**Microgram **(μg, μgs)
The prefix "micro" means 1/1,000,000 = 1e-6. Therefore, 1 microgram =
0.001 milligram = 0.000001 grams, or 1,000,000 μg = 1 g. 1 μg = 1e-9 kg.

**1,000,000,000** (**One billion**)

**Parts per billion **

Represents the concentration of something in water or soil. One ppb represents one microgram of something per liter of water (ug/l), or one microgram of something per kilogram of soil (ug/kg).

ppb means **mcg**/L.

mcg/ug

2 µg of Hg per mL, which is the same as 2,000 µg per liter; or 2,000 ppb or parts per billion .