1 of 15

pesticide.pes

The pesticide database summarizes parameters used by the model to simulate the fate and transport of different types of pesticides.

Field

Description

Type

Unit

Default

Range

name (pesticide.pes)

Name of the pesticide record

The name of the urban land type is a primary key referenced when pesticide applications are scheduled in or . All names in the pesticide.pes database must be unique.

Name

Description

soil_ads

Soil adsorption coefficient normalized for soil organic carbon content

Pesticides in the soil environment can be transported in solution or attached to sediment. The partitioning of a pesticide between the solution and soil phases is defined by the soil adsorption coefficient for the pesticide. The soil adsorption coefficient is the ratio of the pesticide concentration in the soil or solid phase to the pesticide concentration in the solution or liquid phase:

$K_p=\frac{C_{solidphase}}{C_{solution}}$

where $K_p$ is the soil adsorption coefficient ((mg/kg)/(mg/L) or m3/ton), $C_{solidphase}$ is the concentration of the pesticide sorbed to the solid phase (mg chemical/kg solid material or g/ton), and $C_{solution}$ is the concentration of the pesticide in solution (mg chemical/L solution or g/ton). The definition of the soil adsorption coefficient in this equation assumes that the pesticide sorption process is linear with concentration and instantaneously reversible. Because the partitioning of pesticide is dependent upon the amount of organic material in the soil, the soil adsorption coefficient input to the model is normalized for soil organic carbon content. The relationship between the soil adsorption coefficient and the soil adsorption coefficient normalized for soil organic carbon content is:

$K_p=K_{oc}*\frac{orgC}{100}$

where $K_p$ is the soil adsorption coefficient ((mg/kg)/(mg/L)), $K_{oc}$ is the soil adsorption coefficient normalized for soil organic carbon content ((mg/kg)/(mg/L) or m3/ton), and $orgC$ is the percent organic carbon present in the soil.

frac_wash

Fraction of pesticide on foliage that is washed off by rainfall event

The wash-off fraction is a function of the nature of the leaf surface, plant morphology, pesticide solubility, polarity of the pesticide molecule, formulation of the commercial product and timing and volume of the rainfall event.

hl_foliage

Half-life of the pesticide on the foliage

The half-life for a pesticide defines the number of days required for a given pesticide concentration to be reduced by one-half. The half-life entered for a pesticide is a lumped parameter that includes the net effect of volatilization, photolysis, hydrolysis, biological degradation and chemical reactions.

For most pesticides, the foliar half-life is much less than the soil half-life due to enhanced volatilization and photodecomposition. If the foliar half-life is available for the pesticide this value should be used. If the foliar half-life is not available, the foliar half-life can be estimated using the following rules:

Foliar half-life is assumed to be less than the soil half-life by a factor of 0.5 to 0.25, depending on vapor pressure and sensitivity to photodegradation.
Foliar half-life is adjusted downward for pesticides with vapor pressures less than 10-5 mm Hg.
The maximum foliar half-life assigned is 30 days.

hl_soil

Half-life of the pesticide in the soil

The half-life for a pesticide defines the number of days required for a given pesticide concentration to be reduced by one-half. The soil half-life entered for a pesticide is a lumped parameter that includes the net effect of volatilization, photolysis, hydrolysis, biological degradation, and chemical reactions.

solub

Solubility of the pesticide in water

The water solubility value defines the highest concentration of pesticide that can be reached in the runoff and soil pore water. While this is an important characteristic, researchers have found that the soil adsorption coefficient, , tends to limit the amount of pesticide entering solution so that the maximum possible concentration of pesticide in solution is seldom reached. Reported solubility values are determined under laboratory conditions at a constant temperature, typically between 20°C and 30°C.

aq_reac

Aquatic pesticide reaction coefficient

aq_volat

Aquatic volatilization coefficient

mol_wt

Molecular weight to calculate mixing velocity

aq_resus

Aquatic resuspension velocity for pesticide sorbed to sediment

aq_settle

Aquatic settling velocity for pesticide sorbed to sediment

ben_act_dep

Depth of the active benthic layer

ben_bury

Burial velocity in the benthic sediment

ben_reac

Reaction coefficient in the benthic sediment

soil_ads

Soil adsorption coefficient normalized for soil organic carbon content

$K_p=\frac{C_{solidphase}}{C_{solution}}$

$K_p=K_{oc}*\frac{orgC}{100}$