Toxic Pollutants, Measuring

The amount of pollution in our environment continues to pose a challenge for industry, business, and decisionmakers. Some of the major chemicals of concern are those that harm the environment on a large scale, such as chlorofluorocarbons, which destroy the atmospheric ozone layer. Other chemicals that are harmful to human health are lead in water, cyanide (a deadly poison) leaching from landfills into water supplies, ammonia from car exhaust, and a long list of carbon-based chemicals that are byproducts of industrial processes.

Pollutants may start out as a solid, liquid, or gas, but eventually are counted as individual molecules within another substance. For instance, if a contaminant contains many toxic chemicals, each one will be measured separately. Some chemicals are more toxic to living organisms than others, so they are measured independently to discover their presence in the environment.

A toxic substance is usually measured in "parts per million" or "ppm." This measure states that the number of units of the particular chemical under survey occurs in comparison to one million units of the surrounding natural chemicals. When amounts of toxic chemicals are measured over large areas over a specific period of time, the amounts of pollutants can be measured in pounds.

Categories of Toxic Pollutants

Identifying dangerous wastes can be a complicating factor in measuring certain pollutants. There are four major categories of toxic pollutants that cover a wide range of materials.

The first major grouping of pollutants is based on ignitability, or its ability to catch on fire or explode. These are wastes and pollutants that may be a fire hazard if they collect in landfills or other storage sites. Liquids and solids are not usually ignitable, but the vapors or fumes they make can be very dangerous. Each type of ignitable pollutant has a flash point. The flash point is the temperature at which the flammable vapors will interact with a spark or flame to create an explosion. Each pollutant has its own flash point which has been determined in a laboratory.

Another measure of toxic chemicals is their corrosivity, which is a chemical process in which metals and minerals are converted into undesirable byproducts. One of the ways in which corrosiveness is measured is by the pH, which is an indicator of the acidity or alkalinity of solution.

Mathematically, pH is the negative logarithm of the hydrogen ion (a single proton with no electron) concentration in water. The pH scale ranges from 1 to 14. A pH of between 1 and 3 is highly acidic while values between 11 and 14 indicate a highly alkaline solution. A pH of 7 is considered neutral.

The third general category of pollutants is based on the reactivity of the substance. Reactive chemicals are identified as pollutants because they may explode or make toxic fumes that pose a threat to human health and the environment. Soils are often acidic or basic, so the potential reactivity of chemicals in soils is of great concern. Among other properties, reactive pollutants:

• readily undergo violent chemical change;
• react violently or form potentially explosive mixtures with water; and
• generate toxic fumes when exposed to mildly acidic or basic conditions.

The last of the four general categories of toxic pollutants is based on the toxicity of substances. Toxicity is the ability of a substance to produce adverse health effects by exposure to the substance.

Measuring Toxic Pollutants

An example of how some pollutants are measured, including ignitable and toxic substances, is the Toxicity Characteristic Leaching Procedure (TCLP). This procedure and others, sometimes called Extraction Procedures (EP), are based on how a leaching pollutant may decompose and distribute to the water supply or soil from a landfill containing city solid waste. The major concern about the leaching process is the possibility that toxic chemicals may reach the groundwater and migrate to other sources of drinking water.

There are numerous chemical processes used to obtain a sample for analysis. These are many stepped (phased) processes and all have very clear guidelines on how they are to be performed. Once the TCLP extract has been obtained it is immediately tested for pH. All individual chemicals are analyzed separately. The initial analysis starts with the following formula:

where

V1 = volume of the first phase (L)

C1 = concentration of the analyte of concern in the first phase (mg/L)

V2 = volume of the second phase (L)

C2 = concentration of the analyte of concern in the second phase (mg/L).

To assure quality control over of initial measurements there are many additional mathematical and chemical measurement techniques that are performed after the first analysis. In one type of quality control one in every 20 samples is remeasured. This particular sample is called spike. It is measured against a sample without the potential toxin in it (the control). The spikes are calculated by the following formula:

Percent R (percent recovery) 100 = (X_s - X_u)/K

where

X_s = measured value for the spiked sample

X_u = measured value for the unspiked sample

and

K = known of the spike in the sample (this comes from the first or known measurement of the sample).

see also Logarithms.

Brook E. Hall

Bibliography

Washington State Department of Ecology. Washington State Toxics Release Inventory: Summary Report 1997. Washington State, 1999.

Washington State Department of Ecology. Reducing Toxics in Washington: A Report to the Legislature. Washington State, 1999.

Washington State Department of Ecology. Biological Testing Methods 80-12 for the Designation of Dangerous Waste. Washington State, 1999.