Laserfiche WebLink
y Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br /> Two methods of dose-response analysis are widely used to estimate Cfects in humans at low <br />' exposure levels. The first method is mathematical modeling of the dose-response relationship. <br /> The mathematical modeling approach is often used to characterize the relationship between the <br /> dose of a carcinogenic chemical and the incidence of cancer. <br /> The second method of assessing the dose-response relationship is through the safety factor <br /> approach. This method is used to describe the relationship between the dose and the effects of <br /> ' noncarcinogenic chemicals. The induced effect is assumed to have a threshold, below which <br /> adverse health effects would not be seen. Exposure levels that do not result in adverse health <br /> effects in animals are extrapolated to human exposures using safety factors. The two methods <br /> ' of dose-response analysis are discussed in the following sections. <br /> 4.1 CARCINOGENIC RESPONSE <br /> ' Mathematical modeling may be separated into two different categori nonphysiological and <br /> physiological modeling. Nonphysiological modeling fits a preselected �;.irve to the experimental <br /> data. Physiological modeling attempts to describe the data in terms of the mechanism of action. <br /> Each model utilizes many assumptions that affect the manner in which the dose-response <br /> relationship is estimated. <br /> Currently, the U.S. and California Environmental Protection Agencies use the Linearized Multi- <br /> Stage (LMS) model. The LMS model is a nonphysiological mathei.l.-itical model which, in <br />' conjunction with experimental data, is used to estimate the Cancer Slapf Factor of a potentially <br /> carcinogenic chemical. The dose-response-relationship for carcinogens is assumed to be linear <br /> ' and without a threshold. This means that the model assumes there is some risk associated with <br /> any dose of the chemical, theoretically even one molecule. <br /> Potential health risks resulting from exposure to carcinogenic chemicals are defined in terms of <br /> probabilities. The probability distinguishes the likelihood of a carcuiogenic response in an <br /> individual exposed to a known or predicted dose of a particular chemical and is expressed in <br /> i <br /> 30-0136-11 4-2 <br /> i <br />