PRINCIPLES OF TOXICOLOGY - Biology East Borneo

490 EXAMPLE OF RISK ASSESSMENT APPLICATIONSTABLE 19.7 Comparison of Arsenic Concentrations in Surface Soil to Urinary Arsenic Concentrationsin Children 0–6 Years of AgeReference and SiteNumber of ChildrenMean Concentration ofArsenic in Surface Soil(mg/kg)Mean Urinary ArsenicConcentration (µg/L) aBinder et al. (1987)Mill Creek, MT 10 648 66.1Anaconda, MT 92 127 14.4Opportunity, MT 25 113 10.6Livingston, MT 105 44 10.6Kalman et al. (1990)Ruston, WA 108 353 50.6Tacoma/Bellingham, WA 87 7–57 11.7Fort Valley, GA 15 14–140 < 10a Binder et al. (1987) based on total urinary [As]; Kalman et al. (1990), based on speciated urinary [As].sites, the USEPA encourages the inclusion of site-specific human exposure studies to strengthen theoverall conclusions of the risk assessment. For arsenic, there have been a number of studiesrelating human exposure to arsenic (measured by excretion of arsenic in the urine) to concentrationsof arsenic in soil.As discussed above, children 6 years of age or younger are generally considered the age group atmost risk of exposure to chemicals in soil because of their higher assumed soil ingestion rates. If it isassumed that a 15-kg child ingests 200 mg of soil per day that contains 90 mg/kg of arsenic and that80 percent of the arsenic in soil is absorbed, a child’s intake of arsenic is 14 µg/day. If it is furtherassumed that the average daily urinary for a 3-year-old child is 355 mL, the urinary arsenic concentrationfor a young child would be 41 µg/L.Studies that have examined the relationship between surface soil arsenic concentration and urinaryarsenic concentration in this age group are summarized in Table 19.7. Note that the 41 µg/L urinaryarsenic concentration calculated for a young child is well above mean urinary arsenic concentrationscalculated for children exposed to similar arsenic concentrations in soil in the Binder et al. (1987) andHewitt et al. (1995) studies. This comparison suggests that exposure factors used in calculating soilarsenic exposure may substantially overestimate actual exposure. These factors may include theassumption of high bioavailability of arsenic in soil (80 percent) as well as upper end estimates of achild’s daily soil ingestion.19.6 REEVALUATION OF THE CARCINOGENIC RISKS OF INHALED ANTIMONYTRIOXIDEWe examine the animal carcinogenicity data for antimony trioxide and possible mechanisms to explainthe carcinogenic action of antimony trioxide as an example of the hazard identification step of thehuman health risk assessment process. The hazard identification step evaluates whether a chemicalcauses a particular toxic effect in humans (i.e., cancer), the strength of human, animal, or other evidencefor making this determination, and the overall quality of the toxicological data for predicting humantoxicity. The hazard identification step also considers the possible mechanism of toxicity to humansand the relevance of animal data in predicting human toxicity.The case of antimony trioxide also emphasizes the need for inclusion of up-to-date toxicologicalinformation in risk assessment. The National Research Council emphasized the iterative nature of riskassessment and encouraged inclusion of new, in-depth, toxicological data and the investigation of toxic