is ppb equal to mg/kg?
Parts per million and parts per billion may be converted from one to the other using this relationship: 1 part per million = 1,000 parts per billion. For soil, 1 ppm = 1 mg/kg of contaminant in soil, and 1 ppb = 1 ug/kg. A measurement of 6 mg/kg is the same as 6 ppm or 6,000 ppb, which is equal to 6,000 ug/kg.