Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 469

11.3.2 Mathematical Equations

11.3.2.1 Calculation of Animal Intake

Animal intake through food, water and soil ingestion are summed up, as follows:

I a = Q a , j × C j + Q a , s × C s × B s + Q a ,water ×

C water (11.4)

j

in which

I a = daily contaminant intake of the animal [mg/d]

Q a,j = quantity of plant j grown on the contaminated site and ingested by the

animal [kg/d]
C j =

concentration of contaminant in plant j [mg/kg dw ]
Q a,s =

quantity of soil ingested by the animal [kg/d]

C s = average concentration of contaminant in soil [mg/kg dw ]

B s = relative oral bioavailability [-] in the body of the animal of the contaminant

in soil. B s is the absolute oral bioavailability in the body of the animal of the
soil contaminant divided by the bioavailability of the contaminant in food or
water. As for humans, B s is used, because soil contaminants are assumed to
be less bioavailable than the same contaminants ingested with food or water.
Q a, water = quantity of water ingested by the animal [l/d]

C water = concentration of contaminant in water [mg/L]

To follow the variations of the contaminant concentrations in animal products for
an annual cycle, animal intake needs to be defined as a function of time. However,
within the framework of an evaluation of chronic risks (from one to several years
of exposure), the average intake by animals over the exposure duration is often
sufficient.
The relevant fodder items will depend on the specific situation at the contami-
nated site and the conditions of breeding. To assess the accumulated concentration
in the animal tissue that originates from the contaminated site, only the fraction of
the total dietary intake of the animals (plants) which is grown on the contaminated
site and the water impacted by site contamination needs to be considered in the
animal diet. In order to assess the total concentration in animal tissue, intake from
background should be added.

11.3.2.2 Calculation of the Concentration of Contaminant in Animal Products

Steady-State Approaches

The most common approach consists in multiplying the animal intake by a bio-
transfer factor (the ratio of animal tissue concentration and the daily intake by the
animal):

C a , i = I a × B Ta , i (11.5)