Marine Snow Aggregates are Enriched in Polycyclic Aromatic Hydrocarbons (PAHs) in Oil Contaminated Waters: Insights from a Mesocosm Study

Abstract

Marine snow was implicated in the transport of oil to the seafloor during the Deepwater Horizon oil spill, but the exact processes remain controversial. In this study, we investigated the concentrations and distributions of the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) in marine snow aggregates collected during a mesocosm experiment. Seawater only, oil in a water accommodated fraction (WAF), and Corexit-enhanced WAF (DCEWAF) were incubated for 16 d. Both WAF and DCEWAF aggregates were enriched in heavy molecular weight PAHs but depleted in naphthalene. DCEWAF aggregates had 2.6 times more total 16 PAHs than the WAF (20.5 vs. 7.8 µg/g). Aggregates in the WAF and DCEWAF incorporated 4.4% and 19.3%, respectively of the total PAHs in the mesocosm tanks. Our results revealed that marine snow sorbed and scavenged heavy molecular weight PAHs in the water column and the application of Corexit enhanced the incorporation of PAHs into the sinking aggregates.

Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers (ADDOMEx): Toward a Synthesis of Processes and Pathways of Marine Oil Snow Formation in Determining the Fate of Hydrocarbons

“…One clear pattern that emerged from this analysis, however, is the depletion of naphthalene and fluorene in nearly all the marine snow and the sediment samples relative to the composition of the original Macondo oil and the surrogate oil used in the roller table and mesocosm experiments. This is not surprising, as studies have shown rapid depletion and degradation of water soluble, light, volatile, low-molecular weight PAHs such as naphthalene and fluorene (Kappell et al, 2014;Bacosa et al, 2020). Overall, this analysis shows that the marine snow formed in the laboratory experiments such as roller table and mesocosm experiments closely mimicked the material found to be sedimenting in the field, further underscoring the role of MOSSFA phenomena during the DwH oil spill.…”

“…A comparison of PAH composition in MOS from laboratory roller table (Genzer et al, 2020) and mesocosm experiments [Bacosa et al, 2020;and GRIIDC dataset (10.7266/ER1EGZ8E)] with the PAH composition examined in the sediment samples of Gulf of Mexico (Romero et al, 2015), revealed interesting findings (Figure 5). Using non-metric multidimensional scaling (NMDS), the data points of both WAF and DCEWAF from roller table and mesocosm experiments clustered together with the sediment samples, suggesting some level of consistency in the PAHs that tend to remain in marine snow.…”

“…There has been considerable work done over many decades to determine parameterizations of sinking velocities of marine snow (Alldredge and Gotschalk, 1998;Iversen and Lampitt, 2020; Dibenz[a,h]anthracene, and Benzo[ghi]perylene were used for the analysis, with concentrations of each PAH normalized to percentage of total PAHs in each sample. More details on the PAH extraction, sample collection, field site and design of the roller table and mesocosm studies can be found in Genzer et al (2020); Bacosa et al (2020), Romero et al (2015) and GRIIDC dataset (10.7266/ER1EGZ8E). Laurenceau-Cornec et al, 2020;and the review by Silver, 2015).…”

“…Data points clustered to the right are sample from the original Deepwater Horizon (DWH) Macondo oil and the Day 1 sample from surrogate oil used in the laboratory mesocosm and roller table studies, whereas the points clustered largely to the left are marine snow samples from the field and laboratory experiments. Only PAHs such as Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, and Benzo[ghi]perylene were used for the analysis, with concentrations of each PAH normalized to percentage of total PAHs in each sample.More details on the PAH extraction, sample collection, field site and design of the roller table and mesocosm studies can be found inGenzer et al (2020);Bacosa et al (2020),Romero et al (2015) and GRIIDC dataset (10.7266/ER1EGZ8E).…”

Technological Developments Since the Deepwater Horizon Oil Spill

“…The BRTs were used by Doyle et al (2018) in mesocosm experiments designed to study the relationship among microbial community structure, oil and Corexit, and MOS in coastal surface waters; by Bacosa et al (2020) to investigate the concentration and distribution of hydrocarbons in marine snow aggregates; and by Shi et al (2020) to determine the half-lives of individual hydrocarbons in simulated oil spill scenarios with and without dispersant.…”