system
Given the following post, respond as if you're commenting on Reddit:
human
Why is dimethylMercury highly toxic, while ethylMercury is safe?

I recently saw a video by “Chubbyemu”, in which he shows the symptoms of a scientist who comes into contact with dimethylMercury. How does this cause so much neurological damage, while ethylMercury is safe to use, such as in vaccines? 

Edit: And what is the chemical reason for this? What makes dimethylMercury lipophilic, causing it to stay in fatty tissue for large amounts of time, while ethylMercury clears from the body much faster ?
gpt
The biological half life for ethylmercury is estimated to be 7-10 days (Clifton, 2007). Dimethylmercury is metabolized into methylmercury, which has a half life of ~50 days. So, dimethylmercury effectively exposes the body to the hazard for a lot longer. 

Methylmercury stays in the body because it complexes with cysteine containing peptides. This methylmercury-cysteinel complex is recognized by the body as methionine, an essential amino acid. This lets it get distributed throughout the body.

The biological impacts of ethylmercury haven't been studied as well, though ethyl- also spreads throughout the body. Since the biological half life is about 5x shorter, it most likely gets picked up via a waste pathway and destroyed.