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A stochastic framework for addressing chemical partitioning and bioavailability in contaminated sediment assessment and management
Citation:
Brennan, A., Dave Mount, AND N. Johnson. A stochastic framework for addressing chemical partitioning and bioavailability in contaminated sediment assessment and management. Society of Environmental Toxicology and Chemistry (SETAC) North America, Fort Worth, NC, November 15 - 19, 2020. https://doi.org/10.23645/epacomptox.21127243
Impact/Purpose:
Presentation to the Society of Environmental Toxicology and Chemistry (SETAC) North America annual meeting November 2020
Description:
The use of passive sampling to quantify net partitioning of hydrophobic organic contaminants between porewater and sediment solid-phase has led to advancements in the ability to predict bioavailability and toxicity as well as innovative contaminant management strategies. Despite significant progress, variance in partitioning strength remains an intractable problem due to a complex mixture of phases present in natural and anthropogenic organic matter. When solid-phase concentration (Ctotal) is known but porewater measures are not available, variability in passive sampling-derived sediment-porewater partitioning (KTOC) can be used to estimate the variance in expected porewater concentrations (Cfree). We propose a stochastic framework in which an estimated range of Cfree exposure can be paired with biological effects data, providing a quantitative and transparent way of estimating the risk of Cfreeexceeding a toxic unit or tissue concentration threshold for polycylic aromatic hydrocarbons (PAHs). We apply the framework to both an individual biological endpoint or a sensitivity threshold for a biological assemblage in an ecosystem. The stochastic framework presented here uses the extent to which actual aggregated PAH partitioning to the solid-phase is greater than that predicted by default KTOC values when normalized for potency, a quantity termed the bioavailability ratio (BR). We use the BR to derive a continuous estimate for the probability that aqueous-phase potency (interstitial water toxic units) will exceed a threshold along a continuum of solid-phase contaminant quantity (equilibrium partitioning sediment benchmark toxic units). Our analysis shows the implications of the variance in BR when applied to solid-phase measurements from moderately contaminated sediments. At lower contaminant concentrations, the risk curves derived from BR distributions with large variance exceed biological thresholds at lower Ctotal compared to those with a smaller variance. By considering differences in the variance of KTOC and BR, estimates of risk posed by sediment-associated contaminants are more transparent and nuanced. Stochastic descriptions of contaminant partitioning can refine screening-level assessments using Ctotal until passive sampling is routinely incorporated into sediment assessments.
URLs/Downloads:
DOI: A stochastic framework for addressing chemical partitioning and bioavailability in contaminated sediment assessment and management
BRENNAN PLATFORM STOCHASTIC FRAMEWORK 20201104.PDF (PDF, NA pp, 1538.911 KB, about PDF)