# FAQ

## Question

Q

Would like to know how many drops in one ounce of water equals how many parts per million? Or quart ect.

A

Parts Per Million (PPM)
A unit of concentration often used when measuring levels of pollutants in air, water, body fluids, etc. One ppm is 1 part in 1,000,000. The common unit mg/liter is equal to ppm. Four drops of ink in a 55-gallon barrel of water would produce an "ink concentration" of 1 ppm.

Parts Per Billion (PPB)
One part per billion is 1 part in 1,000,000,000. One drop of ink in one of the largest tanker trucks used to haul gasoline would represent 1 ppb.

The difference between 1 ppm and 1 ppb is important. A prestigious scientific journal recently reported the concentration of a substance as 0.5-1.5 ppm. The real value was 0.5-1.5 ppb. The difference between \$1 and \$1000!

Parts Per Trillion (PPT)

A unit of concentration used to measure vanishingly small levels of pollutants or contaminants in, for example, body fluids. One ppt is 1 part in 1,000,000,000,000. One drop of ink distributed through the water contained in a total of 4 of the 3-million-gallon reservoirs pictured would result in a final concentration of 1 ppt.

The remarkable advances in the sensitivity of modern analytical techniques makes it possible to detect some substances at the ppt level whose presence would not have been detected using earlier assay methods.

Posted on 14 May 2009

Michael Pace
County Director, Agriculture and 4-H/Youth Agent, Box Elder county