The toxicity assessment quantifies the sensitivity of the receptor to the chemical hazard. In a Preliminary Quantitative Risk Assessment, the toxicity assessment typically consists of choosing the correct toxicity reference value (TRV) for a given contaminant and exposure uptake route. TRVs generally can be used for multiple routes of exposure (i.e., dietary, inhalation or dermal contact), but for some contaminants, separate TRVs are provided specifically for ingestion and inhalation pathways.
Toxicity assessments consider the mode of action of the contaminant, the toxic potency as observed in scientific studies, and physiological/biochemical factors which might modify the toxic potency.
Generally, chemicals are considered to have either a threshold or non-threshold dose or concentration where toxic effects may begin to occur. Each is assessed differently in a human health risk assessment (Health Canada 1994).