Deterministic endpoints

The risk index for any hazardous substance in Equation 1.1 or 1.2 (see Section 1.5.1) is calculated based on assumed exposure scenarios for hypothetical inadvertent intruders at near-surface waste disposal sites and a specified negligible risk or dose in the case of exempt waste or acceptable (barely tolerable) risk or dose in the case of low-hazard waste. Calculation of the risk index also requires consideration of the appropriate measure of risk (health-effect endpoint), especially for carcinogens, and the appropriate approaches to estimating the probability of a stochastic response per unit dose for carcinogens and the thresholds for deterministic responses for noncarcinogens. Given a calculated risk index for each hazardous substance in a particular waste, the waste then would be classified using Equation 1.3. 

The results in Table 7.8 indicate that the organ- and endpoint-specific risk indexes are about 0.7 to 0.8 in all cases, due mainly to intakes of lead. The maximum risk index for any organ or endpoint is about 0.8. Truncating this result using the INTEGER function, as indicated in Equation 6.5, gives a risk index for all deterministic hazardous chemicals in the waste of zero. This result means that the calculated dose in all organs and for all endpoints due to exposure to all deterministic substances that cause deterministic responses in the waste is less than the assumed acceptable dose of 10 times RfDs. Therefore, based only on consideration of substances that... 

There has been a large increase in recent years in the application of SSDs in ecotoxi-cology, as evidenced by the recent SETAC (Society of Environmental Toxicology and Chemistry) book by Posthuma et al. (2002). This approach is being or will shortly be applied in the European Union, Australia, United States, and Canada, with a general movement (where possible) toward the use of ECx in preference to the historical use of AFs and NOECs in deterministic PNEC calculations. The toxicity endpoint used will depend on the objective. For deriving a MAC-EQS, LC(EC)50 data are appropriate, while chronic NOECs (or preferably chronic ECx values, where available) are applicable for AA-EQSs. 

Selection of the appropriate metric for use in the risk assessment can have a significant impact on the outcome of an assessment. Regardless of the mathematical approach used, it is important that harmonized guidance exists for metric selection. Guidance should be based on a number of considerations, including data quality, data quantity, distribution type, duration of exposure and nature of the toxicology endpoint. Based on personal experience with numerous deterministic exposure assessments, it is clear that regulatory authorities differ with respect to input and output metric selections. 

A trend in the data is defined (46) as any frequency component whose period is longer than the sample record. Failure to remove these trends often produces large distortions in correlation functions (and spectra), especially at low frequencies. A least-squares detrending procedure (46) was used to remove linear trends in the data. This method differs from the endpoint technique 49, 50). The end-point technique was not used here because it is recommended for use on data in which a large deterministic com-... 

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