Iron-rich rock helps oceans sink atmospheric carbon

First published in Chemistry World, 05.04.18

Adding crushed rocks containing magnesium and iron minerals to seawater allows it to sequester more carbon from the atmosphere, geoscientists have shown.

Oceans are the world’s most efficient carbon store. Around a quarter of all anthropogenic carbon dioxide emissions are sequestered into the sea, and oceans could take in up to 80% of manmade carbon if the process, which usually takes centuries, could be sped up.

A team led by Eric Oelkers from University College London, UK, spread finely milled peridotite – an ultramafic rock that is rich in iron – in tanks of seawater with simulated wave activity. As the powdered rock dissolved it raised the pH of the water, enabling it to react with more atmospheric CO2. The sequestered carbon mineralised into aragonite, a form of calcium carbonate, which sank to the bottom of the tanks.

If powdered peridotite was added to actual oceans, the researchers say, the aragonite would sink to the ocean floor and become sediment, storing carbon permanently. And in nature, aragonite is important for the calcification of corals, so it may even have the added bonus of supporting coral growth.

So far, the approach has only been tried in laboratory simulations. Oelkers says the method needs further scrutiny before it could be seen as a viable way to reduce atmospheric CO2.

‘With upscaling, there are many, many things to consider, some of them unexpected,’ he tells Chemistry World. For example, the extra iron in peridotite rocks could cause plankton blooms. The rocks also contain materials that are harmful to marine life, such as nickel, and it is not clear what impacts these would have on a large scale.

The energy and money required to mine and mill the peridotite also needs to be considered. The researchers propose that the method should be limited to coastal areas where peridotite is common, in order to limit carbon emissions from transport.

Juerg Matter, a geoengineer at the University of Southampton who was not involved in the research, says further refinement of the method could help lower the energy costs of peridotite powder production and save on emissions.

‘The question is really what the acceptable grain size could be,’ he says. ‘Is it really necessary to produce ultrafine particles, or could we tune the process [so] less milling time is required?’

Hawaii seeks to ban ‘reef-unfriendly’ sunscreen

A proposed Hawaiian bill aims to stop the sale of lotions containing certain UV-filters, but their effects on coral are disputed.

Nature, 03.02.2017

Legislators in Hawaii are trying to ban the sale of sunscreens that contain two UV-filtering chemicals, after studies suggested that they harm coral reefs.

On 20 January, Hawaii state senator Will Espero introduced a bill which would ban sunscreens containing oxybenzone and octinoxate in Hawaii (except under medical prescription) to the state Congress. Espero argues that a ban is important to preserve the state’s tourism industry, because Hawaii relies heavily on tourists attracted by its coral reefs.

The bill is already attracting attention from other regions with economies reliant on reefs, including Palau and the British Virgin Islands, Espero says. But manufacturers argue that more evidence is needed to warrant a ban.

A bar in the state of Hawaii would be the strongest political measure yet taken against the chemicals – although some manufacturers already sell “reef-friendly” sunscreens without them, produced in response to scientific and consumer concerns. “Since there are eco-friendly sunscreens on the market now, a total ban hurts no one,” Espero argues.

In November 2015, a group of European Parliament members proposed a motion to ban oxybenzone in cosmetic products throughout the European Union, but that legislation has stalled.

Sunscreen research

Espero’s bill draws largely upon research done by US scientists led by Craig Downs, executive director of the Haereticus Environmental Laboratory in Clifford, Virginia. In 2016, his team reported that oxybenzone and octinoxate could stunt the growth of baby corals, and that oxybenzone was toxic to seven coral species in lab tests1.

A 2008 study from a different group had found that oxybenzone is likely to cause coral bleaching both in the lab and in the wild in several tropical regions2. Other studies have suggested that oxybenzone also acts as an endocrine disruptor among marine creatures such as shrimps and clams3.

In ongoing follow-up work – which has not yet been published – Downs’ team detected oxybenzone contamination of up to 4,000 parts per trillion (ppt) in the waters off the most popular beaches of the Hawaiian island of Maui. An oxybenzone concentration of around 400 ppt over several days is enough to induce coral bleaching in warm waters, they say. The team suggests that when people snorkel or swim, sunscreen washes off their skin and out into the reefs.

“In many geographic locations, oxybenzone and sunscreen pollution poses a serious environmental hazard,” says Downs.

But other reef scientists are more circumspect about the role of sun-screen chemicals in coral-reef destruction. Many factors damage coral reefs, says Jörg Wiedenmann, head of the Coral Reef Laboratory at the University of Southampton, UK, but he agrees that sunscreen pollution might be detrimental in areas with lots of tourists.

“Banning sunscreen will not solve other problems: for example, temperature anomalies, overfishing, coral predators and the big issue of coastal runoffs that pollute and destroy reefs,” he says. “But if you have places with a high load of tourists going in, it is not unreasonable to stay cautious and say, ‘Yes, there may be additive effects.”

Disputed effects

But sunscreen manufacturers such as L’Oréal disagree that a ban is needed. “Regulatory decisions have to be made on sound scientific evidence and multiple studies,” says Marc Leonard, head of L’Oréal’s Research & Innovation, Environmental Research department in Aulnay-sous-Bois, France. “They have to be completed by different teams to provide a significant bundle of evidence. We are very far from it in this case.” Despite this, says Leonard, L’Oréal are working on making sunscreen products without oxybenzone, in anticipation of a possible ban.

L’Oréal has not itself reported any tests on the effects of oxybenzone or octinoxate on coral reefs. In June 2016, the manufacturer presented work done with researchers at the Scientific Centre of Monaco, on a different UV filter chemical in its sunscreen, called avobenzone. The scientists reported an adverse effect on corals at the high concentrations of 5 milligrams per litre (5 parts per million) – but that has little relevance to normal levels of exposure.

The Consumer Healthcare Products Association, a national trade association for manufacturers based in Washington DC, says that it will oppose a ban until there is more evidence. “We sympathize with the desire to preserve Hawaii’s coral reef, but there is no scientific evidence that under naturally occurring conditions, sunscreen ingredients are contributing to coral-reef declines,” says a spokeswoman for the group.

Downs says that his team has seen a clear effect in Maui – and that he feels there is already enough evidence to justify a ban there. Some Hawaiian politicians have tried to push for more funding to support research into the issue. But a bill to the US Congress, asking for funds for the University of Hawaii to further investigate the effect of sunscreens on reefs, stalled in February last year.

“We have advocates and science on our side,” Espero says. “Fishermen, boat owners, sailors, ocean-sports enthusiasts, ocean-tour operators and environmentalists rely on the ocean for recreation and jobs. Opponents will be out there, but supporters as well.”

Nature
doi:10.1038/nature.2017.21332
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