Assessment of the Biological Response of the Scleractinian Coral Seriatopora Hystrix to Sunscreen Products

Every second, 0.8 litres of sunscreen enters ocean waters, which corresponds to the release of 25.000 tons per year. UV filters may present substantial threats to marine fauna and flora and have an impact similar to that of other contaminants. Coral reefs play a major role in marine biodiversity, and some publications suggest that they are threatened by the release of sunscreen into the environment, which should cause bleaching. The aim of this study was to evaluate the potential impact of sunscreen products on hard corals. Laboratory experiments in which Seriatopora hystrix coral fragments were exposed to 9 sunscreens at concentrations up to 100 mg/L for 96 hours were conducted, and the biological responses of the fragments were assessed. The examined parameters were coral bleaching and polyp retraction. The results obtained revealed that the 9 tested sunscreens had no effects on S. hystrix , with a recorded NOEC (No Journal of Environmental Science and Public Health which are on the order of µg/L or ng/L. Under the conditions in this experiment, the absence of toxic effects from the tested sunscreens allows us to argue the absence of potential danger on corals.


Introduction
Coral reefs play a major role in marine biodiversity, as they represent a living habitat for many marine species; therefore, the preservation of coral reefs has been a very important environmental problem in recent decades, as massive coral bleaching, which leads to the loss of symbiotic zooxanthellae hosted within scleractinian corals, has been observed and its extent has expanded quickly [1]. The causes of this phenomenon are diverse, such as excess UV radiation, temperature variation, increasing bacterial pathogens and pollutants [2]. Human activities have a strong impact on oceans and, by extension, on coral reefs, through global warming and ocean acidification, and on a more local scale, urbanization, fishing, pollution and tourism [3]. Among the many supposed threats to marine ecosystems is the use of personal care products.
The consumption of skincare and suncare products is increasing worldwide in association with the expansion of tourism in marine coastal areas. It is estimated that every second, 0.8 litres of suncare product are released into ocean waters [4]. According to previous publications, the UV filters they contain may represent substantial threats to underwater flora and fauna, and the residues of sunscreen products affect all marine ecosystems. Numerous studies have shown that some sunscreen products have hormonal effects that affect the fertility and reproduction of fish [5][6][7][8][9]. These products also impact the activities of marine microorganisms and increase the abundance of viruses present in the water [10]. Sunscreen products, of which 4.000 tons per year are absorbed by coral beds, threaten more than 10% of reefs, and by extension, disturb the biodiversity in all marine ecosystems [11].
In this context, it is essential for the cosmetics industry to develop environmentally friendly products by reducing or eliminating the use of certain controversial ingredients and/or by controlling the effects of products on the marine environment to ensure their environmental safety. This study aims to assess the potential impacts of sunscreen products on the biology of hard corals. Biological studies were conducted by exposing fragments of the coral S. hystrix to different concentrations of sunscreens and assessing its biological responses to identify potential harmful effects.

Sunscreens assessed
The present study covers 9 sunscreen products produced by the Grupo Boticário (Table 1).

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in a laboratory; therefore, no products were released into the environment to conduct the study.

Test medium
For the whole study, the test medium was artificial seawater prepared from high-purity salts added to ultrapure water, ensuring full dissolution between each salt in the following order and proportions: NaF, and 35‰ and dissolved oxygen content greater than 80%.

Choice of the tested concentrations
The test solutions were prepared by using the water accommodation fraction (WAF) method, which is suitable for products that are insoluble or partially soluble in water. The principle of this preparation method is to add a certain amount (called the "loading rate") of the tested product directly to the test medium and mix it in a closed flask with orbital shaking for 24 hours at 110 rpm at 20° +/-2°C.
The aqueous fraction of each loading charge is then recuperated. For this study, the tested loading rates for each sunscreen were 100, 56, 32, 18, 10, 5.6 and 3.2 mg/L.
The maximum loading rate corresponds to the maximum concentration (100 mg/L) used in the OECD guidelines for ecotoxicological testing [13,14] for the CLP classification. The chosen concentrations are much higher than those found in the natural environment for chemicals that come into contact with organisms. Bibliographic data indicate that the concentrations of the main UV filters from sunscreen products that enter coastal waters and other aqueous media is in the range of µg/L or ng/L [15,16]. The absence of an effect or the observation of a small effect under the conditions in this study, which were "extreme" compared to those in the natural environment, would suggest a lack of danger from the product on the tested organisms and studied parameters.

Toxicity bioassay
Coral fragments were picked up by the purchaser. On arrival at the laboratory, they were placed in aquariums containing artificial seawater. The fragments were left in the aquariums to allow them to recover from possible stress related to transport or water change. Recovery was determined on the basis of reblooming polyps (after 2 or 3 hours

Results and Discussion
Corals are home to 25% of the world's underwater Bleaching is a response of corals to external stressors, such as temperature variations, overexposure to light or exposure to chemicals [18][19][20]. This phenomenon marks the rupture of the symbiosis between the corals and algae, with the partial or total loss of zooxanthellae populations and/or the degradation of the pigments responsible for coral colour within these algae [21][22]. Without symbiotic algae, corals are more vulnerable and do not have a source of energy.
If a disturbance is not too intense and/or is not sustained over time, bleaching can be reversed, and corals can re-establish their symbiosis with zooxanthellae. Conversely, if the suffered effect is too strong, the coral dies [23]. Evaluating the effects of chemicals, particularly sunscreen products, on the environment has been a major concern in recent decades. The protection of humans against UV

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radiation is necessary; however, the use of sunscreen products, which are released into the environment, represents a real threat to ecosystems, especially marine ecosystems and coral reefs. Indeed, due to their lipophilic nature [24], sunscreen products tend to accumulate along the food chain and form a film on the water surface [25]; because of their UV filter, sunscreen products prevent the penetration of solar radiation necessary for underwater life [26]. There are two types of UV filters used in sunscreen products: mineral UV filters and organic UV filters. The use of certain organic filters, such as octocrylene, oxybenzone, and 4-methylbenzylidene camphor, is subject to much controversy, as these filters can represent a danger to the environment [16,27]. It has been demonstrated that these products can cause hormonal effects that affect the fertility and reproduction of fish [8,9]. They also impact the activities of marine microorganisms and increase the abundance of viruses present in water [11].
As a result of this growing problem, a few countries have banned some of these organic filters to preserve the environment [28]. In this context and considering the demonstrated or suspected harmful effects of some organic filters, the use of mineral filters, i.e., titanium dioxide (TiO2) or zinc oxide (ZnO), is developing in the cosmetics industry. Applying ecolabels to suncare products with mineral filters tends to promote their use, and these filters are reputed to be safer for the marine environment based on their larger particle size and lower solubility in seawater [29,30]. However, there are studies that did not conclude that these mineral filters, tested individually, are harmless to marine organisms such as green algae, corals or crustaceans [31][32][33]. Given  Table 2 and

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The  ingredients of sunscreen products to be assessed and enable the prediction of the potential threat from a product.
In our study, we were thus able to observe that the tested finished products, which contained filters in combination with other ingredients, do not have any substantial ecotoxicological effects on corals, in contrast to other finished products tested previously.
The results of this study, which was conducted under "extreme" conditions compared to those in the natural environment (i.e., at product concentrations of 100 mg/L, which is much higher than those measured in coastal waters (on the order of ng/L or µg/L), allow us to argue for the absence of potential danger from the tested products to corals.