support. This work was funded in its entirety by Cardno ChemRisk, and the preparation of the paper is the exclusive professional work of the authors. Drs Pierce and Paustenbach have served as experts in asbestos-related litigation, and they, along with others, may be called upon in the future to serve as expert witnesses in related litigation.

Supplementary material available online

Supplementary Appendices A and B