Arsenic is only toxic to our understanding of biology. Some extremophiles have unbelievable resistance to heavy metals, so I wouldn't doubt some configuration of our biology would be resistant to arsenic.
However, with the problems arsenic causes blocking PDH enzyme, causing H2O2 in the cells and a huge list else like IIRC thiamine deficiency.
Then again, life exists in such a broad range of conditions that I find it hard to believe that life couldn't adapt to life with arsenic for one main reason. If it is using arsenic as a DNA base, it means it is sequestering the arsenic rather than leaving it in the cells to do damage.
However, with the problems arsenic causes blocking PDH enzyme, causing H2O2 in the cells and a huge list else like IIRC thiamine deficiency.
Then again, life exists in such a broad range of conditions that I find it hard to believe that life couldn't adapt to life with arsenic for one main reason. If it is using arsenic as a DNA base, it means it is sequestering the arsenic rather than leaving it in the cells to do damage.