Calculating toxicant concentration

[PedroAndrade]

Hi!

In my lab we're preparing a toxicity bioassay using nitrate (NO₃^-) as the test toxicant. The tests we're doing are range-finding tests, to help determine the lethal concentration (LC₅₀) for that species with nitrate.

We are following the lead of another work (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V74-4F02KWG-B&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=172b82c36ff657803f003c89ddaca62d") which used sodium nitrate (NaNO₃) as the source of nitrate. In that article, the test concentrations used for a similar species range from 5 to 160 mg NO₃-N/L. This is where my understanding of chemistry is lacking. I'll try to illustrate my doubts with an example:

If I want to find the LC₅₀ for a solution of 10 mg nitrate/L, what do I calculate exactly?
a) 10 mg of NaNO₃
b) 13,71 mg of NaNO₃ - corresponding to 10 mg of NO₃^-
c) 60,71 mg of NaNO₃ - corresponding to 10 mg of N

My feeling is that b) is correct, but the notation NO₃-N is throwing me off. Can anyone help out with this?

 

[alxm]

I thought it was b) too, lucky thing I asked a friend who's an environmental microbiologist.

It's c). "NO3-N/l" should be read as 'Nitrate nitrogen per liter". So it's just the amount of nitrogen.

 

[PedroAndrade]

Thank you very much alxm! You stopped my day from becoming the new season of 24.