Thursday, February 24, 2011

Acidification and Disintegration, Part II

Yesterday, I set up the issue: the ocean is increasingly acidic, thanks to ever more CO2 in the atmosphere. It's already affecting creatures as far away as Antarctica, and is decimating the wild oyster in the northwest U.S.

Learning this, and how natural carbonic acid in rain dissolves beached shells, I decided to do an experiment of my own. Just what does an acid really do to a shell, and how long does it take? Plus, with all the plastic waste swirling in the ocean, how might ocean acidification affect plastics?

So off to work I went. First, the ingredients:
Distilled white vinegar, 2 Atlantic surf clams, 1 blue mussel,
1 #4 plastic, 1 #5 plastic, 1 #6 plastic, and unk plastic bucket
As mentioned before, the pH scale measures acidity/alkalinity, 0 being most acid, 14 being most alkaline, 7 being neutral. Pure water should have a pH of 7. By mixing with CO2 in the air, rainwater tends to have a pH of about 5.6. What's the pH of distilled white vinegar? Anywhere from 2.0 - 3.4. The best way to tell? Test it yourself:
The litmus test
Seems suppliers might be a little bit cheap with the vinegar these days - the paper looks more like 4.0 than 3.4. Still, 3.4 is very mild -- about as acidic as an apple. (Lemon juice is 2.3, a can of Coke is 2.5.) Certainly nothing dangerous to a person. But what about a shellfish? Let's see. Here's the moment I first put all the ingredients into the bucket:
Instant reaction
Like Alka-Seltzer in a glass of water, the shells immediately started reacting with the vinegar.

A quick word about seashells. As, say, a clam is growing, it develops a thin "skin" around its outside, called the periostracum. It's like a tiny membrane that wards off the outside world - including weak acids. But it's delicate, fragile, and usually worn away as the creatures lurch back and forth in tides, or burrow into the gritty sand on the seabed. In most cases, periostracum will not help a mature bivalve fend off an acid attack.

Back to the experiment. I poured enough vinegar into the bucket to cover the shells. Twice a day, I fished out the larger of the two surf clam shells and photographed it. Each morning I topped off the vinegar, and I replaced the vinegar twice through the length of the experiment. The pH of the solution ranged anywhere from ~3.4/4.0 to about 6.0 depending on how fresh the vinegar was. Here's what happened:
Start of experiment --
shell intact, periostracum worn in places
After 1 day -
periostracum darkened, bubbling
After 2 days
After 3 days
After 4 days
After 5 days
After 6 days
After 6 1/2 days
After 7 days
After 7 1/2 days
That's it. Gone. After just over a week, the Atlantic surf clam that had been half a foot long... is gone. In fact, all 3 of the shells I put in were gone. Leaving nothing behind but shreds of their empty skin. What do you think happened to all the various plastics? Long-time followers of the Flotsam Diaries will hardly be surprised by the answer:

Of course the oceans aren't predicted to drop to a pH of 3.4. Or even 6.0. They don't have to. The tiniest drop, from 8.1 to 7.8, causes a cascade of crises - some shellfish devote so much time to building & repairing their shells that they don't have the energy to devote to muscles, movement, immune systems, or procreation. A drop of just .2 killed half the copepods in a test group in a week. One chilling experiment showed that a drop of .4 killed 99.9% of a species of brittlestar larvae in 8 days.*

This isn't a small problem, or a made-up issue. This is reality, happening now. These are foods not only eaten by people, but are also the base foods for many of the other major foods we eat.

But who knows. Creatures have adapted before -- though it took them millennia, not decades. Perhaps they'll be able to get their energy from the plastics swirling in the water. Because, as we all know, plastic is forever.
Day 7 1/2 - The end

* See this Scientific American article of August 2010 for these and many other examples.


  1. This is so fascinating! And frightening!

  2. It was eye-opening for me when I was researching. Watching the shells -- the life -- dissolve away while the little bottle caps just floated on happily. Yuck.