Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 355

permitted concentration in the point source. The task is to determine the maximum
permissible concentration in the source.

Risk assessment concept of Case study 4

1 Identification and assessment of water uses.

2 Tracing exposure pathways and parameters and determining the total intake

directly and indirectly from water, from vegetable irrigated and animal products
from animals watered by contaminated water.

3 Calculation of the maximum permissible chloroform concentration in the used

waters (in the compliance point), based on human reference values (for toxic and
carcinogenic effects).

4 Using the transport model tracing back the desired concentration in the compliance

point to the source.

5 Characterizing uncertainties.

Results of the inverse risk assessment for Case 4
1. Water uses and exposures

The human population of the residential area is exposed to the contaminant through
drinking water consumption, and the consumption of egg, meat and milk of animals
watered and vegetables irrigated by contaminated water.

2. Exposure parameters
Following the pessimistic approach, the Reasonable Maximum Exposure (RME) is
calculated using the relevant exposure parameters for inhalation in closed room and
during irrigation; ingestion of water as drinking water, or irrigation water; the propor-
tion of contaminated vegetable, milk and meat from the total; daily inhalation from
air, consumption from water, vegetable, egg, milk and meat; frequency and duration
of exposures; body mass and dermal surface. Regarding both humans and animals the
consumed water in total and the contaminated proportion, as well as the absorption
rate of the contaminants from water into the body are important parameters.

3. Calculation of the risk-based screening concentration

The risk-based screening concentrations in the compliance points are calculated as
follows:

RfD ∗ BW ∗ 365 ∗ RCR
IR ∗ EF ∗ AF

LT ∗ BW ∗ 365 ∗ TR
IR ∗ EF ∗ ED ∗ AF ∗ SF

RBSC toxicity = RBSC carcinogenicity =

where

- RfD = reference dose (mg/kg*day)

- BW = body mass (kg)

- RCR = acceptable risk = 1

- IR = water intake rate (L/day)

- EF = exposure frequency (day/year)