The closest exposure to arsenic he might have at work is with the arsenic compounds use to preserve tissues. Most arsenic found in the US commercially is combined with a copper solution as wood preservative.
Rat poison no longer contains arsenic, instead using an anti-blood coagulant.
The EPA has long had a very strict standard for arsenic in drinking water. So truthfully where anyone would get enough (likely arsenic trioxide) to poison would be quite rare.
Liberals. Conservatives? That's a different EPA standard.