Background/Objectives: Dozens of research efforts in the previous 10+ years have demonstrated that measurements made using Passive Sampling Devices (PSDs) represent precise and accurate estimates of available organic compounds in aquatic sediment, surface water, and soil. To overcome the challenges of impractical PSD deployment times in environmental matrices, the PSD research community has adopted the use of Performance Reference Compounds (PRCs) that are loaded into PSDs prior to deployment and used to infer the fraction of steady state attained during the deployment.Traditional PRCs have included compounds with a similar hydrophobicity to the compounds of interest such as stable isotope‐labeled or deuterated forms of the compounds of interest or compounds that are not expected to be absorbed in significant amounts (e.g., rare Polychlorinated Biphenyl (PCB) congeners). Adding these traditional PRCs to PSDs is expensive and requires complicated and time-consuming PRC measurement techniques (e.g., GC or HPLC methods). This presentation will highlight the application of a potentially more time- and cost-efficient suite of compounds for PRCs: visibly-detectable dye compounds. Compared to compounds traditionally used as PRCs, dyes are orders of magnitude less expensive, generally less toxic, can be added and extracted from PSDs in amounts easily measured via Ultraviolent/Visible (UV/VIS) spectroscopy or other visible/colorimetric means, and can be observed in the PSDs with the naked eye. Measurement of dyes in PSDs can be performed with an inexpensive benchtop UV/VIS spectrophotometer via a non-destructive technique in a matter of seconds for a fraction of the cost to measure traditional PRCs.
Approach/Activities: This presentation will detail approaches and benefits of using dyes as PRCs in a commercially-available polyethylene “SP3” PSD, as well as empirical evidence demonstrating proof of concept. Several experiments with dye-loaded and PCB PRC-loaded PSDs were performed in static and mixed ex situ sediment slurry systems, and an in situ exposure was performed in surface sediment near an active pier. Kinetics of the dye and PCB PRCs were evaluated by measuring PRCs before and after exposures ranging from 14 to 28 days.
Results/Lessons Learned: Our experiments in static and mixed PSD deployments in the laboratory, as well as deployments in the field, indicate the kinetics of dye PRC desorption match those of target analytes (and traditional PRCs) such that dye PRCs can serve as replacements for traditional PRCs. For example, elimination of PCB-36 (a commonly-used rare PCB PRC) from a polyethylene sampler was compared to that of a sampler spiked with Sudan III, a dye compound with a similar hydrophobicity to that of PCB-36. Elimination rate values estimated over the 14-day exposure in surface sediment at a field site were within a 25% difference (0.043 and 0.032 day-1, for PCB-36 and Sudan III, respectively), indicating agreement between the elimination rates and the acceptability of Sudan III dye as a potential PRC replacement. In contrast to PCB analysis, which requires several hours per sample, results for Sudan III can be quantified almost immediately after device retrieval via a benchtop UV/VIS spectrophotometer. Overall, the use of dye PRCs show promise as a much more streamlined and efficient approach for PSD research and development and will also enable more cost-effective analytical chemistry techniques.