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Extension Toxicology Network

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.


Publication Date: 9/93


Persons interested in the issues surrounding exposure to pesticides (or other chemicals) in either the occupational or environmental context find that exposure levels are expressed in relation to some standard. Unless the individual is familiar with both the science of the chemical and the regulatory process the meaning is often not apparent, particularly when the standard is referred to by its acronym. This compilation is intended to be of assistance by identifying the acronym and providing a definition.

  1. Acronyms and Terms:

    Action Level
    The level of exposure at which certain provisions of the standards must be initiated, such as periodic measurements of employees, and medical surveillance (if appropriate for the particular substance.)

    ADI, Acceptable daily intake
    An estimate of acceptable daily dietary exposure which is derived from a no observed effect level (NOEL) and a safety factor.

    BEI, Biological exposure indices
    A measure of the amount of chemical absorbed into the body.

    CFR, Code of federal regulations
    A codification of the general and permanent rules published in the Federal Register by the Executive departments and agencies of the Federal Government.

    Any physical, chemical, biological, or radiological substance in water.

    DWEL, Drinking water equivalent level
    The medium-specific exposure which is interpreted to be protective for non-carcinogenic end-points of toxicity over a lifetime of exposure. Medium refers to the substrate, i.e., drinking water, and the standard assumes lOO% of the exposure is from that medium.

    GRGL, Groundwater residue guidance level
    The residue level at which no known or anticipated adverse effects on health of persons may occur, including an adequate margin of safety.

    HA, Health advisory
    Non-regulatory information on health effects, analytical methodology and treatment technology that would be useful in dealing with contamination of drinking water. Developed from data describing non-carcinogenic end- points of toxicity.

    HERP, Human exposure dose/rodent potency dose
    Index of possible hazard where human exposure (daily lifetime dose in mg/kg) is expressed as a percentage of the rodent TD50 (toxic dose affecting 50% of the population) dose (in mg/kg) for a given carcinogen.

    IDLH, Immediately dangerous to life and health
    Represents a maximum concentration from which, in the event of respirator failure, one could escape within 30 minutes without experiencing any escape-impairing or irreversible health effects.

    LEL, Lowest effect level
    (See LOAEL)

    LOAEL, Lowest-observed-adverse-effect level
    (also LEL and LOEL) In a series of dose levels tested, it is the lowest level at which an effect (adverse) is observed in the species tested.

    LOEL, Lowest-observed-effect level
    (See LOAEL)

    MAC, Maximum allowable concentrations
    Used in industrial toxicology to define permissible levels of exposure to chemicals.

    MCL, Maximum contaminant level
    The maximum permissible level of a contaminant in water which is delivered to any user of a public water system. MCL levels take into account feasibility and cost but are set as close as possible to the level at which no adverse health effects occur.

    MCL Goal, Maximum contaminant level goal
    The level at which no known or anticipated adverse effects on the health of persons occur and which allows an adequate margin of safety. MCL goals and MCLs for each contaminant must be set simultaneously. RMCLs set prior to 1986 now are treated as MCL goals.

    MPC, Maximum permissible concentration
    Used to recommend maximal levels of uranium compounds in drinking water.

    MRL, Minimal Risk Level
    An estimate of daily human exposure to a chemical that is likely to be without an appreciable risk of deleterious effects (noncancerous) over a specified duration of exposure.

    NEL, No-effect level
    (See NOAEL)

    NOAEL, No-observed-adverse-effect-level
    (also NEL, NOEL) In a series of dose levels tested, it is the highest level at which no effect is observed, i.e., safe, in the species tested.

    NOEL, No-observed-effect-level
    (See NOAEL)

    PEL, Permissible exposure limit
    An OSHA standard which is subject specific and has the supporting documentation for promulgation and enforcement of occupational health regulations. An allowable exposure level in the workplace air averaged over an eight-hour shift.

    PHI, Preharvest interval
    The period between the last application of a pesticide and harvest of the crop.

    Q*, Oncogenic potency
    Potency factor derived from mathematical models that extrapolate from data derived from animal experiments to estimate human cancer risk. The Q* value is a probabilistic estimate of the upper bound on incidence of extra instances of tumor formation in humans that can be expected following dietary ingestions, or exposure by other routes, of a given level of a particular chemical over a 70-year human lifetime.

    RDA, Recommended dietary allowance
    National Academy of Science allowance intended to provide for individual variations among most normal persons as they live in the United States under usual environmental stress.

    RfD, Reference Dose
    An estimate (with uncertainty spanning perhaps an order of magnitude) of the daily exposure of the human population to a potential hazard that is likely to be without risk of deleterious effects during a lifetime. The RfD is operationally derived from the NOAEL (from animal and human studies) by a consistent application of uncertainty factors that reflect various types of data used to estimate RfDs and an additional modifying factor, which is based on a professional judgment of the entire database on the chemical. The RfDs are not applicable to nonthreshold effects such as cancer.

    RMCL, Recommended maximum contaminant level
    RMCLs are set by rule for any contaminant in drinking water which may adversely affect the health of persons. RMCLs are set at a level at which no known or anticipated adverse health effects occur with an adequate margin of safety. RMCLs set prior to MCLs for each contaminant. Note: the term RMCL was replaced by the term "MCL goal" in the Safe Drinking Water Act Amendments of 1986.

    RRfD, Risk reference dose
    Estimate of daily exposure to the human population which appears to be without appreciable risk of deleterious effects over a lifetime of exposure.

    SIC, Surveillance index classification
    Five classifications used by FDA to categorize health hazards.
    Class I _ high health hazard on a toxicological basis.
    Class II _ evidence of possible high risk of toxic effects.
    Class III _ moderate profile based on weighing both toxicity and
    dietary exposure factors.
    Class IV _ low hazard potential, justifies only intelligence related monitoring effects.
    Class V _ little potential hazard due to low toxicity or minimal possible exposure.

    SNARL, Suggested no adverse response level
    A level protective of a 70 kg adult consuming 2 liters of water per day and for whom drinking water is assumed to contribute 20% of the daily exposure to the chemical residue.

    TADI, Temporary acceptable daily intake
    (See ADI)

    TAS, Tolerance Assessment System
    The TAS joins pesticide-commodity tolerance data with food consumption data to estimate possible chemical intake levels.

    TLV, Threshold limit value
    Refers to airborne concentrations of substances and represents conditions under which it is believed that nearly all workers may be unaffected.

    TLV-C, Ceiling
    The concentration that should not be exceeded during any part of the working exposure.

    TLV-STEL, Short term exposure limit
    Supplements the TWA where there are recognized acute effects from a substance whose toxic effects are primarily of a chronic nature. A 15- minute TWA not to be exceeded at any time.

    TLV-TWA, Time weighted average
    (based on up to a lO-hour exposure unless otherwise noted) Concentration for a normal 8-hour workday and a 40-hour workweek to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.

    TMRC, Theoretical maximum residue contribution
    The amount of a substance that would be present in a 1.5 kg "average" daily diet if all commodities with established tolerance bore residues at the tolerance level. EPA assumes that (l) each pesticide is used on all harvested crop acres for which a tolerance exists or is proposed and (2) pesticide residues are present at full tolerance levels in every food consumed.

    TMRL, Temporary maximum residue limit
    (See MRL)

    A legal limit, currently established by EPA, for the maximum amount of a pesticide residue which may be present in or on a food.

    UCR, Unit cancer risk
    The result of applying linear models to carcinogenicity data to estimate the upper limit on lifetime risk per unit of dose. Specific properties of substances are generally not taken into account.

    UF, Uncertainty factor
    A factor used in operationally deriving the RfD from experimental data. UFs are intended to account for (l) the variation in sensitivity among the members of the human population, (2) the uncertainty in extrapolating animal data to the case of humans, (3) the uncertainty in extrapolating from data obtained in a study that is of less than lifetime exposure, and (4) the uncertainty in using LOAEL data rather than NOAEL data. Usually each of these factors is set equal to 10.

  2. Comparison of EPA and IARC Classification Systems for Evidence of Carcinogenicity

    1. Assessment of Evidence from Human Studies:

      EPA IARC
      1. Sufficient Evidence
      2. Limited Evidence
      3. Inadequate Evidence
      4. No Data
      5. No Evidence
      1. Sufficient Evidence
      2. Limited Evidence
      3. Inadequate Evidence

    2. Assessment of Evidence from Experimental Animals:

      EPA IARC
      1. Sufficient Evidence
      2. Limited Evidence
      3. Inadequate Evidence
      4. No Data
      5. No Evidence
      1. Sufficient Evidence
      2. Limited Evidence
      3. Inadequate evidence
      4. Negative Evidence
      5. No data

    3. Categorization of Evidence for Human Carcinogenicity

      EPA IARC
      1. Group A, Human Carcinogen
      2. Group B, Probable Human Carcinogen
        1. B1
          1. Limited epidemiologic evidence
          2. Sufficient animal studies
        2. B2
      3. Group C, Possible Human Carcinogen
      4. Group D, Not Classifiable
      5. Group E, Evidence of Non-carcinogenicity for Humans
      1. Group 1, Carcinogenic for Humans
      2. Group 2, Probably Carcinogenic for Humans
        1. 2A
          1. Human evidence almost sufficient
          2. Animal data sufficient
        2. 2B
      3. Group 3, Not Classfiable