Abstract
Regulations for fuel usage in maritime traffic by MARPOL are setting global standards that aims at reducing air pollution, reducing carbon emissions, and increasing energy efficiency. However, in the event of an accidental acute spill, how does conventional fuel oils compare to green ammonia in terms of potential environmental impact? We explored this challenge by a combination of an experimental ecotoxicology and a modelling approach. First, we assessed the acute and sub-lethal toxicity of fuel oils and ammonia to Atlantic cod (Gadus morhua) embryos. Atlantic cod embryos were exposed for 4 days starting 3 days after hatch, and after exposure, the embryos were transferred to clean sea water until 3 days post hatch. Survival and hatching were monitored daily, and at the end of the experiment, larvae were imaged for assessing larvae morphometry and potential deformations. Second, we simulated acute spills of the fuels using the Dose-related Risk and Effects Assessment Model (DREAM) and the Oil Spill Contingency and Response model (OSCAR) to predict spreading and estimate the risk of toxicity to pelagic marine organisms. Ammonia caused acute toxicity to cod embryos; however, no indications of delayed toxicity were observed. No additional mortality was observed during the recovery period, and the surviving larvae displayed no deformations. Fish exposed to petrogenic fuel oils, however, displayed both acute toxicity as well as clear signs of deformations. DREAM and OSCAR simulations suggests that most of the ammonia reached the surface and evaporated, but some spreading of ammonia as ammonium generated a plume which displayed concentrations exceeding predicted no-effect concentrations (PNEC). Spills of marine gas oil, very low sulphur fuel oil and heavy fuel oil behaved differently. MGO, like ammonia, spread in the water column, however, substantial fractions also evaporated, biodegraded, surfaced, and reached shorelines. Most of the heavy fuel oil and very low sulphur fuel oil, however, ended up on the surface and were carried by waves and to shorelines, and very little of the mass ended up in the water column. The MGO had a lower PNEC than ammonia, so the total volumes of water containing concentrations exceeding the PNEC was higher for MGO than ammonia. For the VLSFO and HFO, insignificant volumes of water exceeded PNEC, due to the fate outcomes discussed above.
