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IDLH
Immediately dangerous to life and health. Used to determine selection of a respirator. The maximum concentration from which one could escape within 30 minutes without any escape-impairing symptoms or irreversible health effects. Also, IDLH conditions and conditions that would lead to an IDLH exposure.
World Health Organization (WHO)
WHO, an agency of the United Nations, carries out public and environmental health programs throughout the world.
Maximum Contaminant Level (MCL)
The highest (maximum) level of a contaminant allowed to go uncorrected by a public water system under federal or state regulations. Depending on the contaminant, allowable levels might be calculated as an average over time, or might be based on individual test results.
Latency period
The period of time between exposure to something that causes a disease and the onset of the health effect. Cancer caused by chemical exposure may have a latency period of 5 to 40 years.
Gradient
The change in a property over a certain distance. For example, lead can accumulate in surface soil near a road due to automobile exhaust. As you move away from the road, the amount of lead in the surface soil decreases. This change in the lead concentration with distance from the road is called a gradient.
Superfund (federal and state)
The federal and state programs to investigate and clean up inactive hazardous waste sites.
Aquifer
An underground source of water. This water may be contained in a layer of rock, sand or gravel.
Quality assurance and quality control (QA/QC)
A system of procedures, checks and audits to judge and control the quality of measurements and reduce the uncertainty of data. Some quality control procedures include having more than one person review the findings and analyzing a sample at different times or laboratories to see if the findings are similar.
Material Safety Data Sheet (MSDS)
A compilation of information required under the OSHA Communication Standard on the identity of hazardous chemicals, health, and physical hazards, exposure limits, and precautions. Section 311 of SARA requires facilities to submit MSDSs under certain circumstances.
Concentration
Any substance that enters a system (the environment, human body, food, etc.) where it is not normally found. Contaminants are usually referred to in a "negative" sense and include substances that spoil food, pollute the environment or cause other adverse effects.
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