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Toxic Chemicals
• Ingestion carcinogenicity
• Inhalation carcinogenicity
• Ingestion noncarcinogenic toxicity
• Inhalation noncarcinogenic toxicity
The toxicity information was downloaded from the USEPA human health-based
risk assessment Web address at the time this book was written (USEPA 2009).
INGESTION CARCINOGENICITY
We based our assessment of ingestion carcinogenicity, that is, cancer risk due to
ingestion of a chemical, on the oral slope factor (SFO) of the USEPA. The SFO is
expressed as inverse of dose (milligram of compound per kilogram of body mass
per day) −1 and represents the proportion of a population that is estimated to develop
increased cancer risk if each individual were to ingest 1 mg of a chemical per
kilogram of their body weight each day over a lifetime (upper-bound estimate). The
higher the SFO is, the higher will be the cancer risk from a particular chemical relative to a chemical that has a lower SFO. The SFO is generally reserved for use in the
low-dose region of the dose-response relationship (i.e., for exposures corresponding
to risks less than 1 in 100).
For example, a chemical with an SFO of 11 (mg/kg-day) −1 represents 11 extra
cancer cases per person ingesting 1 mg of a chemical per kilogram body mass per day.
An SFO of 1 × 10 −2 (mg/kg-day) −1 represents 1 excess cancer case per 100 people
ingesting 1 mg of the chemical per kilogram body mass per day.
INHALATION CARCINOGENICITY
We based our assessment of inhalation carcinogenicity, that is, cancer risk due to
inhalation of a chemical, on the inhalation unit risk (IUR) number of the USEPA.
The IUR, expressed in units of (microgram/cubic meter) −1 , represents an upper-bound
excess lifetime cancer risk estimated to result from continuous exposure to a chemical at a concentration of 1 μg/m 3 of air. The higher the IUR is, the higher the cancer
risk from a particular chemical will be relative to a chemical that has a lower IUR.
For example, if the IUR of a chemical equals 3 × 10 −6 (μg/m 3 ) −1 , 3 excess cancer
cases are expected to develop per 1 million people if exposed daily for a lifetime
to 1 μg of the chemical per cubic meter of air. An IUR of 38 (μg/m 3 ) −1 represents
38 extra cancer cases per person inhaling 1 μg of the chemical per cubic meter of air
for a lifetime.
INGESTION NONCARCINOGENIC TOXICITY
We based our assessment of ingestion noncarcinogenic toxicity, that is, noncancer
risk due to ingestion of a chemical, on the oral reference dose (RfDo) of the USEPA,
which is an estimate (with uncertainty spanning perhaps an order of magnitude) of
a continuous oral exposure to the human population (including sensitive subgroups)
that is likely to be without an appreciable risk of deleterious effects during a lifetime.