Abstract
Health risk assessments of exposures to harmful materials increasingly are required because of legal and economic pressures. An important part of the procedure is the mathematical model for the dose-effects relationship. If a linear no-threshold relationship is assumed, then the mean of fluctuating concentrations may be used for the calculation of health risk. But the widely used PEL and TLV® values assume a threshold relationship. For this and for nonlinear relationships the calculation with the use of the mean concentration is inaccurate, because higher concentrations produce disproportionately higher effects. An appropriate mathematical model based upon lognormal concentrations and probit effects is proposed. Rather than monitoring concentrations for unlikely high values, the method requires estimation of their geometric mean and geometric standard deviation. A health risk assessment then may be calculated simply and conveniently from the charts and tables provided. The method clarifies some issues and the specifics of utilizing and improving the required data. The model should be useful for assessing health risks from fluctuating concentrations of most toxic compounds.