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BRIEF: What nitrate level in drinking water is toxic?


QUESTION:
I would like to know, about nitrite poisoning in sheep. What is the nitrate rate in water that sheep can drink to show signs of toxicity. And what is the normal range of methemoglobin and glutathion in sheep? I didn't find it in the literature. Could you help me?

ANSWER:

Experimentally, nitrate levels of 200ppm are hazardous to sheep, and 1500 ppm will poison them immediately. But 200ppm is far too high for people. And I'd like to see it lower for ewes with lambs. I would argue for much lower levels of nitrate (<10ppm) because very often families share drinking water sources with stock. Children, especially babies, are more susceptible to nitrate than adults (or sheep). In my home county (Tompkins County, New York, USA) they require that there be less than 10ppm nitrate nitrogen in the water which is equal to 44 ppm nitrate. That limit is close to the amount that causes methemoglobin in human babies. (If the water were really that high in nitrate, I hope one would use bottled water to mix up baby formula or be sure to breast feed children), In fact the water is usually below 3ppm.