By Michalle Kovacevic
Sydney, Australia — The chemicals in sunscreen that protect swimmers from sunburn may also be indirectly striking a deadly blow to coral reefs, a new study has found.
"Our results should be considered as a warning about the use of these chemicals and as a claim for further research to develop new eco-friendly sunscreens." said Antonio Pusceddu, marine scientist from the Polytechnic University of Marche in Italy and co-author of the study reported in the journal Environmental Health Perspectives.
Coral reefs are one of the world's most diverse ecosystems but 60 per cent are threatened by factors including climate change and pollution.
In recent decades, coral 'bleaching' has becoming a major problem. This occurs when symbiotic algae that live inside coral tissues die, thus exposing the "naked" white coral skeleton, said Pusceddu. Bleaching itself has been linked to rising temperatures, toxins and ultraviolet light.
To probe their hunch that chemicals in sunscreen might be having an effect on coral bleaching, Pusceddu and his team collected small pieces of coral from tropical reefs in the Indian, Atlantic and Pacific Oceans.
They exposed these samples to varying concentrations of sunscreen, starting at just 10 microlitres per litre of seawater. The results showed that even at these low doses the chemicals could induce the release of viruses within the corals that caused bleaching.
These chemicals - primarily parabens, cinnamates, benzophenones and camphor derivates - boosted the activity of pathogenic viruses that had otherwise lain dormant within the algae, and triggered a mass die-off, leading to bleaching.
The sunscreen resulted in the release of near 15 times more virus than in the coral not exposed to it, the researchers reported, completely bleaching the coral within 96 hours.
Some experts are yet to be persuaded by the findings, however.
"Any contaminant can experimentally damage a coral under artificially high concentrations. The amount [in the wild] must be tiny due to dilution," commented Terry Hughes, director of the Australian Research Council's Centre of Excellence for Coral Reef Studies at James Cook University in Queensland.
"Imagine how much water a tourist wearing one teaspoon of sunscreen swims through in an hour-long snorkel! Compared to real threats like global warming, runoff and overfishing, any impact of sunscreen is unproven and undoubtedly trivial," he said.
However, Pusceddu argued that the coral response to sunscreen exposure was not dose dependent, "The mechanism appears to be on-off: thus once the virus has been switched on by [the chemicals in] sunscreen, toxicity is irrelevant."
Ove Hoegh-Guldberg, director of marine studies at the University of Queensland in Brisbane, said the study is interesting, but notes that many factors are likely to be responsible. "Bleaching is like a runny nose: there are lots of things that could cause it."
Though sunscreens may contribute to coral death, virus-caused bleaching is only a small part of the big picture, he said: "Climate related bleaching is a direct consequence of heat stress and does not involve viruses or bacteria."
Prior to the publication of the study, several marine reserves in Mexico had already banned the use of sunscreen products by reef snorkellers and divers after they observed high mortality of reef organisms in popular swimming areas.