Bioconcentration, biotransformation, and transcriptomic impact of the UV-filter 4-MBC in the manila clam Ruditapes philippinarum.

Ultraviolet filters (UV-filters) are compounds extensively used in personal care products. These compounds are produced at increasing rates and discharged into marine ecosystems in unknown quantities and with no regulation, making them emerging contaminants. Among those, the UV-filter 4-Methylbenzylidene camphor (4-MBC) is used in a variety of personal care products such as sunscreens, soaps, or lipsticks. This high consumption has resulted in its presence in various environmental matrices at in concentrations ranging from ng to µg L-1. Very little is known, however, about the possible adverse effects in exposed non-target organisms. Our study presents novel data on the bioconcentration, toxicokinetics, and molecular effects of 4-MBC in a marine bivalve species of commercial interest, Ruditapes philippinarum (Manila clam). Organisms were exposed at two different concentrations (1.34 and 10.79 µg L-1) of 4-MBC for 7 days, followed by a 3-day depuration period (clean sea waters). Bioconcentration factors (BCF) were 3562 and 2229 L kg-1 for the low and high exposure concentrations, respectively, making this pollutant bioaccumulative according to REACH criteria. Up to six 4-MBC biotransformation products (BTPs)were identified, 2 of them for the first time. Transcriptomic analysis revealed between 658 and 1310 differently expressed genes (DEGs) after 4-MBC exposure. Functional and enrichment analysis of the DEGs showed the activation of the detoxification pathway to metabolize and excrete the bioconcentrated 4-MBC, which also involved energy depletion and caused an impact on the metabolism of carbohydrates and lipids and in the oxidative phosphorylation pathways. Oxidative stress and immune response were also evidenced through the activation of cathepsins and the complement system. Such elucidation of the mode of action of a ubiquitous pollutant such as 4-MBC at the molecular level is valuable both from an environmental point of view and for the sustainable production of Manila clam, one of the most cultivated mollusk species worldwide.

Stress under the sun: Effects of exposure to low concentrations of UV-filter 4- methylbenzylidene camphor (4-MBC) in a marine bivalve filter feeder, the Manila clam Ruditapes philippinarum.

UV filters are a class of emerging contaminants with an annual estimated production of 10,000 tons worldwide that continuously enter aquatic environments. Among UV filters, 4-methylbenzylidenecamphor (4-MBC) is an organic camphor derivative used in the cosmetic industry for its ability to protect the skin against UV, specifically UV B radiation. Individuals of the Japanese clam, Ruditapes philippinarum, were exposed to 4-MBC at environmentally relevant and slightly higher concentrations (nominal: 0, 1, 10, 100 µg L-1) using a semi-static exposure system over a 7-days period followed by a 3-days depuration period (total 10 days) where no 4-MBC was added to the tanks. Assessed mortality reached up to 100 % at the highest exposure concentration and a LC50 value of 7.71 µg·L-14-MBC was derived. Environmental risk assessment carried out in a site specific environment, the Cadiz bay in the south of Spain, revealed a potential risk produced by the presence of 4-MBC. Digestive glands tissues were analysed for differential expression of genes encoding proteins involved in the stress response (SOD, MT, GST, EIF1, BCL2, TP53, CAT, 18S, GADPH, GPX, GADD45, THIO9) by RT-qPCR for relative quantification. Results showed that the presence of 4-MBC at environmentally relevant concentrations induced the expression of genes that encode for antioxidant enzymes (GST) and for proteins related to the inhibition of apoptosis (BCL2) and cellular stress (GADD), suggesting a physiological stress response.