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I pay attention to my ecological footprint.  I can’t say that I’ve tried them all, but I have completed most of the footprint calculators I can find.   I can’t recall one that did not calculate my greenhouse gas impact, labeling it my greenhouse gas footprint.  Many report the amount of energy I use, turning it into an energy or fossil fuel footprint.  Some point out my water use, calling it my water footprint.   Footprint is a metaphor for the mark I make on the planet, my impact.  My energy use is tough on the planet.  I take depleting hydrocarbon resources and I convert them to energy, CO2 and water.  I use the energy, wasting a lot of it, and release the CO2 and water.  I destroy hydrocarbon resources, resources that don’t replenish on a time scale close to my use.  I make CO2, releasing it to the atmosphere where it will not be removed on a time scale close to my use.  I use more water than I make, but I actually don’t destroy water.  The hydrological cycle returns every drop of water I use back for re-use on a time scale close to my use.  I don’t destroy the elements or even the molecule of water, I just borrow it from the ecosystem, only to return it at a later time where it is pretty quickly returned to me.   I have a wood footprint.  Trees are cut down somewhere everyday so that I can use paper. Society makes a lot of paper and my footprint for trees is larger than what goes into the paper I touch. I have to take some credit for society’s use of paper, hoping that attempts that I make to conserve and recycle paper dominate my footprint.  I haven’t bought any concrete recently, but I drive on roads made from concrete, roads that are constantly been repaired.  Limestone is  fossilized shells that are a depleting resource that does not replenish on a time scale commensurate with society’s use.  I own part of society’s limestone or concrete footprint even though I am not personally mixing the concrete.  I own some part of the CO2 emissions, adding to my greenhouse gas footprint.  None of the footprint calculators I’ve found report my limestone footprint.   For most people, it would be the society’s use divided by the population.  Some footprints you control, others are determined by society.  Some are a mix of the two. 

 

I hadn’t thought about my platinum footprint until about a month ago.  New contact lenses brought new advice:  ditch the multipurpose solution and use a peroxide cleaner.  A new case comes with each bottle of peroxide cleaner with instructions to throw away the old case including the platinum neutralizing disk.  Could a throw away disk really be platinum?  Platinum group metals are, after all, a finite and depleting resource, on many lists of critical metals, and a resource that is already widely recycled.  It turns out that my new contact cleaner comes with a disposable platinum catalyst. 

 

My platinum footprint is a mixed footprint.  I buy some platinum containing things, but most of my platinum use is baked into society. Using national consumption, my platinum footprint is about 90 mg of platinum per year.[1]  I believe my personal platinum footprint is only about a third of the per capita national consumption. I don’t buy platinum metal for investment or jewelry.   The largest use is in cars, but that is recycled very effectively and my car is 7 years old. My personal use is more on the order of 37 mg per year[2].

 

Changing my contact lens cleaner increases my platinum footprint by over 15%.  Peroxide cleaning solutions have performance advantages. They are very effective at killing pathogens that cause severe eye issues. Peroxide supposedly stings like crazy in your eye, and must be “neutralized”.  Hydrogen peroxide is neutralized by catalytically decomposing it to water and oxygen, creating visible bubbles.  Enzyme tablets were once used[3], now replaced with a platinum catalyst disk in all products I found on store shelves.  Deactivation of the neutralizing disk, though I’ve yet to observe it, requires that it be replaced monthly.

 

The platinum on each disk is around 600 micrograms[4], covering a plastic support weighing about 0.8 grams[5].  The platinum on the disk is worth less than 2 cents at current prices, or about 20 cents for a year’s worth.  There are a lot of contact wearers, almost 41 million in the United States[6]. 93% now wear soft contacts9 and recent data indicates 20% use peroxide cleaners[7], a number that is growing.  Contact users trash 1,700 troy ounces of platinum per year. They trash over  $1.5 million per year. 

 

I am amazed that platinum is being trashed when it appears recycling it would be relatively easy.  I am also confused that platinum is being used in this application at all.  Homogeneous enzymes were replaced with heterogeneous platinum in contact care, presumably to eliminate the possibility that forgetful users would fail to introduce the enzyme.  The platinum disk attached to the contact case is pretty fool-proof.  There is a rich literature on immobilizing enzymes, including peroxidases derived from a number of plant and fungal sources.  If there is a reason immobilized enzymes wouldn’t work for neutralization, I can’t find it.  It could be that the chemistry to immobilize the enzymes actually makes them more expensive than platinum.  Many metals decompose peroxide.  The less expensive platinum group metals do.  So do supported catalysts of iron and copper oxide.  If there is a reason cheaper metals wouldn’t work for neutralization, I can’t find it either.  I am left scratching my head in disbelief that platinum is used in such a disposable application, one that now dominates my platinum footprint. Finding another solution or finding a way to recycle would make a big difference. 

 

I wish a 15% decrease in my carbon footprint was so easy.

 

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Mark Jones is Executive External Strategy and Communications Fellow at Dow Chemical since September 2011. He spent most of his career developing catalytic processes after joining Dow in 1990. He received his Ph.D. in Physical Chemistry at the University of Colorado-Boulder doing research unlikely to lead to an industrial career and totally unrelated to his current responsibilities.

 


[1]  using 29,800 kg  of Pt demand for North America from the Johnson Matthey PGM Market Report for November 2015 and 318.9 million people in the U.S. from the 2014 World Bank statistics

[2] Using  Pt demand for North America from the Johnson Matthey PGM Market Report for November 2015 and subtracting automotive, investment and jewelry

[3] Christie, Caroline L., and John G. Meylerr. "Contemporary contact lens care products." Contact Lens and Anterior Eye 20 (1997): S11-S17.

[4] Kasey Jon Minick, Manal M. Gabriel, Leroy Wainaina Muya, Walter Lee Nash, George Edward Minno (Novartis); WO 2011062959 A1, "A hydrogen peroxide solution and kit for disinfecting contact lenses", published 26 May 2011 (filed 17 November 2010).

[5] average weight of disks from Alcon Clear Care, Equate and Bausch+Lomb PeroxiClear.

[6] Cope, Jennifer R., Sarah A. Collier, Maya M. Rao, Robin Chalmers, G. Lynn Mitchell, Kathryn Richdale, Heidi Wagner et al. "Contact lens wearer demographics and risk behaviors for contact lens-related eye infections—United States, 2014." Morbidity and Mortality Weekly Report (MMWR) 64(32), 21 August 2015, pages 865-870.

[7] Chalmers, Robin; "A Fresh Look at One-Step Hydrogen Peroxide Lens Disinfection", Review of Opt. Published August 2014. (Supplement, reprint CCS14015AEi).