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
|The litmus test|
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.