Ecotoxicity of synthetic oils used in offshore wind turbines with bacteria, algae and copepods.

Offshore wind energy is expanding to support the global green energy transition, yet the environmental risks of associated chemical discharges remain unclear (Hengstmann et al., 2025). Especially, the high-performance synthetic oil present in up to 8,000 L for each offshore wind turbine (OWT).
Thus, the aim of this study is to determine the ecotoxicity of five synthetic oils (gear, lubricant, hydraulic, dielectric, and cooling oils) used in OWTs towards three regulatory-relevant marine species: Aliivibrio fischeri (bacteria), Skeletonema pseudocostatum (algae), and Acartia tonsa (copepod). The water accommodated fraction (WAF) was tested for new and spent oils. Additionally, the total organic carbon (TOC) of each oil was measured to assess their contribution to the ecotoxicological response.
Growth inhibition of algae (S. pseudocostatum) was found to be the most sensitive endpoint among the tested organisms with toxicity (EC 50 ) ranging from highest to lowest: gear oil (0.0017%) > lubricant oil (0.021%) > dielectric oil (0.19%) > hydraulic oil (0.37%) > cooling oil (1.4%). New oils were generally more toxic than their used counterparts. Besides, normalization with TOC did not show linear correlation with the ecotoxicological response of the tested oils.
These findings highlight that oils used in OWTs can pose a risk on marine organisms, with gear and lubricant oils indicating the highest toxicity levels. Further studies to address the persistency and release rate of the synthetic oils are necessary to determine the long-term environmental impact of offshore wind energy, especially given the projected expansion.