Potential hazards of octinoxate (ethylhexyl methoxycinnamate) exposure in the seagrass Posidonia oceanica (L.) Delile: Experimental evidence.

Interest has risen in recent years to assess the fate and impacts of organic ultraviolet (UV) filters in aquatic environments, after being recognized as contaminants of emerging concern. Octinoxate, also known as ethylhexyl methoxycinnamate (EHMC), is among the widely used UV filters in sunscreen formulations. Its potential toxicological effects in aquatic biota have led to precautionary actions in some jurisdictions, such as restricting and even banning its presence in commercial sunscreens. However, research data is lacking for effective regulation of sunscreen ingredients in Mediterranean countries. Our study evaluated the response of the seagrass Posidonia oceanica to EHMC under a short-term experimental setup, recreating summer conditions in aquaria subjected to different environmentally relevant concentrations for the Mediterranean Sea (minimum: 30.57 ng L, intermediate: 710 ng L and maximum: 1420 ng L) and a control (no addition). Negative responses were evidenced in the physiology of P. oceanica due to EHMC exposure, with decreased gross primary production rates, loss of leaf chlorophyll content and inhibition of the overall nitrogen fixation associated with the seagrass tissues. Elevated oxidative stress biomarkers in P. oceanica under EHMC addition (i.e., catalase activity, polyphenols concentrations and alkaline phosphatase activity in leaves) reflect the activation of antioxidant defenses to counteract oxidative damages possibly induced in cellular components by the presence of the contaminant. Our results may conservatively imply the high ecological risk imposed to P. oceanica by maximum concentrations of EHMC in Mediterranean coastal waters. Moreover, they contribute as experimental evidence of the potentially detrimental effects of sunscreen pollution in a keystone species, such as P. oceanica, which is the main structural component of a priority habitat for conservation in the Mediterranean Sea, currently affected by multiple stress factors leading to its recession in recent years.