Determination of Oil Spill Chemical Concentrations in Nearshore Matrices

ABSTRACT Marine oil spill incidents create concerns about human health risks, particularly in nearshore locations such as beaches used for recreation. To improve the timeliness of risk estimates during an oil spill, we need to expand modelling capacity for oil spill chemicals (OSCs) from predictions for chemical bulk measurements such as Total Petroleum Hydrocarbons (TPH) to predictions of individual concentrations of the more toxic Polycyclic Aromatic Hydrocarbons (PAH)s. The objective of this study is to establish a relationship for TPH and PAH nearshore sampling concentration values with the oil mass landing and TPH hindcast from a 3D Hydrodynamic Fate and Transport Model (3D-FTM) for a past oil spill. The overall goal is to use this information to expand current modeling capacities to predict concentration distributions for individual PAHs as a starting point for health risk assessment. During Phase I of this study, historic sampling data for various matrices (weathered oil, seawater and sediments) were used to evaluate PAH concentration distributions within time-space specific categories. The categories corresponded to samples collected prior to nearshore oiling, post nearshore oiling and at no time impacted by oil as predicted by historic oil spill trajectories. For matrices within each category, concentration frequency distributions and concentration patterns were generated for a subset of PAHs. Results show differences in PAH concentration patterns within each matrix and for each category. Concentration frequency distributions for most PAHs in each category were log-normally distributed. Phase II is ongoing. Here we analyze PAH and TPH concentrations measured from surface weathered oil slick samples collected at the time of the Deepwater Horizon (DWH) oil spill. Preliminary results show that concentrations for a subset of PAHs in weathered oil slicks correlate well with TPH concentrations (R2=0.76). We are collocating the historic environmental sampling data with the output from the Oil-Connectivity Modelling System (Oil-CMS). The relationship between measured and model predicted TPH is explored by comparing values for samples that coincide in time and space with the model's particles. A subsequent step is to use output of the oil-CMS in combination with the physical and chemical properties for each PAH to predict concentration distributions for individual PAHs. The overarching goal is to improve risk estimates and, therefore, better guide public health decision-making.