Toxicity of carbide waste to heterotrophic microorganisms in caves.

The spent carbide from acetylene-generating lamps used by spelunkers has long been assumed to be toxic. Pure cultures ofE. coli, S. cerevisiae, andB. subtilis were inhibited within 15 minutes by addition of a 1% solution of waste carbide. The heterotrophic microorganisms which form the food base in caves were depressed 81% in 1 hour by the application of fresh carbide waste to a cave stream mudbank. The effects were temporary as the toxicity was lost when the extremely alkaline pH of the waste was neutralized. The reduction in pH occurs naturally over time by atmospheric and substrate buffering and is probably related to soil type and available moisture.