PAH and OPAH Flux during the Deepwater Horizon Incident

Abstract

Passive sampling devices were used to measure air vapor and water dissolved phase concentrations of 33 polycyclic aromatic hydrocarbons (PAHs) and 22 oxygenated PAHs (OPAHs) at four Gulf of Mexico coastal sites prior to, during and after shoreline oiling from the Deepwater Horizon oil spill (DWH). Measurements were taken at each site over a 13 month period, and flux across the water-air boundary was determined. This is the first report of vapor phase and diffusive flux of both PAHs and OPAHs during the DWH. Vapor phase sum PAH and OPAH concentrations ranged between 6.6 and 210 ng/m3 and 0.02 and 34 ng/m3 respectively. PAH and OPAH concentrations in air exhibited different spatial and temporal trends than in water, and air-water flux of 13 individual PAHs was shown to be at least partially influenced by the DWH incident. The largest PAH volatilizations occurred at the sites in Alabama and Mississippi at nominal rates of 56,000 and 42,000 ng/m2/day in the summer. Naphthalene was the PAH with the highest observed volatilization rate of 52,000 ng/m2/day in June 2010. This work represents additional evidence of the DWH incident contributing to air contamination, and provides one of the first quantitative air-water chemical flux determinations with passive sampling technology.

Air-water exchange of PAHs and OPAHs at a superfund mega-site

“…Water concentration calculations were described in detail in Allan et al, 2012 (Allan et al, 2012). Air concentrations are further described in Tidwell et al, 2016 (Tidwell et al, 2016). Air and water concentration equations can be found in supplementary information equations S1-S10.…”

“…Highly contaminated waters may also be sources of contaminants to air (Tidwell et al, 2016). Aquatic Superfund sites, such as the Portland Harbor Superfund Mega-site (PHSM), have long been suspected sources of air pollution (Vorhees et al, 1997).…”

“…Passive sampling devices (PSDs) have been increasingly used to assess dissolved water and vapor phase air concentrations, and more recently flux (Allan et al, 2012; Allan et al, 2011; Anderson et al, 2008; Bartkow et al, 2004; Khairy and Lohmann, 2012; Matzke et al, 2012; Tidwell et al, 2016). PSDs are especially well-suited for flux assessments because they sequester the freely dissolved and the vapor phase fractions of contaminants in the water and air (Tidwell et al, 2016).…”

“…PSDs are especially well-suited for flux assessments because they sequester the freely dissolved and the vapor phase fractions of contaminants in the water and air (Tidwell et al, 2016). PSDs are not susceptible to the bias from particulates that afflict active sampling approaches.…”

“…In each of these instances the direction of flux was calculated, but neither the rate of exchange nor the rate of mass transfer was determined (Lohmann et al, 2011; Morgan and Lohmann, 2008; Prest et al, 1995). Only two previous studies have used PSDs for quantitative assessment of diffusive flux of PAHs (McDonough et al, 2014; Tidwell et al, 2016). The limited number of quantitative studies assessing flux using PSDs shows that this application of an established technology is still in its infancy, and requires further demonstration and testing.…”