0.15 Air, water and soil  (Page 6/7)

Non-point source pollution is more difficult to regulate than point source emissions. Contamination is measured not at the source, but at the destination. Samples are collected from the air, soil, and water, or from the blood and tissues of organisms in polluted areas. The contribution of various non-point sources to these pollution levels can only be estimated. EPA regulations cannot be directed at specific individuals or businesses and are instead generally directed at municipalities. For example, federal standards are set for allowable levels of chemicals in drinking water, and communities are responsible for treating their water until it meets those standards.

It can be difficult to reduce many types of non-point source pollution because most of the people who contribute to it are not directly faced with legal or financial consequences. Individuals must be persuaded that their activities are causing ecological harm and that they should alter their behavior or spend their money to remedy the situation. Once they do, they may have to wait a long time for noticeable environmental results.

Parts per million (ppm) and micrograms per milliliter (ug/ml)

Very small quantities of some chemicals can have a large impact on organisms. Because of this, substances that are present in trace amounts, such as nutrients and contaminants, are usually measured and recorded using very small units. Two of the most common measures are parts per million and micrograms per milliliter.

Micrograms per milliliter (ug/mL)

Micrograms per milliliter, or ug/mL, measures mass per volume. It is generally used to measure the concentration of a substance dissolved or suspended in a liquid. One microgram is one millionth of a gram (1 ug = 0.0000001 g), and one milliliter is one thousandth of a liter.

Parts per million (ppm)

Parts per million, abbreviated as ppm, is a unitless measure of proportion. It is obtained by dividing the amount of a substance in a sample by the amount of the entire sample, and then multiplying by 106. In other words, if some quantity of gas, liquid, or solid is divided into one million parts, the number of those parts made up of any specific substance is the ppm of that substance. For example, if 1 mL of gasoline is mixed with 999,999 mL of water, the water contains 1 ppm of gas.

Concentration Equivalents

Since a microgram is one millionth of a gram, and a milliliter of water equals one gram of water, ug/mL is equivalent to parts per million. Ppm is also equivalent to many other proportional measurements, including milligrams per liter (mg/L), milligrams per kilogram (mg/Kg), and pounds per acre (lb/acre). But parts per million is often more useful in describing and comparing trace amounts of chemicals because it eliminates specific units and is applicable to liquids, solids, and gases.

Examples

Both ppm and ug/mL can be used to describe the amount of particulate dust in a sample of air:

If the total particulate dust in a one liter volume of air is 5 mg, there is 5 ppm of particulate dust in the air that was sampled, since mg/L (milligrams per liter) = ppm.