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Using Performance Reference Compounds to Compare Mass Transfer Calibration Methodologies in Passive Samplers Deployed in the Water Column
Citation:
Joyce, Abigail AND R. Burgess. Using Performance Reference Compounds to Compare Mass Transfer Calibration Methodologies in Passive Samplers Deployed in the Water Column. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 37(8):2089-2097, (2018). https://doi.org/10.1002/etc.4167
Impact/Purpose:
At field sites that are very contaminated with anthropogenic pollution it is critical to monitor the contaminant’s concentrations and their biological availability to organisms (some, like fish and shellfish, that humans may consume). Passive samplers are a useful tool for monitoring contaminant concentrations at contaminated sediment sites both in the sediment and in the water column. In order to accurately measure dissolved water concentrations, the passive samplers must be at equilibrium with the surrounding aquatic environment or data must be collected to estimate sampler concentrations had they come to equilibrium. Performance reference compounds (PRCs) are the gold standard for correcting passive sampler data to reflect equilibrium conditions but several equilibrium models are available for analyzing PRC data. Having multiple equilibrium models may create confusion as to which model(s) should be used. This work presents the results of a study both validating and critically comparing available equilibrium models for PRCs and passive samplers. We found that two of the equilibrium models generate very similar estimates of concentration and also demonstrate similar variability. This study is one more step in the evolving process of making passive sampling a universally accepted tool for pollution monitoring.
Description:
Performance reference compounds (PRCs) are often added to equilibrium passive samplers prior to field deployments to provide information about thermodynamic equilibrium between the sampling environment and the passive sampler. Their popularity has resulted in several different models of varying complexity in the literature to analyze PRC results and better estimate freely dissolved concentrations (Cfree) of targeted compounds. Three equilibrium models are commonly used: a first order (FO) kinetic model, a non-linear least squares (NLS) fitting of sampling rate model, and a diffusion (DIF) model based on Fick’s law. PRC-loaded, low-density polyethylene (PE) strips of four different thicknesses were used as passives samplers to create an array of PRC results to assess how well each of the three equilibrium models performed. Samplers were deployed in the water column at three stations in New Bedford Harbor (MA, USA). These data allow Cfree comparisons to be performed in two ways: (1) comparing Cfree derived from one thickness using different models and (2) comparing Cfree derived from the same model using different thicknesses of PE. A total of 27 PCBs (log KOW ranging from 5.07 – 8.09) were measured at Cfree concentrations varying from 0.05 pg/L (PCB 206) to about 200 ng/L (PCB 28) at the most contaminated station. Relative standard deviations (RSDs) for total PCB measurements using the same thickness and varying model types range from 0.04-12% and increased with sampler thickness. RSDs for estimates using the same model and varying thickness ranged from 8 – 18%. ANOVA found the NLS and Diffusion models most frequently calculated statistically significantly similar Cfree values. Overall, the NLS and Diffusion models demonstrated consistent precision for all of the PCBs measured and generated similar Cfree values in this comparison. Environmental scientists and managers are encouraged to use these equilibrium models when calculating Cfree from passive sampling and PRC data.
URLs/Downloads:
DOI: Using Performance Reference Compounds to Compare Mass Transfer Calibration Methodologies in Passive Samplers Deployed in the Water Column
https://doi.org/10.1002/etc.4167