Evidence of the return of past pollution in the ocean: A model study

Abstract

Chemical contamination by persistent organic pollutants (POPs) is one of the anthropogenic stressors for the deep sea. Here we use a coupled multi‐compartment chemistry‐transport model to simulate long‐term transports and fate of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT). We show that the pollution signal received by the surface waters through atmospheric deposition is propagating downward and that ocean currents can act as a secondary source of POPs. Besides considerable time lags with respect to the year of peak emission, we find in some areas, e.g., in the western and eastern North Atlantic temporal bimodal exposure toward the pollutants of mid‐level and deep waters (200–1500 m). This is caused by vertical and horizontal transport through advection diffusion and particle sinking. We suggest that the combination of the same processes will lead to a re‐rise of exposure in other sea regions in the future, including where deep‐sea fisheries take place.

A Global 3‐D Ocean Model for PCBs: Benchmark Compounds for Understanding the Impacts of Global Change on Neutral Persistent Organic Pollutants

“…Prior work suggests that accumulation of persistent organic contaminants in the subsurface ocean may provide an ongoing source to the surface ocean and atmosphere after elimination of primary emissions sources (Hung et al, ; Stemmler & Lammel, ). These studies have proposed that the ocean could act as source rather than sink for some legacy POPs due to mixing, seasonal entrainment of the mixed layer, and diffusion of volatile chemicals back to the surface ocean, followed by evasion to the atmosphere (Lohmann et al, ; Nizzetto et al, ; Stemmler & Lammel, ). Such processes have been proposed as one explanation for slowing declines in atmospheric concentrations of PCBs and even increases at some Arctic monitoring stations (Gioia, Lohmann, et al, ; Hung et al, ).…”

Organochlorine pesticides and polychlorinated biphenyls along an east-to-west gradient in subtropical North Atlantic surface water

“…They have hardly been primarily emitted since several decades, but their concentrations may be sustained by secondary emissions from oceans and land surfaces (Lammel and Stemmler 2012 ), only slowly decreasing in the global oceans (Lohmann et al 2007 ). Their concentrations might even re-rise in the deep sea (Stemmler and Lammel 2013 ). Decreasing concentrations in surface waters may be in response to decreasing atmospheric levels as was observed and predicted for the insecticides hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) (Jantunen and Bidleman 1998 ; Stemmler and Lammel 2009 ), or reflecting vertical transports in the ocean (Lohmann et al 2007 ; Nizzetto et al 2010 ).…”

On the formulation of environmental fugacity models and their numerical solutions

“…An important example is a substantial mismatch between different methods of calculating the mass of POP. This can lead to further errors in calculating interphase diffusive fluxes, which are important for studying the future distribution of POPs in a changing climate . For model developers who use fugacity as the state‐variable, checking that the difference between the mass calculated using the mass balance equations, and the mass calculated using M = fZV provides an extremely useful consistency check for their code.…”