Air-water exchange and trends of persistent bioaccumulative toxics (PBTs) across Lake Superior

Zoe Ruge, University of Rhode Island


Persistent bioaccumulative toxics (PBTs) have long been studied in Lake Superior air, water, sediment, and biota, however, sampling has often been constrained to a few study sites. Polyethylene passive samplers (PEs) provide the ability to collect time-averaged, tandem air and water measurements from any accessible point along the shore or in open water. PEs were deployed in the air and water at 19 sites across Lake Superior from June-October 2011. Samples were solvent extracted and analyzed using gas chromatography/tandem-mass spectroscopy to quantify 22 polycyclic aromatic hydrocarbons (PAHs), 11 polybrominated diphenyl ethers (PBDEs), 24 organochlorine pesticides (OCPs), and 18 polychlorinated biphenyls (PCBs). ^ PAHs are still emitted to the atmosphere from both anthropogenic activity and natural sources, and flux rates suggest net deposition into Lake Superior from the atmosphere. They were found at most sites, however, distributions appear to be associated with populated and industrialized areas (air and water ranges below detection, bd, to 190 ng/m3 and bd-130 ng/L, respectively). Retene, a signal of conifer trees and used as an indicator of forest fires, was present across the lake, representing a large portion of total PAH concentrations at rural areas, particularly in the water. PBDEs were similarly connected to developed areas, but were present at much lower concentrations (air and water range bd-19 pg/m3 and 0.051-7.6 pg/L, respectively). PBDE flux rates were dominated by BDE-47, however, flux direction was not consistent across the lake and deployment periods . PCB concentrations were also greatest near developed areas (up to 57 pg/m3 in Ontonagon air and 45 pg/L in Sault Saint Marie water), but a ban on direct emissions since the 1970s has resulted in upward flux rates. This net volatilization suggests Lake Superior is acting as a secondary source of these compounds to the atmosphere. OCPs varied greatly between individual compounds, but were overall detected at every site across Lake Superior. Long-banned hexachlorobenzene (range bd-180 pg/m3) and &agr;-hexachlorocyclohexane (bd-640 pg/L) dominated the air and water concentrations, respectively. Both exhibited fluxes indicative of near-equilibrium or net volatilization. Conversely, recently-used endosulfan I had negative flux rates across the lake due to ongoing terrestrial emissions. ^ Continuing deposition trends of currently used PBTs, changes in recently-banned PBTs, and possible secondary emissions of long-banned PBTs must continue to be monitored across Lake Superior and the other Great Lakes in order to evaluate the efficacy of regulatory measures and threats to human and environmental health. PEs provide an easy and affordable alternative to active sampling ideal for high resolution sampling of large regions, such as Lake Superior. ^

Subject Area

Chemical Oceanography

Recommended Citation

Zoe Ruge, "Air-water exchange and trends of persistent bioaccumulative toxics (PBTs) across Lake Superior" (2013). Dissertations and Master's Theses (Campus Access). Paper AAI1549143.