2.5 Other Vegetable Ingestion

2.5 OTHER VEGETABLE INGESTION

    This exposure pathway uses the same model as the leafy vegetable pathway except that parameters may be assigned different numerical values representative of food crops that are not characterized as leafy vegetables. This includes grains, root crops, and crops for which the consumed food is generally not exposed directly to the depositing material. The equations for the other vegetable pathway are the same as those for the leafy vegetable pathway. The equations are repeated here for completeness, with subscripts appropriate to the other vegetable pathway.

    The pollutant deposition rates to croplands from atmospheric transport and irrigation water application are evaluated using the same equations as for the leafy vegetable pathway [Equation (18) for irrigation deposition and Equation (25) for atmospheric deposition]. The soil accumulation factor is also applied to the other vegetables pathway, as defined by Equations (19) and (20).

    When surface water is the source of irrigation water, the correction for loss of pollutant during surface water transport is made as indicated by Equation (3).

    The plant contamination from irrigation deposition onto edible parts of plants will result in a contamination level at harvest that is estimated as follows:

(34)

where

_ovi

_wi

_ov

_ei

_di

^-1

_ov

The plant concentration at the time of harvest for uptake from soil via roots, following irrigation deposition, is estimated as follows:

(35)

where

_ovi

_ov

and other terms are as previously defined.

The concentration in other vegetables is evaluated as the sum of contributions for the two contamination routes: deposition onto plants and root uptake from soil, as follows.

(36)

where

C_ovi = concentration of pollutant i in other vegetables (mg/kg)
l _gi = loss and decay rate constant for pollutant i in closed water systems (d^-1)
TH_ov = holdup time between harvest of other vegetables and consumption by humans (d)
and other terms are as previously defined.

The average daily dose from ingestion of chemical pollutants (for irrigation water contamination) in other vegetables is evaluated as follows:

(37)

where

_ovi

_ov

_ovi

_ov

_ovi

For radioactive pollutants, the total lifetime dose is evaluated as follows:

(38)

where

_ovi

_gi

and other terms are as previously defined.

For the atmospheric deposition pathway, the direct deposition of pollutants from air onto edible parts of plants is estimated by Equation (27), with parameters for the air pathway substituted for the irrigation pathway as follows:

(39)

where

_ovi

_ai

and other terms are as previously defined.

The soil accumulation factor is also applied to the atmospheric deposition to soil route, as defined by Equations (19) and (20). The plant concentration at the time of harvest for uptake from soil via roots following atmospheric deposition is estimated, as follows:

(40)

where

_ovi

_si

(41)

where

_ovi

(42)

where

_ovi

_ov

and other terms are as previously defined. The averaging time for noncarcinogenic chemicals is set to the exposure duration, and the averaging time for carcinogenic chemicals is fixed at 70 years.

For radioactive pollutants, the total lifetime dose is evaluated as follows:

(43)

where D_ovi = total lifetime dose from ingestion of other vegetables (rem)

and other terms are as previously defined.

For the measured soil concentration pathway, the exposure evaluation is performed for an initial soil concentration (measured) with loss and decay during the exposure period. The following considerations are included.

Transport Medium:

measured soil at the production location, C_msi, pCi/kg or mg/kg, expressed as the concentration at the start of the exposure period

Special Process:

uptake by roots from soil to
edible portions of plants
loss of pollutants from soil by volatilization or decay
loss of pollutants following harvest, prior to consumption by individuals

Exposure Factors:

rate of crop ingestion and exposure duration.

The average concentration is evaluated as the time integral of the activity in the soil divided by the exposure duration, as given by Equation (32).

The concentration in edible parts of plants from root uptake from soil is evaluated as follows:

(44)

where terms are as previously defined.

The average daily intake from ingestion of chemicals in leafy vegetables is evaluated using the plant concentration from Equation (44) and intake Equation (42). For radionuclides, the ingestion dose is evaluated using the plant concentration from Equation (44) and dose Equation (43).