Contrasting the effects of biodegraded vs. non-biodegraded oil on blue mussels (Mytilus spp.)

Citation

Kalter V, Caballero-Solares A, Rise ML & Passow U (2025) Contrasting the effects of biodegraded vs. non-biodegraded oil on blue mussels (Mytilus spp.). SSRN. https://doi.org/10.2139/ssrn.5737185

Abstract
Oil spilled into the marine environment is subject to a number of fates, such as dilution in the water, dispersion, and weathering. Weathering, which changes the oil’s composition, can be caused by evaporation, photo-oxidation, or biodegradation by microbes. Bacteria, fungi and archaea that are able to degrade hydrocarbons exist globally in the ocean and are important contributors to the natural breakdown of released oil. Biodegradation occurs whenever oil is spilled, however, little is known about how this degradation process might change the oil’s toxicity. Therefore, we conducted a study using the blue mussel (Mytilus spp.) as a model organism to test the potential change in oil toxicity after biodegradation. We biodegraded a chemically enhanced water-accommodated fraction (CEWAF) of oil for 18 days in roller tanks and employed i) DNA damage assessment, ii) clearance rate assay, iii) condition index measurements, and iv) gene expression analyses, to assess whether exposure to biodegraded oil elicits a different response in blue mussels than non-biodegraded oil at the same concentration. We obtained mixed responses depending on the effect measures. First, a delayed negative effect on DNA integrity manifested in the mussels exposed to biodegraded oil, but not in the control or those exposed to non-biodegraded oil. Second, mussels in both oil treatments exhibited decreased clearance rate compared to the control after exposure. Third, we found that oil exposure could lead to a short-term suppression of expression of several genes, including genes relating to immune function in mussels exposed to non-biodegraded oil. Finally, no significant differences were observed in the condition index between the treatments at any sampling time point. These findings suggest that a prediction of oil toxicity after biodegradation may not be straightforward and seems to depend on the chosen endpoint. Further experiments could shed more light on the potential effects of this important weathering process.

Keywords
blue mussels; oil pollution; Biodegradation; comet assay; gene expression; clearance rate