Drinking Water in Germany: A Case Study of High Quality Drinking Water - Global Drinking Water Management and Conservation - page 264

threshold of concern. The probability of human intake at this threshold level (i.e.
TTC of 0.15 mg per person per day) is 86 to 97 percent, but the cancer risk would
be less than 1 10 − 6 (or 0.000001) (Kroes et al. 2004 ). Mons et al. ( 2013 ) noted

that although the TTCs of compounds below the Cramer class III were observed
frequently, effects observed at doses below those related to the TTC of 1.5 mg per
day per person have not been reported. Therefore,

×

“ this value appears to be suffi- -

ciently protective and it is regularly reviewed with the latest knowledge and data ”

(Mons et al. 2013 ).
However, it should be noted that according to the European Food Safety
Authority ( 2012 ), the TTC approach is not to be applied to (a) high potency
carcinogens atoxin-like, azoxy- or N-nitroso-compounds, benzidines,

hydrazines), (b) inorganic substances, (c) metals and organometallics, (d) proteins,
(e) steroids, (f) substances that are known or predicted to bioaccumulate, and (g)
nanomaterials. These must be treated separately as they are dangerous to human
health.

(i.e. a

12.5.1.2 Target Values

Using the TTC approach, the target values for micropollutants which are anthro-
pogenic drinking water contaminants, can be determined. The proposed target
values are summarized in Table 12.2 . The target values for individual genotoxic and
steroid endocrine chemicals were set at 0.01 mg/L. For all other organic chemicals
the target values were set at 0.1 mg/L. The target values for the total sum of
genotoxic chemicals, the total sum of steroid hormones, and the total sum of all
other organic compounds were set at 0.01, 0.01, and 1.0 mg/L, respectively.
However, there are two concerns about target values for organic contaminants in
drinking water. First, many different compounds can be present individually in

drinking water at concentrations below the target values, but as a mixture, the sum
of all compounds together might still threaten human health

“

” (European Com-

mission 2009). Therefore, there is justi cation for setting a target value for the sum

of all contaminants, to avoid the presence of a wide variety of compounds at

levels just below their individual target value

“…

” (Mons et al. 2013 ). Moreover,

Table 12.2 Proposed target
values for organic
contaminants in drinking
water in the Netherlands
(Mons et al. 2013 )

Compound group Target value

(mg/L)

Single genotoxic organic chemicals 0.01

Single (synthetic) steroid hormones 0.01

All other single organic chemicals 0.1

Total sum of genotoxic compounds 0.01

Total sum of (synthetic) steroid hormones 0.01

Total sum of all other organic chemicals 1