About one fifth of all coral reefs have died in the world in recent years. The main culprits were high water temperatures and more frequent hot water events (aka El Niños), excessive fertilization by droppings or fertilizers from the mainland, decreased light availability of microalgae and sediments in the water. But also chemical pollution, u.a. by means of UV filters made of sunscreens and other cosmetic products we are among the perpetrators. Sunscreen is needed and widely used in the age of ozone holes, increased risk of skin cancer, and longer and more frequent vacations by the sea. As well as UV filters in many body lotions, hair styling products, shampoos, rinses, skin creams, insect repellents and soaps, to protect skin and hair (or selected hair color) from the evil air. That we also need UV radiation, z. B for the production of vitamin D in the skin is another topic.
The origin of all evil
There are three types of UV radiation:
- UV-A has a wavelength of 320-400 nm and relatively low energy, but 80-90% reaches the Earth's surface. UV-A causes the formation of oxygen radicals (reactive oxygen species) in the skin, causing the three-dimensional structure of the DNA to burst, thereby damaging or killing the cells.
- UV-B (290-320 nm) is more energetic, but only about 1% of this radiation reaches the Earth's surface. The rest is blocked by the ozone layer. The part that gets into our skin penetrates the cells and is absorbed by the DNA, causing structural damage and cell damage or killing.
- In addition, there is still UV-C radiation, with wavelengths of 200-290 nm and high energy. They are completely blocked by the ozone layer of the atmosphere, which is why we, as mortals on Earth, do not have to worry about this type of radiation.
UV-A and UV-B cause mutations in the P53 gene suppressor in addition to the general structural damage of DNA mentioned above. The protein encoded by this gene plays an important role in DNA repair or programmed cell death with non-repairable DNA damage. Therefore, we should protect ourselves from UV-A and UV-B radiation. Broad spectrum sunscreens (UV-A and B protection) can reduce the number of precancerous and squamous cell carcinomas, and also protect against chronic damage to keratinized skin (actinic keratosis), which can lead to skin cancer. However, there is little evidence that sunscreen protects against basal cell carcinoma and black skin cancer (melanoma) – even if it is talked about over and over.
Like some preservatives (eg parabens), some UV filters (eg oxybenzone) have been discredited in the past because they affect the hormonal balance and / or immune system of many animals (including mammals like us). The effect is u.a. lower fertility and poorer survival. However, these substances are still used. Over the last ten years or more, more and more studies have shown that UV filters also help with coral deaths, especially along the holiday shores. On a holiday by the sea we want to enjoy the sun, the beach and the water, go swimming, diving, diving, kyte or other surfing. To do this without sunbathing or to reduce the likelihood of malignant skin changes, we apply sunblock. Most sunscreens contain several UV filters, with individual concentrations up to 10% – so that 20 UV% sunscreens can be made from UV filters, the rest are emulsifiers, stabilizers, preservatives, fragrances, etc.
If we follow the recommendations at least twice a day, apply 2 mg of sunscreen per square centimeter of skin, we use about 40 g of sunscreen per day (Otto and Anna normal people have an average of about one square meter of skin surface). According to tourism statistics, about 78 million tourists visit the coral reef vacation destination or near the coral reef for five days a year. About a quarter of the sunscreen is washed with seawater. To sum it all up, we get almost 4,000 tons of sunscreen, which ends up in the reef area every year. Then there is that part that rubs itself in the sand, rinses it in a hotel in the shower, or is absorbed into the blood through the skin and drained with urine. Even if sewage goes through a sewage treatment plant, which is not necessary in many areas with beautiful coral reefs, sunscreen enters the sea. Because these chemical compounds, which do not occur naturally, have nothing to do with the bacteria of the wastewater treatment plant, and there are no chemical filters for these organic compounds. At least not in conventional wastewater treatment plants. Therefore, a good deal of internal UV filters reach the sea through sewage and river systems. Some scientists estimate that about 15,000 tons of sunscreen are found in the coral reefs of the ocean. Or most of the 10,000 tonnes of UV filters produced worldwide each year. How many UV filters really land in the world's seas and reefs is unknown. But we know it’s more and more.
Measurements in various seas and countries have shown that UV filters can be detected in all waters, sediments and many organisms in the area of bathing and sports beaches. Depending on the substance and location, individual concentrations in seawater range from a few nanograms per liter of seawater (ng; billion grams) to several micrograms per liter (micrograms; one million grams) or even milligrams per liter (mg, thousand grams), as in the United States Virgin Islands in the Caribbean. Unfortunately, with these values we are in concentration areas that can do real damage in coral reefs.
But how does sunscreen damage corals? What do you do in these wonderful, colorful, highly complex ecosystems? Which UV filters are the worst?
UV filters are usually divided into physical and chemical agents. Chemical filters are organic compounds that absorb UV rays and convert energy into heat. Physical filters are inorganic compounds that reflect, diffuse or eventually absorb radiation. Often, physical filters appear as "good" and chemical as "bad guys". But it's not that easy.
Death by viruses
More than 10 years ago Roberto Danovaro and colleagues were featured in one of the magazines Environmental health perspectives published a study that different types of coral are already responding to low concentrations of sunscreens (10 µl / l). Within 18 to 48 hours, the exposed coral fragments released mucus consisting of symbiotic zooxanthel and coral tissue. No later than 96 hours, the coral bleaching was complete – the corals had distracted their power plants, the symbiotic algae called Zooxanthellen, and started starving. Because sunscreens contain many different substances, the group individually studied several UV filters and preservatives.
The most severe damage was caused by the preservative Butylparaben and UV filters Octinoxat, Oxybenzon and Enzacamen. Even in small doses, they initiated complete bleaching of the coral fragments. Therefore, sunscreens such as parabens, cinnamon esters such as octinoxate, benzophenone such as oxybenzone and camphor derivatives such as gentian seeds should be avoided as they damage the coral symbionts and therefore these corals themselves.
Coral bleaching is a u.a. triggered by the destruction of Zooxanthellen. Zooxanthellae ejected from the coral as part of the mucus have lost their photosynthetic pigments and membrane integrity. 30-98% of all Zooxanthellae emitted by Acropora hard corals were partially or completely damaged and appeared pale and translucent.
In a search for a mechanism of action to destroy zooksanthel, scientists have discovered a significant (up to 15x) increase in the concentration of viruses in water around sunscreen corals. Probably some or all of the zooksanthells had a latent viral infection that did not cause any problems under control conditions. The sunscreen then triggered a so-called lytic cycle in which viruses internally destroy the host cells (Zooxanthellae). However, damaged zooksanthels do not help the coral and repel. Corals can indeed pick up new zooksanthells, but they only do so when stressors no longer exist. In this case, only when the sunscreen is no longer present in water and coral tissue.
Oxybenzone causes damage to zooxanthelma viruses, especially when the experiment is being conducted in the light. In the dark, oxybenzone also destroys zooksanthelle, but as another study shows, it uses a completely different mechanism.
Death by digestion
If hard corals are exposed to the UV filter by oxybenzones in dark conditions, they will digest their symbiotic zooxanthels. Corals, like all other cnidarians, have gastrodermis, the "digestive layer of the skin." It releases the digestive enzymes and then collects the dissolved food particles by phagocytosis, further digestes them, and then distributes the nutrients to the adjacent tissue. Cells and microorganisms are normally digested, which absorb corals by filtration into their gastric space. When oxybenzone plays in the dark, they digest their vital symbionts. This process, in which symbionts are "eaten", is called symbiophagia.
The result of symbiophagy is again symbiont loss, bleaching and, with continued stress, death.
Death by ossification
Oxybenzone, like other benzophenones, also damages coral reefs by altering coral larvae. Coral larvae arise from fertilized eggs and float freely in the water in their early stages of development, forming part of plankton. After a few hours to the day, they reached the site of their development, where they settled in one place and fastened to a solid surface using calcium carbonate precipitation. If different benzophenones come into play, the free-swimming larvae deform, causing them to settle prematurely. Too early because they are not ready to develop yet and because they may not have found a suitable place to build a new coral colony.
Instead of releasing only calcium carbonate (CaCo3) due to attachment and then starting normal formation of polyps and subsequent colonies, the larvae release too much and uncontrolled CaCO3. It "ossifies": the established larva is completely enclosed by its own bonfire. Damage to coral larvae minimizes the employment and survival of juvenile corals, and thus the resuscitation of previously damaged reefs. Not only in theory, but also in Trunk Bay (Virgin Islands), where the concentration of oxybenzone (and benzophenone-2) is particularly high and no re-population of faulty reefs is observed, it is very likely that this will be the reality.
As if the direct effects of oxybenzone on corals are not bad enough, there is another problem with this UV filter. Decomposition of oxybenzone in the coral produces benzophenone-1 (BP-1) and benzophenone-8 (BP-8). They are even more damaging to coral cells than oxybenzone itself. Like oxybenzone, they create stress on corals and larvae dependent on coral species, causing bleaching and death. In some cases, DNA damage can be detected. In addition, the metabolites of oxybenzone BP-1 and BP-8 bioaccumulate more than oxybenzone, so the actual concentration in coral tissue may be higher than in free seawater. There, the two benzophenones are rather poorly concentrated. Unlike oxybenzone, its concentration in surface seawater worldwide is higher than that of other UV filters.
Death by fatty acids
Sunscreen should be waterproof as we do not want to constantly grease or lose protection with the swimmer. Therefore, sunscreens are generally fat soluble (lipophilic) and not water soluble. But it also means that they not only spread evenly in the water and must be well diluted in the vast ocean. Instead, they are stored in animals, especially in lipophilic organs: they bioaccumulate. In addition, they precipitate into sediments, which in this case, concentrations can continue to increase over time – with potentially devastating effects on soil-dwelling organisms. Concentrations of UV filters in seawater are known to range from 1-100 ng / L to several µg / L, from sediments of far higher concentrations (up to mg / L).
Particularly lipophilic is the UV filter that has now replaced oxybenzone in many sunscreens: Ococrylene. In addition, ococrylene is particularly photostable, unlike many other UV filters. In this way it is used to protect other UV filters from being destroyed by light. To show the ubiquity of this UV filter, it is contained in seven of the nine sunscreens I have at home. While in seawater average concentrations of several µg / L are measured with high seasonal fluctuations, they are much higher in sediments and especially in lipophilic tissues of marine animals. As a result, they continue to accumulate in the food chain, from bivalve molluscs to marine mammals, and so far have managed to survive in zoos. B. dolphin livers are detected.
But what actually enriches ococrylene? This has in a.a. a survey last year of Didier Stien and his colleagues. The visible, short-term effect is only at relatively high, experimental concentrations of 300 micrograms / L: the hard corals tested fed their polyps. Changes at the molecular level, however, were observed much earlier, at any concentration of ococrylene above 5 µg / L over a period of seven days: the fatty acids were bound to the ococrylene compounds, indicating a change in fatty acid metabolism in coral polyps or symbionts. The resulting ococrylene metabolites are thus even more lipophilic than the parent compound, which is why they can accumulate even more in tissues.
In addition, increased levels of carnitine were detected. Carnitine, which plays an important role in fatty acid metabolism, has been a marker of cellular toxicity and is associated with mitochondrial dysfunction. Mitochondria are responsible for supplying energy to cells, they are almost power stations. If the mitochondria do not function properly, the cell has no available energy. Which can ultimately lead to cell death.
Death by antiseptic
In many cases, organic UV filters are detrimental to corals and other marine organisms. But what about eco-friendly or skin-often-sun creams that contain mineral UV filters such as zinc oxide (ZnO) and titanium dioxide (TiO2)?
The environmental suitability of these substances largely depended on the size of the particles used. ZnO sunscreens, applied to the skin as a white layer, have relatively large particles, more than 150 nm in diameter. Because only a few of us on the beach want to appear as white zombies or clowns, the cosmetics industry cuts particles below 35 nm, so it uses so-called nanoparticles. This reduces the zombie factor but increases the toxicity.
Zinc oxide nanoparticles significantly impair the photosynthesis of zooxanthel. At concentrations actually measured in coral reef systems (100 µg / L), the photosynthetic activity of Zooxanthella declines by more than one month from exposure by more than two-thirds. This means that only a third of the common sugar compounds are available to the coral system (polyps + Zooxanthellen). Corals are starving and hunger is stress. Stressed coral polyps repel their symbiotes if they are stressed, go on hunger strike, and when they die longer, they die.
How does zinc oxide nanoparticles manage it? They work both by creating dissolved zinc ions, which produce oxygen radicals, and by physical damage in direct contact (like many other nanoparticles). Oxygen radicals trigger oxidative stress that kills cells. Exactly this effect is used by zinc oxide-containing fats, because oxygen radicals destroy bacteria, thus acting antiseptic. Therefore, we should not be surprised if ZnO acts on other unicellular organisms, such as Zooxanthellen. To limit the formation of oxygen radicals, the cosmetic industry began coating nanoparticles with silica, magnesium or aluminum. It actually helps – but it's not against another mechanism of damage to ZnO nanoparticles.
This mechanism is the mechanical damage to the lipid membrane that surrounds the cells. While oxygen radicals act primarily on zooksanthels, they are primarily coral tissues whose cell membranes are destroyed. The polyps were again exposed to acute stress. And we already know that stressed corals strike hunger (i.e., bleach).
Many sunscreens also contain mineral UV filters, such as titanium dioxide and zinc oxide, because the skin is then protected from both UV-A and UV-B radiation. Titanium dioxide seems less harmful than zinc oxide, especially since titanium nanoparticles are usually coated to prevent the formation of oxygen radicals. But because of the general problems with nanoparticles, we should also be careful here. Larger particles, on the other hand, are both effective and largely neutral UV filters.
A sunblock without death?
The U.S. sunscreen market alone was estimated at nearly $ 1 billion in 2016. The cosmetics industry will not give up on this market simply because most of the UV filters used are damaging to aquatic organisms (and us). Instead, new names and ingredients, often derivatives of substances caught in crossfire, will always be found. Fortunately, there is also research into eco-friendly alternatives, UV filters that nature itself produces. While this does not mean that they cannot be toxic (aconite from coneflowers and conotoxins from cone snails are also natural), it does mean that they can be naturally degraded. These natural UV filters include:
- Marine organisms containing, for example, cyclohexene rings having different functional groups;
- UV algae filters, eg amino acids similar to mycospirin (for my hemophile readers: e.g. palitin, 2-[[3‐amino‐5‐hydroxy‐5‐(hydroxymethyl)‐2‐methoxycyclohex‐2‐en‐1‐ylidene]amino]acetic acid and shinorin, (2S) -2-[[3‐(carboxymethylimino)‐5‐hydroxy‐5‐ (hydroxymethyl)‐2‐methoxycyclohexen‐1‐yl]amino]3-hydroxypropanoic acid)
- Gadusol (3,4,5-trihydroxy-5- (hydroxymethyl) -2-methoxycyclohex-2-en-1-one) from zebrafish (Danio rerio)
- Herbal substances such as glucolimnanthin derivatives from the North American plant genus Limnanthes, to which, for example, owned by Oregon and California belong to Douglas Marigold.
Fortunately, legislation is slowly following, for example, in Hawaii, where oxybenzone and octinoxate, found in most common sunscreens, will be banned from 2021. Not for health reasons for us, but for the protection of marine ecosystems. Definitely a step in the right direction – because if harmful UV filters are banned, the chance of new, also harmful, substances not even getting approved is increased. This would force the industry toward more environmentally friendly alternatives – and without coercion, it is unlikely to succeed.
In the US, only 16 UV filters are approved for cosmetics, in Europe and Australia almost twice as many. Unfortunately, many of the approved UV filters are harmful to the environment – it is often difficult to detect whether a sunscreen can be used with good conscience or not. Because there are many different names for each UV filter, and different substances are approved in the US, Europe and Australia. For some of the UV filters I have discussed in this text, I will add more names to the list below. So far, only the effects of some approved UV filters on the environment have been studied. It may be natural that just not tested yet are not harmless to coral reefs and other aquatic inhabitants – but until these studies have been conducted, we can assume that these substances are no more dangerous than the UV filters described above.
It won't work without sunscreen, but clothing and hats that stay in the shade and avoid direct sunlight can help reduce our environmental impact with UV-containing cosmetics, thus reducing damage to marine ecosystems, including coral reefs. There are already enough of them to fight for survival in the increasingly hot seas.
And if we don't want organic UV filters for these sensitive ecosystems, maybe we should do it ourselves: Many organic UV filters enter our blood through the skin (and through the food chain), some can cause damage to the blood-brain. Crossing the barrier, others were discovered in breast milk. However, whether they affect hormonal balance and development in humans or are neurotoxic, as in the case of various invertebrates and fish, remains to be seen.
the name of the confusion
- Oxybenzone, also known as benzophenone-3, BP-3, 2-hydroxy-4-methoxyphenyl-phenylmethanone, 2-hydroxy-4-methoxybenzophenone;
- 2-ethylhexyl ester (IUPAC) or 2-ethylhexyl-2-cyano-3,3-diphenylacrylate, OC, octocrylene, octocrylene, (RS) -2-cyano-3,3-diphenylacrylic acid;
- Octinoxate, OMC, ethylhexyl-4-methoxyquinamate, trans-octyl methoxy cinnamate, ethyl hexylmethoxy cinnamate;
- Enzacamen, 4-methylbenzylidene camphor, 4-MBC;
- Benzophenone-1, BP-1, 2,4-dihydroxybenzophenone, also benzoresorcinol
- Benzophenone-8, BP-8, dioxybenzone
Further information on the ingredients can be found in z. On this site:
Robert B. Raffa et al., 2018; J Clinical Pharmacy and Therapists: Sun bans: Coral reefs and skin cancer; Doi: 10.1111 / jcpt.12778
Roberto Danovaro et al. 2008; Environmental Perspective: Sunscreens cause coral bleaching, triggering viral infections; Doi: 10.1289 / ehp.10966
Jean-Pierre Fel et al 2019; Coral Reefs 38: Photochemical response of the scleral coral Stylophora pistillata to some sunblock ingredients; DOI: 10.1007 / s00338-018-01759-4
Tangtian He et al 2019; Total Environmental Science 651: Comparative toxicity of four benzophenone ultrasonic filters in two life stages of two coral species; Doi: 10.1016 / j.scitotenv.2018.10.148
Cinzia Corinaldesi et al 2018; Total Environmental Science 637-638: Effect of Inorganic UV Filters Contained in Sunscreen Products on Tropical Stone Corals (Acropora spp.); Doi: 10.1016 / j.scitotenv.2018.05.108
Didier Stien et al 2018; Anal. Chem: Metabolomics reveal that ococrylene accumulates in Pocillopora damicornis tissues as fatty acids and triggers coral cell mitochondrial dysfunction; Doi: 10.1021 / acs.analchem.8b04187;
Elizabeth Wood 2018; ICRI briefing: Effects of sunscreens on coral reefs; Download: https://www.icriforum.org/sites/default/files/ICRI_Sunscreen_0.pdf