Sunscreens in Coastal Ecosystems

Since ancient times, humans have felt the need to protect their skin from the harmful effects of the sun: first with the use of vegetable oils or mud that were applied on the skin and then with the wearing of clothes, hats, or umbrellas. Today, the use of sunscreens around the world has become widespread. It has been shown that the use of these cosmetics can release large quantities of chemicals into coastal waters, either directly through bathing or indirectly through waste water treatment plants and atmospheric depositions. Due to the nature of the active ingredients of sunscreens, organic and inorganic UV filters, it has been proven that they can bioaccumulate and bioconcentrate in sediments and biota and can enter the food chain, being a problem whose true magnitude is still unknown.

Sunscreens are regulated in different ways in the world; this chapter will outline how sunscreens are limited or allowed. Limits on the use are also the key to understand the environmental origin of these ingredients and may help to understand and compare results from different areas in the world.

The occurrence of UV filters (UVFs) in the marine environment is currently one of the major concerns modern society face because it is inevitably connected with tourism, and, for many countries, the tourism industry is the major driver to the economy. We currently know that several UVFs exert irreparable damage on coastal ecosystems and that the occurrence patter is diverse as a consequence of the different regulations and legislation in every single country and the consumer’s preferences. Anyhow, the use of products containing UVFs is expected to increase because of the increase in population and life expectancy, increase of tourism industry, and the increased use by people to protect themselves from the chronic and acute effects of the increasing percentage of UV sunlight that reach the Earth.

In this chapter, the analytical strategies to determine the occurrence of organic UV filters in marine waters are presented and discussed. An overview of the environmental levels reported worldwide is also included.

UV filters are released into the coastal areas by a combination of different sources, including wastewater discharges and direct input related to recreational activities. To fully understand the risks associated with the occurrence of UV filters in the marine environment, better knowledge on their distribution and environmental behavior is required. So far, concentrations of several parts per trillion have been reported in different marine settings from touristic areas. Temporal variations in levels for organic UV filters have been associated with beach use, whereas for inorganic UV filters a preferential accumulation in the surface microlayer was observed. The latter are often released as nanoparticles, which have a tendency to form aggregates and precipitate. Due to their relatively high hydrophobicity, organic UV filters can also end up in the seafloor. Although sediments are not so frequently monitored at seawater, higher UV-filter levels (a few ng g⁻¹) are usually found. Regarding their reactivity in the marine environment, the elucidation of degradation pathways and kinetics is still mostly unknown, although photochemical degradation seems to be a major transformation route for most organic UV filters. Regarding inorganic UV filters, their nanoparticles are subjected to weathering or aging and have also tendency to generate free radicals such as hydrogen peroxide under solar irradiation.

UV-filters are of emerging concern and their toxicity has been demonstrated in many papers. Organic and mineral UV-filters are active ingredients found in sunscreens. Due to the presence of UV-filters in marine waters, studies on these compounds bioaccumulating in organisms have been carried out, and this has been complemented by toxicity studies, with reports of detrimental effects to a variety of organisms. This chapter gives an overview of the bioaccumulation and the toxicity of sunscreen UV-filters on marine species. The toxicity of both inorganic and organic UV-filters is summarized as well as their bioaccumulation in marine biota. Ecotoxicological effects of UV-filters suffer from a lack of standardization across studies. We highlighted the difficulties to make comparisons between studies and emphasize a need for harmonization.

The Mediterranean Sea, which is considered a biodiversity hotspot, is, by far, the leading tourism destination in the world, receiving more than 267 million international tourists in 2017, and producing a high anthropogenic pressure on its natural environment. The arrival of these tourists is mainly concentrated during the summer season when the use of sunscreen is higher among population. This chapter addressed the potential impact that the use and dumping of sunscreen components has in the Mediterranean Sea and the toxic effects of these components on its local marine biota (e.g. Paracentrotus lividus and Mytilus galloprovincialis), highlighting the lack of information on emblematic endangered species such as the seagrass Posidonia oceanica.

The sunscreens are complex products for protecting the skin of UV radiation. These products contain active ingredients organic and inorganic UV filters. The release of some of these components can provoke negative effects to aquatic ecosystems. The UV filters have shown to be present in environmental compartments (freshwater, wastewater, groundwater, seawater, sediment, and sand) and to be ubiquitous, motivated by the use in other applications. To assess the environmental risk of these products implies to know exposure conditions and toxic effects in order to establish the risk quotient. This is calculated as the ratio between predicted environmental concentration (PEC) or measured environmental concentration (MEC) and predicted no-effect concentration (PNEC). The organic compounds that presented higher risk were benzophenone-3, ethylhexyl methoxycinnamate, and 4-methylbenzylidene camphor. Nevertheless, this risk is depending on the location and environmental compartment. The lack of a database concentration of inorganic nanoparticles (TiO₂ and ZnO) makes difficult to carry out a realistic assessment of environmental risk, although using modeled data an approach was carried out. The results evidenced that certain risk can be related to the release of these nanomaterials from sunscreens, although a refinement will be necessary to reduce the uncertainties. Finally, some gaps of information have been identified in order to get a more realistic environmental risk assessment. Thus, the toxicity of the mixture of sunscreens compounds under realistic conditions and the improvement of the knowledge of their mode of actions could be the next steps.

The light and warmth of the sun are among the key parameters for the development of many higher life forms on Earth. As light intensity changes within seasons, organisms including mankind have evolved measures to regulate especially UV light intensity to the skin by additional pigmentation, hair, or even feathers. Nowadays, due to increased UV light intensity, change of human movement pattern, and leisure activities, additional sun protection is required. Besides clothes, sunscreen formulations are used to protect human skin from both UV A and UV B radiation. In modern sunscreens, the majority of UV filters are based on organic substances. Aromatic ring structures, high octanol, and low water solubility as well as appropriate chemical stability are needed to meet the criteria of high UV absorbance, sufficient oil solubility, and photostability during the application phase of the sunscreen product. Although naturally occurring substances may provide similar UV absorbance, the lack of chemical stability typically prevents them from being used in such cosmetic products. The high log Pow (typically in the range of 3–6) implies that these substances may accumulate in organisms and thus may cause a threat to top predators. Existing experimentally derived data on various UV filters demonstrate that the bioaccumulation potential remains clearly below critical thresholds (i.e., bioconcentration factor (BCF) is <2,000 and biomagnification factor (BMF) is <1). Due to the direct environmental release of sunscreen products and their UV filters into lakes, rivers, and coastal areas and the overall good environmental stability, chronic aquatic studies are needed to evaluate the substance intrinsic toxicity on various trophic aquatic levels. This is already reflected by the existing European chemical legislation (Registration, Evaluation, Authorisation and Restriction of Chemicals, REACH), which recommends long-term toxicity tests instead of short-term for poorly degradable and poorly water-soluble substances. Furthermore, this regulation also takes into account that additional environmental compartments may be impacted by such type of chemicals and thus requires additional data on soil- and sediment-dwelling organisms at a higher tonnage level.

However, besides all given environmental awareness to UV filters in sunscreen products, human and thus consumer safety remains as highest priority. By saying this, in the EU every UV filter used as cosmetic ingredient requires approval by the Scientific Committee on Consumer Safety (SCCS). For the human safety assessment, appropriate information on higher-tier endpoints such as repeated dose toxicity or reproduction toxicity is mandatory in case of significant systemic uptake. However, in contrast to lower-tier tests (such as eye irritation or dermal toxicity), those complex studies cannot be replaced by available in vitro or in silico methods at this time. On the other hand, the existing animal testing ban hinders industry to develop innovative new UV filters since SCCS approval will not be granted due to the lack of relevant data for the safety assessment.