Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 341

In summary , the creek's ecosystem is unlikely to be endangered over the short
term to an unacceptable extent. Long-term monitoring of the risk-specific biological
indicators is the proper tool for justifying the 'no risk' situation for the creek's aquatic
ecosystem over the long term. If the groundwater can serve as drinking water, the
decision should be based on human health risk considerations.
Human health risk due to Case study 2 groundwater or surface water use as
drinking water is dominated by benzene cancer risk and toluene toxicity. The risk
calculation of these two chemicals is introduced below.
The daily dose taken in by an adult (D) is calculated as

C w IR ∗ EF ∗ ED
BW ∗ AT

D =

where

- D daily intake in dose (mg/kg*day)

- C w =

=

contaminant concentration in the water (mg/L)

- IR = water intake rate (L/day) (2 L/day)

- EF = exposure frequency (day/year) (350 days/year in this example)

- ED = exposure duration (year) (30 years in this example)

- BW = body mass (kg) (70 kg on average)

- AT average time of exposure (day) (70*365 for benzene carcinogenity and

30*365 for toluene toxicity)

=

0 . 073 ∗ 2 ∗ 350 ∗ 30
70 ∗ 30 ∗ 365

10 − 3 mg / kg D toluene = = 2 . 0 ∗ ∗ day

As a first evaluation step compare the case-specific daily dose to the reference
dose value and calculate the risk characterization ratio (RCR). If RCR < 1, the risk is
acceptable.
Toluene oral intake RfD toluene

=

0.2 mg/kg*day

= =

2.0*10 − 3 /0.2

=

RCR toluene D/Rfd 0 . 01 1, which shows low risk due to

toluene oral exposure.

0 . 029 ∗ 2 ∗ 350 ∗ 30
70 ∗ 70 ∗ 365

3 . 4 ∗ 10 − 4 mg / kg

D benzene = = ∗ day

Benzene is a carcinogenic compound, whose intake has a life-long (70 years) effect
on cancer risk.
Benzene oral slope factor, SF benzene,oral = 0.029 (mg/kg day) − 1 .

=

10 − 5 ; which equals thresh-
old of carcinogenic risk. This calculation indicates that the risk due to benzene oral
intake is within the acceptable limit. If some other, e.g. inhalation risk also exists, the
benzene risk is not acceptable in the greatly pessimistic scenario.
Having validated the transport model, it can be used in an inverse mode starting
from PEC in the compliance point toward the source to determine/estimate either the
emission of the chemical from the source if it is not known, or the target emission
to be reached after risk reduction. This answers the question where the contaminants

10 − 4 10 − 5

Cancer risk = 3 . 4 ∗ ∗ 0 . 029 = 0 . 99 ∗ 1 ∗