Dr Karl Kruszel­nicki

Australian Geographic - - Contents - with Dr Karl Kruszel­nicki

Co­ral-killing chem­i­cals

ON A TRIP to the Gala­pa­gos Is­lands, our guide asked us not to use sun­screen at one reef. He told us it was very frag­ile, and quite small, and that the lo­cal cur­rents tended to trap con­tam­i­nants. Un­for­tu­nately, it seems one pop­u­lar sun­screen chem­i­cal at­tacks baby co­ral.

I re­searched this later and found the chem­i­cal is oxy­ben­zone – one of the most widely used or­ganic UVA fil­ters.

It’s also called BP-3, or Ben­zophe­none-3. Be­sides UVA, it also ab­sorbs UVB, so it blocks UV light rang­ing from 270 to 350nm. (Not many or­ganic sun­screens block both UVA and UVB.) Oxy­ben­zone is used in hair­sprays, cos­met­ics, nail pol­ishes – and in more than 3500 sun­screens world­wide.

Oxy­ben­zone, I dis­cov­ered, has four sep­a­rate bad ef­fects on baby co­ral.

First, it pre­dis­poses co­ral to bleach at lower tem­per­a­tures. If the ocean is hot­ter than nor­mal, then there’s even more bleach­ing. Sec­ond, oxy­ben­zone dam­ages the DNA of co­ral. The over­all re­sult is that corals with dam­aged DNA are less able to re­pro­duce, or their off­spring are likely to be sick. This leads to each gen­er­a­tion of co­ral be­ing less healthy than the one be­fore.

Third, it acts as a pow­er­ful hor­mone dis­rup­tor. It forces ju­ve­nile co­ral to pro­duce too much cal­cium car­bon­ate, so they to­tally en­case them­selves in their own skele­tons, which kills them. Fi­nally, oxy­ben­zone de­forms ju­ve­nile corals; they stop swim­ming, change shape and their mouths grow unusu­ally large.

Oxy­ben­zone can be toxic to baby co­ral at lev­els equiv­a­lent to one drop in six and a half Olympic swim­ming pools. Reefs in Hawaii and the USA’s Vir­gin Is­lands have been mea­sured at lev­els as high as 1.4 mil­lion parts per tril­lion.

We know that ti­ta­nium ox­ide and zinc ox­ide are not as harm­ful to co­ral as oxy­ben­zone. So when swim­ming near reefs you could try to use sun­screens with th­ese or other less harm­ful chem­i­cals in­stead, or you could cover up.

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