NOAEC

For systemic effects observed in inhalation smdies, the determining factor for effects to occur at the systemic target is generally the total dose rather than the concentration of the chemical in the air. In such cases, a tolerable intake (expressed as mg/kg body weight per day, or mg/m depending on the standard to be derived, i.e., a tolerable intake in its strict meaning, or a tolerable concentration) is estabhshed from the NOAEC, or LOAEC, derived in the inhalation smdy and adjusted for continuous exposure. 

In practice, this means that no adjustment for difference in body size is needed for a NOAEC obtained for systemic effects in an inhalation toxicity study (van Genderen 1988, Feron et al. 1990, Vermeire et al. 1999, KEMI 2003). For example, a NOAEC of 50 mg/m observed for laboratory animals is also the equivalent human NOAEC (note that so far species-specific sensitivity has not been taken into account). 

The authors concluded that neither effect addition nor potentiating interactions occurred, providing the exposure concentrations of the aldehydes are at their NOAECs. They also stated that the type of combined action or interaction found at clearly toxic effect levels was not very helpful in predicting what would happen at levels that are not toxic. 

Because of the first of these uncertainties (the extrapolation across species), assessments of risks to human health apply an uncertainty or safety factor of 100 to the experimentally derived no observed adverse effect concentration (NOAEC), in other words the NOAEC is divided by 100 to derive a no-effect level for human toxicity. This factor has been used since 1961, when it was chosen on an essentially arbitrary basis (RCEP, 2003, p22). In the assessment of risks to the environment, application factors of 10, 50, 100 or 1000 are applied to the results of tests carried out on specific species,2 depending on the species used and whether the tests were long term or short term. Evidence to the Royal Commission on Environmental Pollution (RCEP) for their report Chemicals in products indicated that these are merely extrapolation factors — they express the statistical variability of test results but do not effectively take into account inter-species variability, the vulnerability of threatened species, lifetime exposures or the complexity of biological systems... 

NOAEC/L No-observed-adverse-effect concentration/level. The highest level of exposure to a chemical in a test that does not cause statistically significant differences from the controls in any measured negative response. 

Often other terminology is used to describe the concentrations that have a minimal or nonexistent effect. Those that are currently common are NOEC, NOEL, NOAEC, NOAEL, LOEC, LOEL, MTC, and MATC. 

NOAEC — No observed adverse effects concentration determined by statistical hypothesis testing methods. The effect is usually chosen for its impact upon the species tested. 

Determine the no-adverse effect concentration/no-adverse effect levels (NOAECs/NOAELs) for the endpoint(s) of concern as established in Step 4. The most appropriate NOAEC/NOAEL is used to determine the microbiological ADI. NOAEC refers to no-observable adverse effect concentration and NOAEL to a no-observable adverse effect level. 

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