PRINCIPLES OF TOXICOLOGY - Biology East Borneo

486 EXAMPLE OF RISK ASSESSMENT APPLICATIONSTABLE 19.4 Example—Worker Exposure to Diesel Fuel Hydrocarbons in Soil, Calculated HazardQuotients for Ingestion and Dermal ExposureHazard QuotientChemical Ingestion DermalAliphaticC>12–C16 1.08 × 10 –2 4.31 × 10 –3C>16–C21 4.40 × 10 –3 1.76 × 10 –3C>21–C35 1.61 × 10 –3 6.46 × 10 –4AromaticC>12–C16 1.83 × 10 –2 7.34 × 10 –3C>16–C21 1.52 × 10 –1 6.07 × 10 –2C>21–C35 1.48 × 10 –1 5.94 × 10 –2HI for decreased body weight = sum of the oral and dermal HQs for aromatic petroleum fractionC >12–C 16 = 0.026HI for kidney toxicity = sum of the oral and dermal HQs for aromatic petroleum fractions C >16–C 21and C >21–C 35 = 0.42Interpretation of Risk Assessment Results and CommentAs calculated above, concurrent exposure to relatively high concentrations of diesel fuel–relatedpetroleum hydrocarbons in soil resulted in calculated hazard indices that are less than one for theliver toxicity, decreased body weight, and kidney toxicity endpoints. These calculations indicatethat workers exposed to concentrations of these petroleum hydrocarbons in soil would be unlikelyto experience adverse health effects as a result of direct exposure to weathered diesel fuel in soil.19.5 RISK ASSESSMENT FOR ARSENICRisk assessors must consider several important factors when assessing the risks posed by arsenicexposure. First, the chemical form of arsenic must be considered since toxicity varies with the chemicalspecies. 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 organicarsenic compounds. Arsenobetaine is an organic form of arsenic that is also called “fish arsenic” sinceit occurs naturally in fish. Arsenobetaine is rapidly excreted in the urine and does not accumulate inthe tissues.Arsenic in the environment may cycle from one form to another based on the chemical conditionsin soil or water and the activity of microbes. Arsenic may be reduced, oxidized, and methylated ordemethylated 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 thegastrointestinal tract. Dissolved arsenic in drinking water is well absorbed from the gastrointestinaltract. In comparison, as a result of tight binding, arsenic absorption from a mineral or soil matrix willbe decreased relative to absorption from food or water.