I believe it is fair to say that arsenic and selenium are natural antagonists.
At any rate, as a rule, substances should be studied as push-pull pairs in the body. Rarely if ever in isolation – that is usually a mistake, even if I am wrong about selenium and arsenic as being one of those push-pull pairs. Other push-pull pairs may include sodium-potassium, calcium-magnesium, and zinc-copper. Really, in the body, nearly every substance needs to be balanced directly with respect to at least one other substance, and indirectly with everything else.
Could an unintended consequence of selenium intoxication be arsenic deficiency (and possible taurine and/or polyamine deficiency)?
Could an unintended consequence of arsenic intoxication be selenium deficiency?
Can at least part of the increased cancer incidence from arsenic intoxication be due to selenium deficiency? Warburg considered the carcinogenicity of arsenic to be evidence for respiratory impairment, and it probably is, but if I recall, he did not also consider a possible effect of selenium deficiency (subsequent to arsenic intoxication) on higher rates of cancer.