2.7 MILK INGESTION


The models for exposure from ingestion of milk are the same as those used for the meat ingestion exposure pathway. The equations are the same as those presented in Subsection 2.6, except that several of the parameters have subscripts changed to indicate the milk pathway is being considered. The following is a summary of the equations for the milk pathway. Only those equations with differences from the meat exposure pathway are presented; unchanged equations are referenced.

For waterborne transport pathways, the transport media, special processes, and exposure factors are as described for the meat ingestion pathway in Subsection 2.6, except that milk instead of meat is ingested by humans.

The application of irrigation water to croplands results in deposition of pollutants to soils and feed crop plants at a constant average rate over the period of irrigation. The deposition rate is given by Equation (18). The soil accumulation factor is also applied to the analysis as given by Equations (19) and (20). The concentration of pollutants in feed-crop plants at the time of feeding to milk animals is evaluated as follows for irrigation deposition onto plants:

(55)



where
and other terms are as previously defined for the leafy vegetable ingestion pathway.

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

(56)



where
and other terms are as previously defined.

    The concentration of pollutants in milk at the time of consumption by humans includes animal intake of feed and water, as follows:

Cmki = FMmki{FCfk [(CWDfki + CWRfki)Qfk + CWSfki Qsk] + Ciri FCwk Qwk } e-lgi TH mk (57)



where
and other terms are as previously defined.

    The average daily dose received by individuals consuming the contaminated milk (for the waterborne transport pathways) is evaluated as follows for chemical pollutants.

(58)



where
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:

(59)

where
and other terms are as previously defined.

    For airborne transport pathways, the milk ingestion exposure evaluation is performed with the same considerations as defined for the meat ingestion pathway of Subsection 2.6.

    The deposition rate from air to plants is given by Equation (26). The soil accumulation factor, as defined by Equations (19) and (20), is also applied to this pathway.

    The concentration of pollutants in feed crop plants is estimated by Equation (55) with parameters for the air pathway substituted for the irrigation pathway, as follows:

(60)

where
and other terms are as previously defined.

    The milk-animal, feed-plant concentration at the time of harvest for uptake from soil via roots is estimated as follows:

(61)



where
and other terms are as previously defined.

    The concentration of pollutants in milk at the time of consumption by humans includes animal intake of feed, as follows:

(62)



where    Cmki = concentration of pollutant i in milk at time of consumption by humans (mg/kg or pCi/kg)

and other terms are as previously defined.

    The average daily dose received by individuals consuming the contaminated milk (for the atmospheric transport pathway) is evaluated using Equation (58) for chemical pollutants. The total lifetime dose is evaluated using Equation (59) for radionuclides.

    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 for the milk ingestion exposure pathway.
Transport Medium:
measured soil at the production location, Cmsi, 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 animal feed plants loss of pollutants from soil by volatilization or decay feeding of crops to animals ingestion of soil by animals loss of pollutants following harvest, prior to consumption of animal products by individuals

Exposure Factors:
rate of animal meat ingestion and exposure duration.

    The evaluation of feed plant concentration eaten by milk animals is performed similarly to the evaluation of vegetable plant concentrations described in the previous sections. The soil average concentration is evaluated using Equation (32), and the plant concentration is evaluated using Equation (33). The animal may also ingest soil. The soil concentration ingested by the milk animal is equal to the average soil concentration given by Equation (32). The concentration in the animal product is evaluated as follows:

(63)



where    
Cfki = concentration in milk animal feed for pollutant i (mg/kg wet weight feed or pCi/wet weight feed)

and other terms are as previously defined.

The average daily intake of chemical pollutants is evaluated using Equation (58), and the lifetime radiation dose for radionuclides is evaluated using Equation (59).