North sea produced water PAH exposure and uptake in early life stages of Atlantic Cod

Produced water discharges from offshore oil and gas platforms represent a significant source of petroleum components such as polycyclic aromatic hydrocarbons (PAHs) released to the ocean. High molecular weight PAHs are persistent in the environment and have a potential for bioaccumulation, and the investigation of their fate and uptake pathways in marine life are relevant when assessing environmental risk of produced water discharges. To study the exposure and uptake of 2-5 ring PAHs in early life stages of Atlantic Cod in the North Sea, we run a coupled fate and individual-based numerical model that includes discharges from 26 platforms. We consider 26 different PAH components in produced water which biodegrade with primary degradation rates; intermediate degradation products are not included. Model simulations are run covering multiple years (2009-2012) to study annual exposure variability, while a one-day time slice of spawning products from the peak spawning season are followed. By covering multiple release points and large spatio-temporal scales, we show how individuals can be exposed to produced water from multiple regions in the North Sea. We find that a combination of oceanic fate processes and toxicokinetics lead to markedly different compositions in the predicted internal concentrations of PAHs compared to discharge concentrations; for instance, naphthalene makes up 30% of the total discharged PAHs, but contributes to at most 1% of internal concentrations. In all simulations we find the predicted total internal PAH concentration (26 components) to be below 1.2 nmol/g, a factor of 1000 less than concentrations commonly associated with acute narcotic effects.