[Coral-List] effect of sunscreen on corals

Douglas Fenner douglasfennertassi at gmail.com
Wed Feb 6 21:01:55 UTC 2019

I was just made aware of a new paper on some sunscreen UV filter
ingredients, though oxybenzone was not tested.

Fel, J-P, et al 2018.  Photochemical response of the scleractinian
coral *Stylophora
pistillata* to some sunscreen ingredients.  Coral Reefs 38: 109-122.


(become a member of the International Coral Reef Society, and ALL the
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One person pointed out to me that when there is strong evidence that there
is an effective chemical that is less toxic, then more toxic chemicals can
be banned.  Says that happens all the time in the insecticide industry.  I
hope there are effective UV filters that are less toxic and useful for

Another points out that the "conservationists" in the dive industry jump
all over easy things like sunscreens, eager to urge people to take action,
but won't touch global warming with a 10 foot pole (my wording).  That's
treating the scratch while the patient dies of a gunshot wound to the
chest, great way to watch the reefs die under our noses, in my opinion.

If there was direct evidence of coral mortality in the ocean caused by a
sunscreen ingredient, the case for banning it would be stronger.  But where
is the evidence of that???  Bleaching has killed billions of colonies all
over the world, massive coral mortality, obvious to anyone.  But where's
the evidence that sunscreens have caused mass mortality?  As someone
pointed out to me, for virtually every chemical, there is a concentration
at which it becomes toxic.  The real question is, are sunscreen chemicals
toxic to corals at the concentrations at which they occur in the ocean
where corals are?  And it has to be in the water able to affect the coral,
if you put a dispersant in, then chemicals that don't readily dissolve in
the water (and surely the manufacturers don't want it to wash off or
dissolve off of people readily) may then have much higher concentrations
dissolved in the water than would dissolve naturally in the ocean, no
surprise if they are toxic, but that wouldn't be the situation where living
corals are in the ocean.  Does oil dissolve in water?  The amount of oil
floating on the surface isn't what kills corals on the bottom, it is the
small fraction that manages to dissolve in the water that affects the coral
on the bottom (unless the coral is so shallow that the oil or tar balls
cover the coral directly).  Even sunscreen floating on the surface, if it
doesn't dissolve in the water, will have little effect on life in the
surface microlayer, I would think.  A small part dissolves, and the
question is, is that enough to damage corals.  The small part of sunscreen
chemicals floating at the surface which dissolves may not stay in the
surface microlayer but diffuse and be carried by water movement into the
bulk water column, and thus might not be nearly as concentrated at the
surface as the non-dissolving portion.  I haven't tested it, I'm not a
chemist, I defer to those with expertise in this area, please enlighten us.

     There is a sentence in the abstract (which is open access at the URL I
posted above) that says: "It first shows that for many organic filters,
measured concentrations were significantly lower than nominal
concentrations, due to the lipophilic nature of the compounds."  Which
sounds to me like they are saying that the concentration dissolved in the
water was less than calculated based on how much they put into the water,
because it doesn't dissolve readily in water.

     Zinc oxide was found to be toxic to the corals.  Also, another
sentence in the abstract says: "The other UV filters tested showed no
adverse effect on coral symbionts or animal tissue up to the concentration
corresponding to their water solubility limit (and even above)."  I
interpret this to mean that you can dissolve all you can of them in the
water and they don't show an adverse effect on photosynthesis (which is
what was measured).  Note that they didn't test oxybenzone, they tested
other UV filters used in some sunscreens.

Cheers,  Doug

On Tue, Feb 5, 2019 at 9:43 PM Bill Allison <allison.billiam at gmail.com>

> I was thinking of sunscreens as one of many insults afflicting the
> microlayer ecosystem, and how important that ecosystem is.
> On Tue, Feb 5, 2019 at 10:38 PM Douglas Fenner <
> douglasfennertassi at gmail.com> wrote:
>> Good point!  Many or most coral eggs float so they would be in the
>> surface microlayer, slicks of coral eggs on the surface on the Great
>> Barrier Reef are large enough you can follow them for a while from
>> airplanes.  I would guess that sunscreens float, but I don't know.  But
>> most areas small enough to be contaminated significantly by sunscreens are
>> not very likely to be self-seeding, especially for the majority of corals
>> that are broadcast spawners.  Still would be an impact on overall coral
>> reproduction, though given that the areas that have large numbers of
>> tourists with sunscreen in the water are minute compared to the world reef
>> area, especially in the Indo-Pacific, which of course is most of the
>> world's reefs, the effect would be pretty small, probably difficult to
>> measure I would guess.  Maybe higher in an area like the Caribbean where
>> tourism is large on many islands.
>> Cheers,  Doug
>> On Tue, Feb 5, 2019 at 2:05 PM Bill Allison <allison.billiam at gmail.com>
>> wrote:
>>> It strikes me that sunscreens will tend to float as will toxins seeping
>>> into the sea from freshwater lenses and fogging pesticides in diesel
>>> carriers, all of which will be harmful to organisms in the surface
>>> microlayer.
>>> Wurl, O. and J. P. Obbard (2004). "A review of pollutants in the
>>> sea-surface microlayer (SML): a unique habitat for marine organisms."
>>> Marine Pollution Bulletin 48(11-12): 1016-1030.
>>> Abstract
>>> Boundary layers between different environmental compartments represent
>>> critical interfaces for biological, chemical and physical processes. The
>>> sea-surface microlayer (uppermost 1-1000 lm layer) forms the boundary layer
>>> interface between the atmosphere and ocean. Environmental processes are
>>> controlled by the SML, and it is known to play a key role in the global
>>> distribution of anthropogenic pollutants. Due to its unique chemical
>>> composition, the upper organic film of the SML represents both a sink and a
>>> source for a range of pollutants including chlorinated hydrocarbons,
>>> organotin compounds, petroleum hydrocarbons, polycyclic aromatic
>>> hydrocarbons (PAH) and heavy metals. These pollutants can be enriched in
>>> the SML by up to 500 times relative to concentrations occurring in the
>>> underlying bulk water column. The SML is also a unique ecosystem, serving
>>> as an important habitat for fish eggs and larvae. Concentration ranges and
>>> enrichment factors of pollutants in the SML in different areas of the
>>> world's oceans have been critically reviewed, together with available
>>> toxicity data for marine biota found within the SML. Overall, the SML is
>>> highly contaminated in many urban and industrialized areas of the world,
>>> resulting in severe ecotoxicological impacts. Such impacts may lead to
>>> drastic effects on the marine food web and to fishery recruitment in
>>> coastal waters. Studies of the toxicity of fish eggs and larvae exposed to
>>> the SML contaminants have shown that the SML in polluted areas leads to
>>> significantly higher rates of mortality and abnormality of fish embryos and
>>> larvae.
Douglas Fenner
Ocean Associates, Inc. Contractor
NOAA Fisheries Service
Pacific Islands Regional Office
PO Box 7390
Pago Pago, American Samoa 96799  USA

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