pH gradient

Definition

The downward drift of pH from near-neutral bulk water to acidic conditions at the metal interface beneath a biofilm.

As metabolic acids accumulate inside the film, pH drifts downward at the metal surface even while the bulk water stays neutral. The local acidity destabilizes protective films and increases the anodic reaction rate. Acid-producing bacteria amplify this effect, making re-passivation of the metal unlikely.

Related concepts

Acid-producing bacteria (APB) · Passivation · Mature community

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Part of The Blueprint of Water · 🧪 chemistry