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Chemical Hazard Evaluation for Management Strategies

Chemical Hazard Evaluation for Management Strategies

Introduction :

Mary Swanson led a group of researchers who designed the CHEMS 1 environmental indicator model. This model assesses potential risk with a ranking methodology that calculates hazards to human health and the environment. The model considers the environmental impact of chemicals on air, soil, groundwater, and surface water. It examines such factors as the chemical's propensity to cause abnormal effects in mammals and how much of the chemical is already present in the environment because of industrial uses.


  • Swanson, M., Davis, G., Kincaid, L., Schultz, T., Bartmess, J., Jones, S., George, E., 1997. A screening method for ranking and scoring chemicals by potential human health and environmental impacts. Environmental Toxicology and Chemistry 16 (2), 372-383.

Equations :

To arrive at an assessment of risk the CHEMS 1 model calculates hazard values for a variety of variables in three separate sections: human health effects, environmental effects, and exposure factor. These sections are then incorporated in equation (1) which calculates a total hazard value.

  1. Total hazard value = (human health effects + environmental effects)*exposure factor
    For each variable in each section, a ranking methodology is used to score chemical hazard values based on certain toxicity information and chemical parameter information. These values are then added to arrive at hazard values for the specific sections. Then, these hazard values can be multiplied by a "release weighting factor" that takes into account how much of the pesticide is already in the environment.

  2. Human Health Effects = HVor + HVinh + HVcar + HVnc
    HVor = 6.2 - 1.7(logLD50) for 5mg/kg < LD50 £ 5000 mg/kg
    = 0 for LD50 > 5000 mg/kg
    = 5 for LD50 £ 5 mg/kg

    HVinh = 8.0 - 2.0(log LC50) for 31.6 ppm £ LC50 £ 10000 ppm
    = 0 for LC50 > 10000 ppm
    = 5 for LC50 < 31.6 ppm

    (Note: LD50 and LC50 values are from rats)

    HVcar = 0 for Group E EPA carcinogen class
    = 0 for Group D EPA carcinogen class
    = 1.5 for Group C EPA carcinogen class
    = 3.5 for Group B2 EPA carcinogen class
    = 4.0 for Group B1 EPA carcinogen class
    = 5.0 for Group A EPA carcinogen class

    HVnc = Mutagenic Effects + Developmental Effects + Reproductive Effects + Neurotoxic Effects
    (Note: for each effect present a score of 1 is assigned. If no effect is present, a score of 0 is assigned).

  3. Environmental Effects = HVmam + HVfa + HVfc
    HVmam = 6.2 - 1.7(logLD50) for 5mg/kg < LD50 £ 5000 mg/kg
    = 0 for LD50 > 5000 mg/kg
    = 5 for LD50 £ 5 mg/kg
    (Note: LD50 values are from rats)

    HVfa = -1.67(logLC50) + 5.0 for 1 mg/L £ LC50 < 1000 mg/L
    = 0 for LC50 ³ 1000 mg/L
    = 5 for LC50 < 1 mg/L
    (Note: LC50 values are from fish)

    HVfc = 3.33 - 1.67(log NOEL) for 0.1 mg/L < NOEL £ 100 mg/L
    = 0 for NOEL > 100 mg/L
    = 5 for NOEL £ 0.1 mg/L
    (Note: NOEL values are from fish).

  4. Exposure Factor = HVbod + HVhyd + HVbcf
    HVbod, hyd = 1 for hydrolysis half-life £ 4 days
    = 2.5 for hydrolysis half-life > 500 days
    = 0.311(LN hydrolysis half-life) + 0.568
    for 4 days < hydrolysis half-life £ 500 days

    HVbcf = 0.5(log BCF) + 0.5 for 1.0 < log BCF £ 4.0
    = 1 for log BCF £ 1.0
    = 2.5 for log BCF > 4.0

  5. Release-Weighted Hazard Values
    For active ingredients already released.
    RWF = LN (chemical releases) - 10

    For pesticide applications
    RWF = LN(actual application rate) +A
    = 1 for actual application rate < B
    A = 10 - LN (Maximum application rate)
    B = e(1-A)

    wHVor = (HVor)(RWFw)
    wHVinh = (HVinh)(RWFa)
    wHVcar = (HVcar)(RWFt)
    wHVnc = (HVnc)(RWFt)
    wHVmam = (HVmam)(RWFw)
    wHVfa = (HVfa)(RWFw)
    wHVfc = (HVfc)(RWFw)

List of Symbols :

Description & Units
actual application rate lbs/acre of active ingredient applied
chemical releases lbs of chemical already in the environment
HVbcf hazard value for aquatic bioconcentration
HVbod hazard value for biodegradation
HVcar hazard value for carcinogenicity
HVfa hazard value for acute toxicity to fish
HVfc hazard value for chronic toxicity to fish
HVhyd hazard value for hydrolysis degradation
HVinh hazard value for acute inhalation toxicity
HVmam hazard value for acute oral toxicity for mammals
HVnc hazard value for chronic, non-cancer toxicity
HVor hazard value for acute oral toxicity
maximum application rate maximum amount of active ingredient recommended for a growing season according to the pesticide's label (lbs/acre)
RWFw release weighting factor for water
RWFa release weighting factor for air
RWFt total release weighting factor

Analysis :

In order to use CHEMS1 at the farm level, assumptions have to be made. First, it has to be assumed that CHEMS1 could be used on the smaller scale of a farm field since it was specifically designed to assess the effects of large amounts of chemicals already in the environment due to industrial production. To accomplish this, the way the model takes into account how much pesticide is already in the environment has to be adjusted to reflect the smaller amounts of chemicals typically seen on the farm level. This adjustment is observed in the pesticide application section of Equation (v) and was suggested by Mary Swanson, one of the authors of the CHEMS1model. Second, the model requires the use of "biological oxygen demand half lives." These values can be difficult to determine and may have to be left blank when using this model at the farm level.


American Farmland Trust