Treatin' chemical in an unusual way (7)

I believe the answer is:

nitrate

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'chemical in an unusual way' is the definition.
'nitrate' can be an answer for 'chemical' (I've seen this before). I'm not certain of the 'in an unusual way' bit.

'treatin'' is the wordplay.
'treatin' can be anagrammed to 'NITRATE'.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for nitrate that I've seen before include "Fertiliser chemical" , "Tear tin up for fertiliser" , "Nattier (anag.)" , "Natural or synthetic fertiliser" , "Fertilizer" .)

I've seen this clue in The Irish News.

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