Rebecca M. Dickhut

Polycyclic aromatic hydrocarbon (PAH) distributions and associations with organic matter in surface waters of the York River, VA Estuary

Abstract Surface water samples were collected along the salinity gradient of the York River, VA Estuary, between June 1998 and April 1999, to examine spatial and temporal variability in particulate polycyclic aromatic hydrocarbon (PAH) concentrations and their interactions with suspended particulate organic matter (POM). Specifically, relationships with source-specific lipid biomarker compounds (sterols and fatty acids) were examined to assess PAH associations with POM and to help elucidate PAH sources and modes of entry into the estuary. Principal component analysis (PCA) revealed that PAHs in the estuary can be classified into three groups: volatile, soot-associated and perylene. The three PAH groups differed in their relationships with particulate organic carbon (POC) as well as with source-specific lipid biomarkers reflecting processes controlling their delivery to the estuary. The more volatile PAHs showed a strong positive correlation with biomarkers for autochthonous (i.e. plankton-derived) POM, but only weak correlations with total POC in spring/early summer. In contrast, all PAHs except perylene were correlated with sterols of vascular plant/freshwater microalgal origin (i.e. allochthonous) during fall/winter. Perylene concentrations decreased from the head to the mouth of the estuary and were correlated with terrestrial biomarkers, suggesting that the freshwater end-member is the dominant source of perylene to this system. The varying relationships between distinct groups of PAHs and lipid biomarkers indicate that very specific pools of POM play an important role in the fate and transport of hydrophobic organic contaminants.

Atmospheric washout of polycyclic aromatic hydrocarbons in the southern chesapeake bay region.

Vapor washout of selected polycyclic aromatic hydrocarbons (PAHs), determined from discrete atmospheric and integrated precipitation samples collected every two weeks throughout 1991, was observed to be controlled by the Henrys law constant for the compound at the temperature of deposition (5-29 °C). Particle washout was found to be relatively constant for the various PAHs but to vary seasonally, with higher particle scavenging occurring in the spring and summer compared to the fall/winter. Vapor washout coefficients were negatively correlated with rainfall intensity, with stronger dependencies on precipitation rate for high molecular weight PAHs relative to low molecular weight, volatile compounds. This observation indicates that gases of the less volatile PAHs may not achieve equilibrium between air and raindrops during extremely intense precipitation events. Particle washout coefficients for PAHs were positively correlated with rainfall intensity, indicating an increased efficiency for particle scavenging from the atmosphere with precipitation rate.

Atmospheric inputs of selected polycyclic aromatic hydrocarbons and polychlorinated biphenyls to Southern Chesapeake Bay

Abstract Atmospheric and precipitation levels of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured at a rural site in southern Chesapeake Bay throughout 1991. Wet depositional inputs of PAHs and PCBs to the lower Bay were directly determined from the data; dry deposition and gas exchange fluxes were also estimated for PAHs. Notable seasonal variability in the atmospheric concentrations of aerosol-associated PAHs and gaseous PCBs was observed. Conversely, wet deposition concentrations and fluxes exhibited little temporal variability. Annual wet deposition fluxes of PAHs and PCBs were determined to vary spatially in Chesapeake Bay, presumably due to the influence of temperature on the efficiency of washout. The uncertainty in measured wet deposition and ambient atmospheric concentrations is 25–50%, however, there is currently large uncertainty associated with estimates of dry deposition and gas exchange fluxes of semivolatile organic contaminants (SOCs). Nonetheless, atmospheric fluxes of SOCs are predicted to be both into and out of lower Chesapeake Bay.

Atlantic Bluefin Tuna (Thunnus thynnus) Population Dynamics Delineated by Organochlorine Tracers

Atlantic bluefin tuna (ABFT) are highly valued and heavily exploited, and critical uncertainties regarding their population structure hinder effective management. Evidence supports the existence of two breeding populations of ABFT; a western population in the Gulf of Mexico and an eastern population in the Mediterranean Sea; both of which migrate and mix in the North Atlantic. Conventional tagging studies suggest low rates of trans-Atlantic migrations; however, electronic tagging and stable isotopes in otoliths indicate stock mixing up to 57% between management zones delineated by 45 degrees W longitude. Here we show that organochlorine pesticides and polychlorinated biphenyls (PCBs) can be used as tracers of bluefin tuna foraging grounds in the North Atlantic and confirm that stock mixing of juvenile tuna within the U.S. Mid Atlantic Bight is indeed high (33-83% eastern origin), and is likely spatially and temporally variable. We further demonstrate that >10% of the Mediterranean population is migratory, that young bluefin tuna migrate from the Mediterranean to western Atlantic foraging grounds as early as age 1, and then return to the Mediterranean Sea as young as age 5, presumably to breed. The tracer method described here provides a novel means for distinguishing bluefin tuna populations and ontogenetic shifts in migration in the North Atlantic.

Polycyclic aromatic hydrocarbon (PAH) source, sediment deposition patterns, and particle geochemistry as factors influencing PAH distribution coefficients in sediments of the Elizabeth River, VA, USA

Abstract Sediments and pore waters from two sites in the urbanized Elizabeth River, Virginia were sampled for levels of polycyclic aromatic hydrocarbons (PAHs). Pore water PAH concentrations were similar between Sites 1 and 2, despite sediment PAH concentrations being much greater at Site 2. Organic carbon-normalized distribution coefficients (KOC)obs for all PAHs were significantly higher at Site 2 compared to Site 1, but varied ∼2–3 orders of magnitude between the top and bottom of the core in the sediments at Site 1. PAH distribution between sediments and pore waters at Site 1 were most notably related to the bimodal sediment deposition patterns as depicted by X-radiograph depth profiles, and PAH isomer concentration ratios. Sedimentary organic carbon/nitrogen ratios, lignin-phenol concentrations, soot carbon, and particle surface area both before and after organic digestion, were also analyzed in order to assess the role of sediment geochemistry on PAH (KOC)obs. Different factors were determined to control particle surface area at each site, offering insight into explaining observed PAH distribution coefficients. At Site 1, sediment organic matter was inaccessible for digestion and perhaps PAH partitioning as well. Sorption of PAHs to mineral surfaces explains low values for PAH distribution coefficients observed in the deeper sediments in this core. At Site 2, large and invariant (KOC)obs may result from sediments comprised of particles (e.g., woody debris) infused with creosote and coated with organic matter sequestering PAHs within the particle matrix. Our results indicate there is significant heterogeneity in PAH distribution coefficients in estuarine sediments, which may be attributed to sediment deposition patterns, PAH source(s), and sediment geochemistry.

Aqueous solubilities of six polychlorinated biphenyl congeners at four temperatures.

Aqueous solubilities of six polychlorinated biphenyls (PCBs) were measured at 25/sup 0/C and three other temperatures by using a slightly modified generator column method. Solubility increased exponentially with temperature in the range 0.4-80/sup 0/C for all six PCBs investigated, as well as for biphenyl and 4-chlorobiphenyl. Enthalpies of solution for the PCBs and biphenyl were determined, ranging from 28.5 (4-chlorobiphenyl) to 66.6 kJ/mol (decachlorobiphenyl). These values can be used to interpolate solubilities in the experimental temperature ranges, with average errors of less than or equal to 10%, for all congeners except decachlorobiphenyl. The average absolute error for decachlorobiphenyl was 16%. 17 references, 2 tables.

Polycyclic aromatic hydrocarbons in a highly industrialized urban estuary: inventories and trends.

The abundance and composition of polycyclic aromatic hydrocarbons (PAHs) in sediments of the main stem and southern branch of the Elizabeth River (VA, USA), a highly industrialized urban estuary in the Chesapeake Bay (USA) watershed, were examined relative to historical and toxic effects levels. Total PAH concentrations in Elizabeth River sediments exceeded those observed in Baltimore Harbor and the Anacostia River, two other regions of concern in the Chesapeake Bay. The sigmaPAH concentrations from samples collected in the vicinity of two former wood-treatment facilities in the Elizabeth River had the highest sigmaPAH when compared to coastal and estuarine systems around the world. Using a linearized diffusion model equation, as much as 69% of the variability in channel sediment sigmaPAH distribution could be ascribed to inputs associated with former wood-treatment facilities along the southern branch of the Elizabeth River. Comparison of PAH levels measured in channel samples to data collected during the early 1980s demonstrated a general trend toward reduction in contaminant concentrations for most regions of the Elizabeth River channel; however, steady-state and increased sediment PAH concentrations in the vicinity of the former wood-treatment facilities were observed. Based on examination of the contaminant levels in Elizabeth River sediments using established sediment-quality criteria, the southern branch of the river remains a clear hazard to benthic and pelagic organisms.

Organochlorine pesticide air-water exchange and bioconcentration in krill in the Ross Sea.

Mean hexachlorobenzene (HCB) and hexachlorocyclohexane (HCH) concentrations, measured in seawater and air samples, confirmed the decline in levels of these compounds in Antarctic air and water. However, low alpha/gamma-HCH ratios in air at the beginning of the sampling period suggest a predominance of fresh lindane entering the Antarctic atmosphere during the Austral spring probably due to current use in the Southern Hemisphere. Water-air fugacity ratios demonstrate the potential for HCH gas deposition to coastal Antarctic seas, while the water-air fugacity ratios for HCB imply that volatilization does not account for the observed decrease of HCB in surface seawater. HCH concentrations found in krill samples were correlated with seawater concentrations indicative of bioconcentration of HCHs from seawater.

Aerosol-Mediated Transport and Deposition of Brominated Diphenyl Ethers to Antarctica

Brominated diphenyl ethers (BDE47, 99, 100, and 209) were measured in air, snow and sea ice throughout western Antarctica between 2001 and 2007. BDEs in Antarctic air were predominantly associated with aerosols and were low compared to those in remote regions of the northern hemisphere, except in Marguerite Bay following the fire at Rothera research station in Sept 2001, indicating that this event was a local source of BDE209 to the Antarctic environment. Aerosol BDE47/100 reflects a mixture of commercial pentaBDE products; however, BDE99/100 is suggestive of photodegradation of BDE99 during long-range atmospheric transport (LRAT) in the austral summer. BDEs in snow were lower than predicted based on snow scavenging of aerosols indicating that atmospheric deposition events may be episodic. BDE47, -99, and -100 significantly declined in Antarctic sea ice between 2001 and 2007; however, BDE209 did not decline in Antarctic sea ice over the same time period. Significant losses of BDE99 and -100 from sea ice were recorded over a 19 day period in spring 2001 demonstrating that seasonal ice processes result in the preferential loss of some BDEs. BDE47/100 and BDE99/100 in sea ice samples reflect commercial pentaBDE products, suggesting that photodegradation of BDE99 is minimal during LRAT in the austral winter.

Organochlorine Pollutants in Western Antarctic Peninsula Sediments and Benthic Deposit Feeders

Sediments and benthic deposit feeding holothurians were collected near the Palmer Long Term Ecological Research grid during the austral winter of 2008. Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were measured in Western Antarctic Peninsula continental shelf sediments, porewater, and benthic biota. Concentrations and fluxes in sediments decreased sharply away from the tip of the peninsula toward its interior. Sedimentary PCB fluxes were an order of magnitude lower than reported elsewhere, supporting the notion of a pristiner Antarctic environment. Hexa-chlorinated biphenyls dominated (40-100%) the PCB profiles in the sediments, while trichlorinated biphenyl 28 was the most abundant PCB congener in the porewater. PCB and OCP concentrations in holothurians were comparable to concentrations in other low trophic level biota in the Antarctic food web (i.e., krill). The partitioning of PCBs and OCPs between the sediments and porewater can be explained by a dual-mode model, which included both organic carbon and black carbon as partitioning media. Alternatively, a simpler one-parameter prediction assuming coal tar-like organic carbon performed equally well in explaining porewater concentrations The majorities of PCBs (63-94%) in the Western Antarctic Peninsula sediments were bound to black carbon or recalcitrant tar-like organic carbon, thereby lowering porewater concentrations. PCBs and OCPs in the holothurians were in equilibrium with those in the porewater.