Atmospheric measurements of semivolatile organic compounds (SOCs) were made at Mt. Bachelor Observatory (MBO), located in Oregon’s Cascade Range, to understand the trans-Pacific and regional transport of SOCs from urban areas. High volume air sampling (~644 m3 for 24 hour periods) of both the gas and particulate phases was conducted from the 19th of April 2004 to the 13th of May 2006 (n=69); including NASA’s INTEX-B campaign in spring 2006 (n= 34 of 69). Air mass back trajectories were calculated and used to calculate source region impact factors (SRIFs), the percentage of time the sampled air mass resided in a given source region. Particulate-phase polycyclic aromatic hydrocarbon (PAH) concentrations at MBO increased with the percentage of air mass time in Asia and, in conjunction with other data, provided strong evidence that particulate-phase PAHs are emitted from Asia and undergo trans-Pacific atmospheric transport to North America. Gas-phase PAH and fluorotelomer alcohol (FTOH) concentrations significantly increased with the percentage of air mass time in California’s urban areas, while retene and polychlorinated biphenyl (PCB) concentrations increased with the percentage of air mass time in Oregon and during regional fire events. In addition, Σgas-phase PAH, retene, and levoglucosan concentrations were significantly correlated (p-value < 0.001) with ΣPCB concentrations, suggesting increased atmospheric PCB concentrations were associated with fires due to the volatilization of stored PCBs from soil and vegetation.

Synopsis Driven by major scientific advances in analytical methods, biomonitoring, computational tools, and a newly articulated vision for a greater impact in public health, the field of exposure science is undergoing a rapid transition from a field of observation to a field of prediction. Deployment of an organizational and predictive framework for exposure science analogous to the “systems approaches” used in the biological sciences is a necessary step in this evolution. Here we propose the Aggregate Exposure Pathway (AEP) concept as the natural and complementary companion in the exposure sciences to the Adverse Outcome Pathway (AOP) concept in the toxicological sciences. Aggregate exposure pathways offer an intuitive framework to organize exposure data within individual units of prediction common to the field, setting the stage for exposure forecasting. Looking farther ahead, we envision direct linkages between aggregate exposure pathways and adverse outcome pathways, completing the source to outcome continuum for more efficient integration of exposure assessment and hazard identification. Together, the two pathways form and inform a decision-making framework with the flexibility for risk-based, hazard-based, or exposure-based decision making.

For the identification and assessment of persistent, bioaccumulative, and toxic (PBT) chemicals and persistent organic pollutants (POPs), overall persistence (P(ov)) and long-range transport potential (LRTP) are important indicators. In this article, we first give an overview of methods to determine P(ov) and LRTP and discuss the influence of multimedia partitioning of semivolatile organic chemicals (SOCs) on P(ov) and LRTP. Next, we summarize the most important features of various multimedia fate and transport models that can be used to calculate P(ov) and LRTP. Complementary to environmental fate models, field data provide important empirical information about the spatial distribution and time trends of SOC concentrations in the environment. We discuss the role of field data in the estimation of P(ov) and LRTP and give an overview of important field studies showing the levels and trends of various groups of chemicals in different parts of the world. Then, we address key topics in the field of PBT and POP assessment that require further research, such as the formation of transformation products, the influence of atmospheric aerosols on the degradation and transport of SOCs, and the effect of long-range transport by ocean currents. In addition, we describe the most important types of uncertainty associated with estimates of P(ov) and LRTP, which are mainly uncertainty of chemical property data and uncertainty of the design of environmental fate models. Finally, we illustrate the characterization of SOCs in terms of P(ov) and LRTP with the example of the consensus model for P(ov) and LRTP Tool that is provided by the Organization for Economic Cooperation and Development.

Historic and current use pesticides (HUPs and CUPs), with respect to use in the United States and Canada, were identified in trans-Pacific and regional air masses at Mt. Bachelor Observatory (MBO), a remote high elevation mountain in Oregon’s Cascade Range located in the United States, during the sampling period of April 2004 to May 2006 (n=69), including NASA’s INTEX-B campaign (spring 2006). Elevated hexachlorobenzene (HCB) and α-hexachlorocyclohexane (α-HCH) concentrations were measured during trans-Pacific atmospheric transport events at MBO, suggesting that Asia is an important source region for these HUPs. Regional atmospheric transport events at MBO resulted in elevated dacthal, endosulfan, metribuzin, triallate, trifluralin, and chlorpyrifos concentrations, with episodic increases in concentration during some spring application periods, suggesting that the Western U.S. is a significant source region for these CUPs. Endosulfan I, γ-HCH, and dacthal concentrations were significantly positively correlated (p-value < 0.05) with increased air mass time in Western U.S. agricultural areas. Elevated γ-HCH concentrations were measured at MBO during both trans-Pacific and regional atmospheric transport events, including regional fire events. In addition to γ-HCH, elevated Σchlordane, α-HCH, HCB, and trifluralin concentrations were associated with fires in Western North America due to revolatilization of these pesticides from soils and vegetation. Trans-chlordane/cis-chlordane and α-HCH/γ-HCH ratios were calculated and may be used to distinguish between free tropospheric and regional and/or Asian air masses.