Disclosing the Interference of Oxybenzone Exposure on Okadaic Acid Lipophilic Toxin Elimination by the Clam Donax trunculus

The clam Donax trunculus is a species of high economic value in the South of Europe, being strongly connected to the culinary traditions of some regions. Unfortunately, its capture is often interdicted due to the presence of high levels of okadaic acid (OA), a lipophilic toxin, in its edible tissues during blooms of harmful algae (HABs). In Portugal, interdiction periods of D. trunculus harvesting has been increasing in the last years, namely in the summer months. This study explores the hypothesis that the exposure of D. trunculus to water contaminants (namely a common sunscreen ingredient present in hygiene and personal care products – oxybenzone) could delay the bivalve elimination of OA, contributing to enhancing the interdiction period. In fact, in summer months, the occurrence of oxybenzone in coastal waters may increase due to the frequent application of sunscreen products by beach users. In the present work, an exposure experiment of D. trunculus to realistic levels of OA (5 μg/L) and oxybenzone (5 μg/L), by individual exposure and in combination, for 7 days was performed. Clams were sampled for the quantification of OA and oxybenzone in the edible tissues upon 3 (E3) and 7 (E7) days of exposure, and after 7 days of post-exposure (PE7), as well as for the determination of biochemical parameters related to biotransformation (GST), glutathione-related parameters (GSHt, GR, GPx) and oxidative damage (SOD, LPO). A significant increase of GPx was found in the clams exposed to the combination of OA and oxybenzone, in comparison to control organisms at E7, while no changes were found upon exposure to each compound individually. Differently, oxybenzone alone triggered a decrease of GPx in PE7. At E3 the mixture of the two compounds decreased GSHt levels. Moreover, the combination of both compounds elicited also a significant decrease of GR and an enhancement of LPO in PE7, suggesting long-lasting effects of both compounds when in combination.