Coral vs. Sunscreen Comment Benzophenones: Understanding the Causes, Sources, Prioritizing the Risks and Effects on Global Coral Reef Systems

(Comment for Coral List)




Recently there have been a number of interesting comments regarding coral and sunscreen toxicity on the Coral List and most reflect common viewpoints, but not necessarily including all current scientific views of the sunscreen problem. We (my company) looked into the sunscreen toxicity problem in depth and in detail a couple of years ago as part of some contract research we did for a conscientious non-benzophenone sunblock producer (used a mineral block - titanium dioxide as UV blocking agent) and whom has since decided to withdraw from the sunscreen business entirely, but not because his product showed experimental toxicity in mature hard reef corals. You can read our report and look at our experimental setup, coral condition photos through out the study. It is offered here with the supporter’s permission:


From our work, I can appreciate the need to accurately determine the seriousness of the potential problem, but even more I especially understand how difficult it is to determine the level of threat sunscreen chemicals have on corals and other reef organisms. Our work was private research and only looked at mature corals and was not published, or peer reviewed, though our recommendations for future work recommended studying the toxicity to coral larvae.

The need for sunscreens:

I am not an advocate of sunscreens, don’t personally use them when going in the water and rarely on land, and I don’t recommend them. If the FDA pulled all benzophenone ingredient sunscreens off the shelves tomorrow - it’s ok with me. Primarily because I am convinced that benzophenones are effective in preventing melanoma and as some commenters point out - perhaps may actually increase cancer risks (reduced Vitamin D) - though the benzophenone cancer link is more suspect than fully demonstrated. The American Cancer Society as of March 2015 does not recognize benzophenone as a known carcinogen. 


Earlier studies have been less than conclusive, but found some associations with its role in some skin cancer.


When we say “a known carcinogen” we need to remember that this term alone does not reflect exposure times and or convey the dosages at which a compound may become a carcinogen. The state of California has a long list of chemicals and materials that they consider “known carcinogens” and it does include benzophenone. However, that same lists also includes a wide variety of common medications currently being prescribed by our US medical system. Again for the term to have meaning we have to have context.


The dilemma of ever present carcinogens in our environment is well illustrated at the dated link below. Albeit the understanding of carcinogens has not improved much even among the public or even professionals. If not a totally current scientific article it is at least is entertaining.


I’m not persuaded that the threat created by sunscreens to reef organisms is as great as being portrayed for a lot reasons beyond its potential toxicity. Not because there is zero threat, but that the benzophenone threat priority relative to other threats to coral ecosystems - which are much greater ones - is a comparatively minor threat. Would we be better off eliminating benzophenones use in sunscreens. Probably, but its removal from sunscreens won’t remove it from the marine environment. Here are some points that I would offer to the Coral List:

Natural occurrence of benzophenones:

Most people assume that benzophenones are only man made pollutants and that sunscreens are the primary source in the marine environment. However, benzophenones are widely used as UV inhibitors in a huge variety of industrial and commercial products -  paints, plastics, cosmetics, foods and other products which are used in and around the marine environment. This would include water craft finishes and even the dive gear the coral researcher is using. By volume sunscreens are a minor use of benzophenones.

Perhaps more insidiously and under recognized - benzophenones are produced by a wide variety of ketone producing human food plants such as  grapes, tea plants, papaya and others. Additionally, benzophenones are produced by marine organisms including some brown algae and probably other species. Benzophenones would have been found in the marine environment long before it was synthesized by humans.


Even if we remove benzophenone from sunscreen it will still be in many other products and in human sewage and in the marine environment. If benzophenone is a coral larval toxin in the environment, we are only concerning ourselves with one of the many sources. Should we be look at all sources? 


Previous studies:

Our contract research caused us to make an in depth review of prior research on sunscreen toxicity experiments. I would have to disagree with assessments that Danovaro’s 2008 paper went unnoticed. However, it was largely ignored for good reasons. There were gross experimental design errors, sunscreen application assumption errors, the extrapolated threats were not only mathematically incorrect - the results were vastly under proved/overstated, and they did not reflect dilution/degradation realities. These realities (assuming you first know what they are) are even more difficult to accurately reproduce in representative experimental designs in coral testing due the high levels of uncontrollable and or unaccounted variables in this type of experimentation. Just in the most recent benzophenone studies toxicity seems to be almost exclusive tied to beach bathing, pocket bays with limited exchange - and in the very limited areas where these conditions over lap with reefs.

I have only read the PR release on Dr. Downs et al. recent work. I will be interested particularly in the experimental design and how it represents reality regarding exposure,  dilution and degradation in the environment. I will be surprised if environmental levels of sunscreen ingredients on non-beach sunscreen ingredients - approximate avg. reef sites most of which are not proximate to beaches and if they bear out the studies representations in the UVI and Hawaii on a broad basis.


The security provided by and the need for sunscreens is overstated:

Melanoma is a complex issue and not as directly related to sun exposure as once thought, but is more associated to specific phenotypes, how and when their exposure occurred. It  often stated that melanoma cancers occur most often in exposed body parts. However, under several recent studies this is not supported. Analysis produces no correlation between body area exposed to the sun and melanoma development. To other types of less fatal skin lesions - yes there is an exposure association.

Actual sunscreen usage vs. extrapolated:

Sunscreen isn’t necessary for most people to have safe sun exposure - unless you are a red head and freckled face. Which is a comparatively minor percent of the global population - and becoming smaller. Even then you are more protected by UV resistant “Rash Guard” athletic/water clothing and a hat. Unfortunately, fear marketing strategies by the dermatological medicine practitioners/cancer treatment industry, and related products like sunscreens would make us all believe that sunscreen is vital to prevent melanoma. There are effective products that do not contain benzophenone for the fair skinned and freckled people. These more susceptible people need to be accurately informed of their more environmentally friendly protection options. 

Though I do a lot of diving -  No. I don’t notice the pervasive odor of coconut oil from divers, perhaps in the past. I do notice it at public beaches as. Even though I dive in tropical waters exclusively, and observe not entirely by casual observation that 95% of the divers I see are wearing full rash guards or full wet suits even in tropical waters. This means they have little need of sunscreen. Further, it means to me that what ever threat there is from benzophenone sunscreen chemicals - is primarily coming from sunbathing beach goers and are only threats to public beach proximate reef systems. Reef areas in general are not usually proximate to desirable beach areas - though they do indeed occasionally over lap especially were sunscreen water samples are generally taken. Consequently, dilution factors, absorption, chemical breakdown, physical binding and other sunscreen residue removal rates are difficult to accurately access and will have many variables from reef site to reef site.

Oily surface residues:

Regarding concerns about oily human skin products floating on the surface of the water: First, I should point out that benzophenone-3 weighs 1.20 g/cm3 and seawater weighs 1.025 g/cm3. Benzophenone is not soluble in water, but rather volatile organic solvents such as ether, acetone and is lipophilic. This brings into question a lot of the assumptions about where benzophenones end up in the water column and benthos and when. If its suspended in the oils it may be at the surface with them. If it separates completely, it’s briefly in the water column depending on particle size, water agitation and then likely to be tied up in bottom sediments. Since coral larvae come near the surface at night there are few places where wind currents would not have pushed day time surfaces residues of reef areas by night. Night divers are not likely wearing sunscreen.

While risks of benzophenones and related chemical avobenzone, octisalate, octocrylene, homosalate and octinoxate are a concern, those same chemicals and the oils they are in - whether truly dissolved or suspended in sun screen oils - join a host of other surface oils on the ocean. This oil residue includes petroleum lubricants and fuel films, algae decomposition oils, and fish and other marine animal oils. What remains of these oils depending on local site variables and activities affect each other and their interactions with the marine life forms. Additionally we know little about biological uptake by other plankton and how fast this occurs to reduce these residues. Additionally, much of the past experimental work does not mesh well with wind loading that carries oily residues onto beaches thereby stripping them continually from the environment - and previously extrapolated levels in the marine environment.

Prioritization of coral threats:

I think there is a lot about benzophenone sources and toxicity potential that we don’t know, and I can’t agree with some commenters that any current studies offer a “block buster” revelation regarding coral benzophenones relationship with coral bleaching. Rather they raise more questions - not the least of which is what do we blame coral bleaching on hundreds and or thousands of miles from any human access, activity and habitation. 

I do think that the human skin product impacts on corals and coral larvae - on a contact probability and ocean volumetric basis - are pretty far down the coral threat priority list compared to sewage (which is another source of benzophenones), other excess nutrients, industrial and agricultural pollutants, elevated CO2, biological response to elevated CO2 and excess nutrients and all the other human species impact extension chemicals going into the environments.

My point here is that comparatively minor and or site specific environmental threats such as sunscreen benzophenones, should be a lower priority for our research resources as symptoms - than the undeniable cause of those symptoms - human over-population impacts. Most of us just don’t get the dramatically greater extended impacts that human species have on the environment compared to other species per unit body mass. I’m not saying ignore relatively minor threats like benzophenones, but the press it gets far exceeds the proportionality of its threat and dangers. Again, coral bleaching occurs in many areas around the world that have no human benzophenone sources present.

My opinion is that the greater threat to corals and the human species is our continued denying that human overpopulation is the primary cause of the degree of negative anthropogenic environmental impacts. It is not logical or a wise problem solving resource utilization to worry about the parts per trillion of possibly toxic human skin products introduce in our environment, if you aren’t also working at a much higher priority on workable plans to reduce the major causative agent of over population of humans and their general negative affects and displacement of other species in the global marine environment simultaneously.

Best regards,

Durwood M. Dugger, Pres.

BCI, Inc.