PRINCIPLES OF TOXICOLOGY

486 EXAMPLE OF RISK ASSESSMENT APPLICATIONS
TABLE 19.4 Example—Worker Exposure to Diesel Fuel Hydrocarbons in Soil, Calculated Hazard
Quotients for Ingestion and Dermal Exposure
HI for decreased body weight = sum of the oral and dermal HQs for aromatic petroleum fraction
C>12–C16 = 0.026
HI for kidney toxicity = sum of the oral and dermal HQs for aromatic petroleum fractions C>16–C21
and C>21–C35 = 0.42
Interpretation of Risk Assessment Results and Comment
As calculated above, concurrent exposure to relatively high concentrations of diesel fuel–related
petroleum hydrocarbons in soil resulted in calculated hazard indices that are less than one for the
liver toxicity, decreased body weight, and kidney toxicity endpoints. These calculations indicate
that workers exposed to concentrations of these petroleum hydrocarbons in soil would be unlikely
to experience adverse health effects as a result of direct exposure to weathered diesel fuel in soil.
19.5 RISK ASSESSMENT FOR ARSENIC
Hazard Quotient
Chemical Ingestion Dermal
C>12–C16
C>16–C21
C>21–C35
C>12–C16
C>16–C21
C>21–C35
Aliphatic
1.08 × 10 –2
4.40 × 10 –3
1.61 × 10 –3
Aromatic
1.83 × 10 –2
1.52 × 10 –1
1.48 × 10 –1
4.31 × 10 –3
1.76 × 10 –3
6.46 × 10 –4
7.34 × 10 –3
6.07 × 10 –2
5.94 × 10 –2
Risk assessors must consider several important factors when assessing the risks posed by arsenic
exposure. First, the chemical form of arsenic must be considered since toxicity varies with the chemical
species. Inorganic arsenic occurs in either the trivalent [arsenite (As 3+ )] or the pentavalent [arsenate
(As 5+ )] state. Arsenite is more toxic than arsenate and these inorganic forms are more toxic than organic
arsenic compounds. Arsenobetaine is an organic form of arsenic that is also called “fish arsenic” since
it occurs naturally in fish. Arsenobetaine is rapidly excreted in the urine and does not accumulate in
the tissues.
Arsenic in the environment may cycle from one form to another based on the chemical conditions
in soil or water and the activity of microbes. Arsenic may be reduced, oxidized, and methylated or
demethylated under certain environmental conditions, potentially resulting in a mixture of arsenite,
arsenate, and organic forms of arsenic in the environment.
The environmental medium in which arsenic occurs will also affect its absorption from the
gastrointestinal tract. Dissolved arsenic in drinking water is well absorbed from the gastrointestinal
tract. In comparison, as a result of tight binding, arsenic absorption from a mineral or soil matrix will
be decreased relative to absorption from food or water.