Replied by Ted (Bangkok, Thailand)
If the detergent has only borax, since the amount taken is low, most people would use that.
Food grade or pharmaceutical grades, 500 grams are available from scientific sellers, and chemical supplier, or a chemists, but most people find the difficult to obtain them. For me, I get them from a chemical supplier.
In practice taken in small amounts such as a small pinch are generally do not have problems. Most contaminants I found actually don't come from those, but from common things we consume everyday are more toxic such as tap water which have more contaminants.