Each route poses different potential risks following exposure because distribution throughout the body occurs differently. Only compounds that can pass through the skin pose any risk from dermal exposure. Only gases, vapors or very small particles will reach the lungs and pose a risk via inhalation. The relative importance of the different routes will change depending on the contaminant. One route of exposure is not always more or less toxic than another.
Uncertainties Often point estimates of toxicity or exposure are used in risk assessments.
If individuals or species vary widely in their sensitivity to one or more contaminant within a comparative risk assessment, a point estimate for toxicity may misrepresent the relative toxicity for those contaminants and species. It may be important to consider the overlap of the results for the toxicity tests conducted for each contaminant before ranking which is more toxic. For each taxonomic group included, risk factors need to be evaluated, and each contaminant assigned a rank according to how that factor contributes to potential risk. A factor could be assigned a rank of zero if that factor precludes the possibility of risk. The final comparison may be performed by multiplying the ranks to determine which contaminant poses the greatest overall risk.