From J. A. Robertson, University of Alberta
Edmonton, Canada
Tam Dalyell mentioned the use of urea as a de-icing agent for highways
(Forum, 17 February, p 46). He referred to it as having an “environmental
disadvantage: it oxidises when dissolved in water, giving off ammonia”. The
reaction involved is not oxidation but hydrolysis, and is induced by the
omnipresent enzyme urease.
The ammonia so released can be absorbed by nearby water bodies, and thus
stimulate aquatic life. It is also readily oxidised to nitrate by
chemautotrophic soil bacteria and can also enter water bodies in this form. Urea
itself is very soluble and can serve as a nitrogen source for many organisms
without either the hydrolysis or oxidation reactions.
Incidentally, sodium chloride is not without environmental hazards. In high
concentrations, as can occur along highways, it can harm organisms by lowering
the soil water potential (increasing the osmotic pressure).
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