4.5. Comparison of intake and concentration-based approaches
Since the intake-based risk assessment method requires reference doses and slope factors, its practical application is more limited than the concentration-based approaches because the intake limits are available mainly for carcinogens.
In the above C2/PA case study, the benchmarks of both methods are exceeded: the 10−4 intake risk benchmark is exceeded for 98.7% of time and the 0.1HTP value for 87% of time in these wind conditions. In this case the intake-based benchmark is stricter.
A question arises on how the benchmarks generally compare. Table 6 presents a comparison of exposure benchmarks for some carcinogenic or potentially carcinogenic chemicals. It is presented to which hazard quotient the 10−4 intake risk benchmark compares and which intake risk the 0.1 hazard quotient corresponds. It can be seen that for these chemicals the risk benchmark for the 0.1HQ concentration is 1.3–25 times larger than the 10−4 benchmark. The results however vary since the occupational exposure limits are often based on different criteria than the slope factors. E.g. formaldehyde exposure limit (HTP) is based on irritation but the slope factor on the carcinogenic effect.