Understanding Nitrate Concentrations: Are These Rural Wells Safe for Drinking?

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Discussion Overview

The discussion revolves around the safety of nitrate concentrations in rural well water for drinking purposes, specifically addressing the implications of different units of measurement (NO3-/L vs. NO3- N/L) and the necessary conversions to assess whether the reported concentrations exceed the health guideline of 44.3 mg NO3-/L.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants express confusion regarding the unit NO3- N/L and its implications compared to NO3-/L, questioning the significance of the nitrogen designation.
  • One participant suggests that the nitrogen cycle's complexity necessitates distinguishing between different forms of nitrogen in water.
  • Another participant asserts that for every mole of NO3-, there is one mole of nitrogen, implying a straightforward comparison of values against the limit without conversions.
  • Contrarily, some participants argue that ppm typically requires weight/weight conversions, indicating that the reported values may not directly correspond to the guideline without further calculation.
  • One participant attempts a conversion calculation to clarify the relationship between the two units, seeking confirmation of their understanding.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the reported nitrate concentrations can be directly compared to the guideline without conversions. There are competing views on the necessity and method of conversion between the different units.

Contextual Notes

Participants highlight the potential complexity of conversions due to the differences in molecular weights of nitrogen and nitrate, as well as the implications of measuring concentrations in different units.

Who May Find This Useful

This discussion may be of interest to individuals studying environmental science, water quality, or those involved in public health assessments related to drinking water safety.

sdoug041
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The question:

Nitrate concentrations exceeding 44.3 mg NO3-/L are a concern in drinking water due to the infant disease, methemoglobinemia.

Nitrate concentrations near three rural wells were reported as 0.01 mg NO3- N/L, 1.3 mg NO3- N/L, and 20.0mg NO3- N/L. Do any of these three wells exceed the 44.3 ppm level?

The problem:

I have no problem with conversions, it's just the units in this case. I've asked peers about the NO3- N/L unit and they said the N stands for nitrogen. If this is so, I don't know what the implications are. Whats the difference between the NO3-/L and NO3- N/L unit?
 
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sdoug041 said:
0.01 mg NO3- N/L

Doesn't make sense to me.

I can easily imagine NO3- reported as 0.01 mg N/L, but the way you have it written it is - to say the least - strange.
 
sdoug041 said:
I have no problem with conversions, it's just the units in this case. I've asked peers about the NO3- N/L unit and they said the N stands for nitrogen. If this is so, I don't know what the implications are. Whats the difference between the NO3-/L and NO3- N/L unit?

Hmm, I've https://www.physicsforums.com/showpost.php?p=2162757&postcount=2"..

But to elaborate a bit more; you have the whole nitrogen cycle, so nitrogen in water (with living stuff in it) is being converted between nitrate, nitrite, ammonia, etc.
Therefore they distinguish between "N/L" nitrogen per liter (the mass of N from all compounds) "NO3- N/L", nitrate nitrogen per liter (just the nitrate nitrogen) and nitrate/L (the mass of nitrate, including oxygen).
 
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But for every mole of NO3-, there is 1 mole of N... So is there no conversions to be made here? I can just simply look at the values and if they are less than 44.3, they don't exceed the limit?
 
sdoug041 said:
So is there no conversions to be made here?

ppm is usually weight/weight, so you need some conversion.
 
But a mg/L is a ppm, at least concerning aqueous solutions.

there is 10^6 mg of water in a litre.

I think I'm still missing something though. It can't be as easy as just looking at the given values...
 
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sdoug041 said:
But for every mole of NO3-, there is 1 mole of N... So is there no conversions to be made here?

Your units are in mg/L, not mol/L. One mole of N doesn't weigh the same as 1 mole of NO3-
 
Ah that is a good point, it's starting to become a little clearer.

So:

(0.01 mg NO3- N/L) x (1 mol N / 14000 mg N) x (1 mol NO3- / 1 mol N) x (62000 mg NO3- / 1 mol NO3-)

= 0.04 mg NO3-/L

Am I understanding this concept correctly?
 

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