Using performance reference compound-corrected polyethylene passive samplers and caged bivalves to measure hydrophobic contaminants of concern in urban coastal seawaters.

Low-density polyethylene (PE) passive samplers containing performance reference compounds (PRCs) were deployed at multiple depths in two urban coastal marine locations to estimate dissolved concentrations of hydrophobic organic contaminants (HOCs), including dichlorodiphenyltrichloroethane (DDT) and its metabolites, polychlorinated biphenyl (PCB) congeners, and polybrominated flame retardants. PE samplers pre-loaded with PRCs were deployed at the surface, mid-column, and near bottom at sites representing the nearshore continental shelf off southern California (Santa Monica Bay, USA) and a mega commercial port (Los Angeles Harbor). After correcting for fractional equilibration using PRCs, concentrations ranged up to 100 pg L(-1) for PCBs and polybrominated diphenyl ethers (PBDEs), 500 pg L(-1) for DDMU and 300 pg L(-1) for DDNU, and to 1000 pg L(-1) for p,p'-DDE. Seawater concentrations of DDTs and PCBs increased with depth, suggesting that bed sediments serve as the source of water column HOCs in Santa Monica Bay. In contrast, no discernable pattern between surface and near-bottom concentrations in Los Angeles Harbor was observed, which were also several-fold lower (DDTs: 45-300 pg L(-1), PCBs: 5-50 pg L(-1)) than those in Santa Monica Bay (DDTs: 2-1100 pg L(-1), PCBs: 2-250 pg L(-1)). Accumulation by mussels co-deployed with the PE samplers at select sites was strongly correlated with PE-estimated seawater concentrations, providing further evidence that these samplers are a viable alternative for monitoring of HOC exposure. Fractional equilibration observed with the PRCs increased with decreasing PRC molar volume indicating the importance of target compound physicochemical properties when estimating water column concentrations using passive samplers in situ.

Passive sampling methods for contaminated sediments: scientific rationale supporting use of freely dissolved concentrations.

Passive sampling methods (PSMs) allow the quantification of the freely dissolved concentration (Cfree ) of an organic contaminant even in complex matrices such as sediments. Cfree is directly related to a contaminant's chemical activity, which drives spontaneous processes including diffusive uptake into benthic organisms and exchange with the overlying water column. Consequently, Cfree provides a more relevant dose metric than total sediment concentration. Recent developments in PSMs have significantly improved our ability to reliably measure even very low levels of Cfree . Application of PSMs in sediments is preferably conducted in the equilibrium regime, where freely dissolved concentrations in the sediment are well-linked to the measured concentration in the sampler via analyte-specific partition ratios. The equilibrium condition can then be assured by measuring a time series or a single time point using passive samplers with different surface to volume ratios. Sampling in the kinetic regime is also possible and generally involves the application of performance reference compounds for the calibration. Based on previous research on hydrophobic organic contaminants, it is concluded that Cfree allows a direct assessment of 1) contaminant exchange and equilibrium status between sediment and overlying water, 2) benthic bioaccumulation, and 3) potential toxicity to benthic organisms. Thus, the use of PSMs to measure Cfree provides an improved basis for the mechanistic understanding of fate and transport processes in sediments and has the potential to significantly improve risk assessment and management of contaminated sediments.

Investigating desorption of native pyrene from sediment on minute- to month-timescales by time-gated fluorescence spectroscopy.

We investigated desorption of native pyrene from field-aged sediments using time-gated, laser-induced fluorescence (LIF) spectroscopy. LIF is superior to conventional analytical methods for the measurement of quickly changing dissolved pyrene because it allows observations at minute-scale resolution, has a low detection limit (approximately 1 ng/L), and minimizes sample loss and disturbance since it requires no system subsampling and chemical analysis. The efficacy of LIF was demonstrated in studies of pyrene desorption from Boston Harbor sediment segregated into different size-fractions (38-75, 75-106, and 180-250 microm diameter) and used in varying solid-to-water ratios (20, 70, and 280 mg(solid)/L). The effects of particle size and solid loading on desorption were consistent with diffusion physics. For suspension conditions between 20 and 280 mg(solids)/L, we observed desorption continuing toward an apparent plateau level over the course of weeks to months. This implies that the characteristic desorption time of pyrene from fine sediments and, by inference, other sediment-bound hydrophobic organic compounds (HOCs) of similar hydrophobicity, exceeds the typical characteristic times for pore water flushing and resuspension events. Consequently, the assumption of local sorption equilibrium in modeling efforts would be inappropriate.

Polyethylene devices: passive samplers for measuring dissolved hydrophobic organic compounds in aquatic environments.

We demonstrate the use of polyethylene devices (PEDs) for assessing hydrophobic organic compounds (HOCs) in aquatic environments. Like semipermeable membrane devices (SPMDs) and solid-phase microextraction (SPME), PEDs passively accumulate HOCs in proportion to their freely dissolved concentrations. Polyethylene-water partition constants (K(PEW)S) were measured in the laboratory for eight polycyclic aromatic hydrocarbons (PAHs), five polychlorinated biphenyls (PCBs), and one polychlorinated dibenzop-dioxin (PCDD), and these were found to correlate with octanol-water partition constants (K(OW)s; log K(PEW) = 1.13 log K(OW) - 0.86, R2 = 0.89). Temperature and salinity dependencies of K(PEW) values for the HOCs tested were well predicted with excess enthalpies of solution in water and Setschenow constants, respectively. We also showed that standards, impregnated in the PED before deployment, can be used to correct for incomplete equilibrations. Using PEDs, we measured phenanthrene and pyrene at ng/L concentrations and 2,2',5,5'-tetrachlorobiphenyl at pg/L concentrations in Boston Harbor seawater, consistent with our findings using traditional procedures. PEDs are cheap and robust samplers, competent to accomplish in situ, time-averaged passive sampling with fast equilibration times (approximately days) and simplified laboratory analyses.