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Anti coral cream

Active substances found in sunscreens endanger corals

Noam Levithan and Yonat Ashhar Galileo

A healthy coral (left) exposed to the substances present in sunscreen preparations turns white (right) after the death of the symbiotic algae that lived inside it. Photo: Roberto Danovaro

A healthy coral (left) exposed to the substances present in sunscreen preparations turns white (right) after the death of the symbiotic algae that lived inside it. Photo: Roberto Danovaro

A study published in the journal Environmental Health Perspectives I verified the suspicion that sunscreens may cause coral reefs to bleach. Four organic compounds common in ultraviolet (UV) radiation filtering preparations cause dormant viruses, found within the endosymbiotic algae (called zooxanthellae) that live in the bodies of reef-building corals, to "wake up" and go into a lethal, lytic state. In this situation, the viruses multiply until the algae explode, and the viruses released from them into the environment may infect additional coral colonies. The algae living in the corals provide them with organic matter and energy that they produce in the process of photosynthesis, and also help in the process of depositing the calcium carbon used to build the coral skeleton. When the algae explode and are excreted from the coral, it is left white and starved, and eventually dies.

Even before the research findings were published, some popular tourist sites prohibited swimmers using "snorkels" and professional divers from using sunscreen preparations, since the operators of the sites suspected that the chemical substances found in the preparations were responsible for the increase in the mortality of corals and other living creatures at the diving sites. These chemical substances are fat soluble and therefore may accumulate in the tissues of marine animals. On top of that, some also break down in light into toxic byproducts.

To check if there is indeed a connection between sunscreen products and coral bleaching, Roberto Danovaro and his colleagues from the Polytechnic University of Marche in Ancona, Italy, collected coral samples from several tropical waters, including the Red Sea. When a tiny amount (10 microliters per liter) of sunscreen cream was added to the seawater in which the samples were grown, the virus "awakened" and the coral samples turned completely white within four days, while the control samples remained healthy and kept their color. In the examination of the sea water after the addition of the radiation filter preparation, many algae were found, which were secreted from the samples, as well as a huge amount of viruses. Since the samples were taken from different sites in the world, and yet contained the dormant virus, the researchers concluded that the virus is widespread among zooxanthellae.

Danobrow and his colleagues also tested the effect of separate components of the sunscreen preparations, and not just the entire cream, and found that each of four organic compounds is capable of causing, in very low concentrations, the bleaching of corals. The compounds are the preservative paraben and the sunscreens cinnamate, benzophenone and a derivative of camphor (methyl-benzylidene camphor). Other components of the preparations did not cause the release of viruses and the bleaching of the corals.

This study adds another factor to the list of natural and man-made factors, such as beach pollution, that endanger coral reefs. However, unlike the other risk factors, it is easy to reduce the damage caused by sunscreen products. Danobrow suggests that the swimming and diving tourists - which he says endanger about 10% of the world's coral reefs - should switch to using sunscreens that physically block and reflect the sun's radiation, such as a long shirt or preparations based on titanium dioxide.

The original article:

Danovaro, R. et al. Sunscreens cause coral bleaching by promoting viral infections. Environ. Health Perspective. 116, 441–447 (2008). doi: 10.1289/ehp.10966

The original article was published in Galileo magazine issue 115, March 2008

3 תגובות

  1. Interesting and important article.
    It's just a shame that the title isn't more informative and reminiscent of ynet titles and the like.

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