Re: What strong acids and bases are produced by life as we know it?

Dear questioner,

This is a great question. First, let's be clear about use of the word "strong" when applied to acids and bases. Many people use the word "strong" to mean "corrosive". However, chemically a "strong acid" means one with a high tendency to dissociate and liberate protons in solution. Of course, strong acids (chemically) often are strong (corrosively) and the examples that you mention, hydrochloric and sulfuric, would be strong in both senses.

To your question. Yes, hydrochloric acid is secreted in the stomach. The low pH is required for enzymic activity, principally that of a protease called pepsin. I believe that you're also correct about the ability of the Tiger Cowrie to squirt sulfuric acid - there are numerous references to this on web pages, although I found it hard to pin down a definitive source.

Another group of organisms that secrete sulfuric acid are the nudibranchs (it means "naked gills"), or sea slugs. These are fascinating and colourful marine molluscs that you'll often see on rocks if you go scuba diving. There is a discussion on acid secretion in these organisms at the Sea Slug Forum, which also provides references about acid glands in nudibranchs.

These are all the examples of strong acid secretion that I could locate. Strong bases was even more difficult! Many fluids secreted by organisms are mildly alkaline (pancreatic and seminal secretions would be examples), but it seems that we don't see extremes of alkaline pH like we do for acid pH. One example that I did find is in the hindgut of certain insects, particularly beetles (Coleoptera) and caterpillars (Lepidoptera). A paper in the journal Applied and Environmental Microbiology describes a beetle in which the hindgut pH is > 10. Other references describe a hindgut pH as high as 11, required for the activity of digestive enzymes.

So there are not many examples of either very strong acids or bases in biology. Your question might be better addressed to a zoologist - there are so many organisms, both known and waiting to be described, that I wouldn't be in the least surprised to find more examples of both strong acid and strong base secretion in biology.