Trefolex last tin I saw a couple of months ago had a great big message saying how safe it was. Could be I guess but anything that gets heated so it smokes is likely less than safe.

One cutting compound that is nice is called Rocol. Have used it didn't get much burning of it.

Sadly we don't all have CNC machines that can tap an M10 at 3000 RPM in an enclosed environment while flooding the whole deal with coolant.

Hand tapping if Trefolex doesn't give you dermatitus then it won't be hurting you.

Studley