Final answer:
The term ppm stands for parts per million, a measurement unit for solute concentration in a solution. For instance, 1 ppm of fluoride ion is the maximum safe level in tap water according to the EPA. Conversion from ppb to ppm is done by recognizing that 1 ppm equals 1000 ppb.
Step-by-step explanation:
The term ppm, which stands for parts per million, is a unit of measurement used to express the concentration of a solute in a solution. When we say the concentration of a substance is 1 ppm, this means that there is 1 part of that substance for every 1 million parts of the solution. Converting these units to other perspectives: 1 ppm is analogous to 1 cm in 10 km or 30 seconds in a year. In the context of water quality, ppm is often used to report the concentration of pollutants or trace contaminants. For example, the Environmental Protection Agency (EPA) in the United States has determined that the safe level of the fluoride ion in tap water should not exceed 4 ppm to avoid adverse health effects.
Some examples of concentrations in natural water are that rainwater typically contains about 4 ppm of total dissolved solids (TDS), river water about 120 ppm, and seawater about 35,000 ppm. To convert concentration from ppb (parts per billion) to ppm, we use the fact that 1 ppm equals 1000 ppb. For example, if we have a contaminant concentration of 21 ppb, this is equivalent to 0.021 ppm.