probably microplastics getting picked up with coffee grinders when edges of bud/leaf/stem contact the lid at high velocity
also pay attention to what kind of plastic/materials are in the device no matter what type of grinder you choose, as to compatibility with isopropyl, some of the metal twist grinders for example will have a dry sift screen section and sometimes that screen will be attached with some sort of glue, whereas some seem to be just pressed into that section of the grinder, being able to iso out that screen is crucial
also pay attention to what kind of plastic/materials are in the device no matter what type of grinder you choose, as to compatibility with isopropyl, some of the metal twist grinders for example will have a dry sift screen section and sometimes that screen will be attached with some sort of glue, whereas some seem to be just pressed into that section of the grinder, being able to iso out that screen is crucial