Balloon
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It's a tenuous relationship, nutrients like nitrates, urea, phosphate are reckoned to be water pollutants, and a friend has just been fined in the mid five figures £ for "polluting" a nutrient poor moorland by giving one lot of supplementary feed to sheep, in an old quarry...
It's a tenuous one, and I suspect it often has more to do with extorting fines than with any actual damage.