Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 485

C dw Q dw
BW

E dw = (11.49)

in which

E dw = the exposure due to consumption of drinking water

kg body weight − 1 d − 1 ]

[mg · ·

L − 1 ]

C dw = the contaminant concentration in the drinking water [mg ·

d − 1 ]

Q dw = the average daily consumption of drinking water [L ·

BW = the body weight [kg]

Since exposure is often calculated for different age groups, age dependent
consumption rates and body weights may be needed.

11.4.2.2 Inhalation of Volatilised Domestic Water
In the US EPA Preliminary Clean-up Goals (US EPA 1991 ) volatilisation from all
uses of household water is considered (e.g., showering, laundering, dish washing).
An empirical expression is used for the relationship between the concentration of
a contaminant in household water and the average concentration of the volatilised
contaminant in air (Andelman 1990 ). This is based primarily on experimental data
on the volatilization of radon from domestic water. The equation uses a default
“volatilization” constant (K) upper-bound value of 0.5 mg m − 3 per mg L − 1 .It
is assumed that the volume of water used in a residence for a family of four is
720 L.d − 1 , the volume of the dwelling is 150 m 3 and the air exchange rate is
0.25 m 3 h − 1 . Furthermore, it is assumed that the average transfer efficiency
weighted by water use is 50% (i.e., half of the concentration of each contaminant
in water will be transferred into air by all water uses, the range reported to be from
30% for toilets to 90% for dishwashers).
Special models have been developed for evaluating the evaporation rate of the
volatile contaminants during showering by calculating the mass transfer in the
boundary layer between the shower water drops and the surrounding air using
two-film theory (Foster and Chrostowski 1986 ; Little 1992 ). The mass transfer is
dependent on the drop size, the fall time of the droplet, the temperature corrected
Henry's Law constant and a contaminant specific mass transfer resistance. The mass
transfer resistance takes into account the resistance in the water boundary layer of
the drop and the air boundary layer surrounding the drop. This type of model is
included in the Dutch (CSOIL) and Flemish models (Vlier-Humaan) used for the
derivation of Soil Quality Standards.

11.4.2.3 Dermal Contact During Showering

Dermal uptake of contaminants while bathing or showering is modelled using a
dermal absorption rate or dermal permeability coefficient. These can either be based
on empirical data or derived from empirical relationships using the octanol-water