Interspecific Differences in the Effects on Embryos Between Freshwater and Marine Fish Exposed to Water‐Accommodated Fractions Derived From Very‐Low Sulfur Fuel Oil

This study evaluated the toxic effects of water-accommodated fractions (WAFs) of very-low sulfur fuel oil (VLSFO) on freshwater and marine fish embryos. Embryos of Japanese medaka (Oryzias latipes), Java medaka (Oryzias javanicus), and grass puffer (Takifugu alboplumbeus) were exposed to various concentrations of VLSFO-WAF, and the effects on key parameters, such as hatching rate, hatching days, mortality, and malformations, were examined. Exposure of Japanese medaka to 50% WAF significantly reduced hatching rates and increased mortality and malformation rates. Similarly, Java medaka exhibited severe lethality, malformations, and shortened hatching days at 50% WAF. In grass puffer, exposure to 50% WAF caused a sharp increase in post-hatch mortality and malformation rates, although hatching rates remained largely unaffected. The median lethal and median effective concentrations (LC50 and EC50) were 34.8% and 15.6% WAFs for Japanese medaka; 21.3% and 8.8% for Java medaka; and 21.3% and 9.7% for grass puffer, respectively. These WAF-based toxicity endpoints were estimated from quantitatively measured chemical concentrations in the VLSFO and its WAFs: LC50 values of 41.9-68.6 μg/L for ΣPAHs and 213.2-348.3 μg/L for Σalkylated PAHs; and EC50 of 17.3-30.7 μg/L for ΣPAHs and 88.1-156.2 μg/L for Σalkylated PAHs, respectively. This study suggests that polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs present in VLSFO and its WAF strongly contribute to the observed toxicity. Additionally, VLSFO contains lower concentrations of PAHs than conventional heavy-fuel oils, although it is harmful to certain fish species.