Cacodylic acid is widely used as a buffer in conjunction with fixative systems for the preservation of cellular structure. Although this material is quite toxic and contains arsenic compounds, in some instances it is preferred to phosphate buffers, which can give rise to precipitation with uranyl acetate when used as an "en block" stain. Phosphate buffers also can form artifactual granules when used with glutaraldehyde and osmium tetroxide. But, since arsenic is a potent carcinogen, many laboratories try to get out of the habit of using arsenic buffer when other buffers might work just as well. Those who use cacodylic acid routinely (e. g. it is in permanent laboratory use), report that it is easy for dust to accumulate on the outside of bottles, the inside of laboratory glassware in line to be washed, etc. And since the exposure to arsenic compounds is cumulative, one has to be doubly careful to avoid exposure.
The point here is to not scare everyone out of using cacodylic acid, but only to point out that because of these hazards, when less hazardous alternatives are available, those alternatives should be considered.
* Available while supplies last
