The basic algorithms presented in the last six slides are far from adequate for exposure calculation. For example, the last slide suggested that data on handler exposure for other chemicals can be used as surrogate, in that handler exposures tend to be proportional to the amount of chemical handled, rather than to the specific chemical handled. Yet the personal protective equipment (PPE) and clothing requirements for one product may be quite different from those for the surrogate product. Adjustment for such differences would require a knowledge of clothing penetration or of the mitigation efficacy of certain PPE (e.g., respirator, headgear, goggles).

Because people can be subject to the same or different long- and short-term adverse effects, the number of days they work in a season is a critical factor in calculating their intermediate and long-term exposures from handling a chemical. It is also difficult to determine what actually constitutes an average or a reasonable maximum default rate or value for some of the exposure-related parameters. To overcome some of the controversies over the use of these values, U.S. EPA (1997a) has provided a three-volume Exposure Factors Handbook as reference. Included in this handbook are literature reviews and some suggested percentiles, means, and medians for (age- or gender-specific): inhalation rates; soil ingestion rates and pica; patterns of occupational and population mobility; intake rates of various food items (including vegetables, fruits, fish, meat products, and grain products); body surface areas; intake of drinking water; intake of breast milk; and many more.