Question

3. Look at the results for arsenic.
   1. What is the highest levels allowed (MCL) for arsenic?
   2. What is the MCLB for arsenic?
   3. What was the average level detected?
   4. The units of measurement are ppb. What does ppb mean?

Answer 1

I am assuming that you are talking about arsenic levels in water.

a) Highest levels allowed for arsemic- 10 ppb (parts per billion) in drinking water as set by U.S. Environmental Protection Agency (EPA)

The World Health Organization recommenda arsenic limit of 10 -gm/L

b) MCLB for arsenic as revised by U.S. EPA is 0.01 mg/L. MCLB is the highest level of contaminant allowed in drinking water (Maximum containment level) for biosafety however the MCLG (maximum containment level goal is 0.0 mg/mL).

c) The average level detected- drinking water in U.S. on an average contains 2 µg/L of arsenic (EPA-1928c).

d) pbb stands for parts per billion. It is the  number of units of mass of a contaminant per 1000 million units of total mass. (1 µg/kg)

in case of water, 1 ppb is equal to 1 µg/L.

Hope this helps.

:)