Ecotoxicological benthic impacts of experimental oil-contaminated marine snow deposition

PAH residues and toxicity levels two years after an extensive oil spill on the northeast Brazilian coast

The most extensive oil spill ever recorded in tropical oceans occurred between August 2019 and March 2020, affecting approximately 3000 km of the Brazilian coast. This study assessed the chemical contamination and toxicity of sediments collected from affected reef areas during two sampling surveys conducted 17 and 24 months after the peak of oil slick inputs. Our results indicated that neither PAH levels nor measured toxicity showed a significant contribution from the spilled oil, with concentrations and biological effects indistinguishable from those in unaffected areas. Similarly, no differences were observed between seasons. Furthermore, there was no discernible relationship between sediment toxicity results and the measured PAH concentrations. Therefore, while biological responses indicated toxicity in most assessed areas, these responses are likely related to other local sources. This evidence suggests a natural oil attenuation process contributing to local environmental recovery. Nonetheless, further investigation is needed for other areas affected by oil spills.

Effects of suspended particles and dispersants on marine oil snow formation of crude oil/diesel oil

Marine oil snow (MOS) potentially forms after an oil spill. To fully understand the mechanism of its formation, we investigated the effects of suspended particles (SP) and dispersants on MOS formation of crude oil and diesel oil by laboratory experiments. In the crude oil experiment, the SP concentration of 0.2 g L-1 was more suitable for crude oil MOS formation. The addition of dispersants significantly stimulated N and TV during MS/MOS formation of SP at 0.4 g L-1 and 0.8 g L-1 concentration (p < 0.05). Without SP, the dispersants also stimulated crude oil MOS formation. Furthermore, the concentration of SP had a significantly positive effect on the reduction of the total amount of N-alkanes (p < 0.05). In the diesel oil experiment, after adding dispersants to diesel oil, the maximum N, Dm, and TV values at a SP concentration of 0.2 g L-1 were significantly higher than those at 0.4 g L-1 and 0.8 g L-1 (p < 0.05). Besides, we found that dispersants stimulated MOS formation in diesel oil at a SP concentration of 0.2 g L-1. However, the dispersants had an inhibitory effect on diesel oil MOS formation without SP. Notably, the MOS formed by diesel oil appeared white, unlike the black MOS associated with crude oil. These findings are important for the environmental impact of oil spills and elevated SP concentrations.

Deciphering the synergistic impact of elevated temperature and oil pollution on meiobenthic community structure: A benthocosm study

Meiobenthos has been considered as an excellent tool for biomonitoring assessment. Elevated temperature and oil pollution are considered as the most pervasive aspects of global environmental changes and matter of concern for contemporary society. Presently, very limited information is available about the synergistic effect of these stressors on meiobenthic community structure and tolerance potential from tropical intertidal environment. Here, we assessed their impacts on meiobenthic community by conducting a 60 days long benthocosm experiment selecting three sets of temperature (25°, 30° and 35 °C) and two sets of diesel oil (low and high) combinations. Gradual changes in their community composition were revealed discernibly with exposures to both the disturbances after 30 and 60 days of experimental period. Diversity profiles for the nematodes were less affected, but copepods showed a graded response of decreasing density with increasing dose of both the stressors. Other meiobenthic taxa such as halacarid mite, turbellaria and polycheate juveniles were adversely affected and eliminated from the treatments, howbeit abundance of ostracods, foraminiferans and bivalve settlers varied significantly. A 3-factor PERMANOVA indicated a significant effect of temperature, diesel, between their interaction and interaction among stressors and time on meiofaunal abundances. In case of free-living nematodes, temperature rise and diesel contamination synchronously led to an elimination of k-selected species like Halalaimus gracilis, H. longicaudatus, Oxystomina aesetosa and Pomponema sp. with a significant decrease in abundance of H. capitulatus and Oncholaimus sp. The r-selected species Daptonema invagiferoum, Sabatieria praedatrix, Theristus acer, Monhystera sp. and Thalassomonhystera sp. had endured even at high doses of diesel treatment in three different temperatures set up. The effects were evident in term of changes in life strategies with an increment of opportunistic species and increased trophic diversity of deposit feeders in treated sediments. Overall, elevated temperature together with diesel oil contamination were found to alter species dynamics within shallow intertidal meiobenthic communities, which might have significant Armageddon on benthic ecosystem functioning.

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

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.

Heat-Treated Micronized Polyethylene Powder for Efficient Oil/Water Separating Filters

The targeted separation of oil/water mixtures is a rapidly growing field of research, mainly due to contaminated water becoming an increasingly important environmental issue. Superhydrophobic materials are highly suited to this application; however, growing efforts are being devoted to developing applicable technologies within a range of research communities. The optimal technical solution is one that combines a high separation efficiency with a straightforward fabrication procedure at a low cost. In this report, micronized polyethylene powder has been utilized as a low-cost hydrophobic material to manufacture easy-to-fabricate filters. The effect of heating and solvent addition on the water repellence behaviour has been investigated, according to which the optimum fabrication conditions were determined. The filters show high water repellence (WCA = 154°) and efficient oil/water separation (~99%). The filters are designed to provide a readily achievable approach for the separation of oils (hydrophobic solvents) from water in a range of potential applications.

The effects of experimental oil-contaminated marine snow on meiofauna in a microcosm

During an oil spill, a marine oil snow sedimentation and flocculent accumulation (MOSSFA) event can transport oil residue to the seafloor. Microcosm experiments were used to test the effects of oil residues on meiofaunal abundance and the nematode:copepod ratio under different oil concentrations and in the presence and absence of marine snow. Total meiofaunal abundance was 1.7 times higher in the presence of snow regardless of oil concentration. The nematode:copepod ratio was 13.9 times lower in the snow treatment regardless of the oil concentration. Copepod abundance was 24.3 times higher in marine snow treatments and 4.3 times higher at the highest oil concentration. Nematode abundance was 1.7 times lower at the highest oil concentration. The result of the experiment was an enrichment effect. The lack of a toxic response in the experiments may be attributable to relatively low oil concentrations, weathering processes, and the absence of chemically dispersed oil.