Salts found in pair of buttocks (9)

I believe the answer is:

arsenates

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'salts found' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'pair of buttocks' is the wordplay.
'pair of' becomes 'arse' (I can't justify this - if you can you should give a lot more credence to this answer).
'buttocks' becomes 'nates' (I've seen this before).
'arse'+'nates'='ARSENATES'

'in' acts as a link.

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