is mg/kg ppm or ppb?
A measurement of 6 mg/kg is the same as 6 ppm or 6,000 ppb, which is equal to 6,000 ug/kg. Concentrations of chemicals in water are typically mea- sured in units of the mass of chemical (milligrams, mg or micrograms, ug) per volume of water (liter, L, l).