The legends presented below demonstrate the application of these tables and figures. All entries in these tables and figures represent studies that provide reliable, quantitative estimates of NOAELs, LOAELs, or Cancer Effect Levels (CELs). The LSE tables and figures should always be used in conjunction with the text. Use the LSE tables and figures for a quick review of the health effects and to locate data for a specific exposure scenario.

These levels cover health effects observed at increasing dose concentrations and durations, differences in response by species, MRLs to humans for noncancer end points, and EPA’s estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. Tables and figures are used to summarize health effects and illustrate graphically levels of exposure associated with those effects. Tables and Figures for Levels of Significant Exposure (LSE) Uncertainty factors used in developing a substance-specific MRL are provided in the footnotes of the levels of significant exposure (LSE) tables. The product is then divided into the inhalation concentration or oral dosage selected from the study. In deriving an MRL, these individual uncertainty factors are multiplied together. Additional uncertainty factors of 10 must be used both for human variability to protect sensitive subpopulations (people who are most susceptible to the health effects caused by the substance) and for interspecies variability (extrapolation from animals to humans). When a NOAEL is not available, a lowest-observed-adverse-effect level ( LOAEL) can be used to derive an MRL, and an uncertainty factor ( UF) of 10 must be employed. If this information and reliable quantitative data on the chosen end point are available, ATSDR derives an MRL using the most sensitive species (when information from multiple species is available) with the highest no-observed-adverse-effect level ( NOAEL) that does not exceed any adverse effect levels. ATSDR cannot make this judgement or derive an MRL unless information (quantitative or qualitative) is available for all potential systemic, neurological, and developmental effects. To derive an MRL, ATSDR generally selects the most sensitive end point which, in its best judgement, represents the most sensitive human health effect for a given exposure route and duration. MRLs are derived using a modified version of the risk assessment methodology that the Environmental Protection Agency (EPA) provides ( Barnes and Dourson 1988) to determine reference doses (RfDs) for lifetime exposure. MRL users should also understand the MRL derivation methodology. Other sections such as Chapter 3 Section 3.9, “Interactions with Other Substances,” and Section 3.10, “Populations that are Unusually Susceptible” provide important supplemental information. Chapter 2, “Relevance to Public Health,” contains basic information known about the substance. MRL users should be familiar with the toxicologic information on which the number is based. MRLs are based largely on toxicological studies in animals and on reports of human occupational exposure. MRLs should help physicians and public health officials determine the safety of a community living near a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. These MRLs are not meant to support regulatory action, but to acquaint health professionals with exposure levels at which adverse health effects are not expected to occur in humans. Where sufficient toxicologic information is available, ATSDR has derived MRLs for inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic). Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to public health are identified in the Chapter 3 Data Needs section. Minimal Risk Levels (MRLs) for noncancer end points (if derived) and the end points from which they were derived are indicated and discussed. ATSDR does not currently assess cancer potency or perform cancer risk assessments. The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using existing toxicokinetic, genotoxic, and carcinogenic data. In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.) are also considered in this chapter. Both are organized by duration (acute, intermediate, chronic).

Human data are presented first, then animal data. The chapter covers end points in the same order that they appear within the Discussion of Health Effects by Route of Exposure section, by route (inhalation, oral, and dermal) and within route by effect. What exposure conditions are likely to be of concern to humans, especially around hazardous waste sites?

Satisfactory guide