NOAEL and LOAEL stand for which concepts?

• A. No Observed Adverse Effect Level and Highest Observed Adverse Effect Level
• B. No Observed Adverse Effect Level and Lowest Observed Adverse Effect Level
• C. Not Observed Adverse Effect Level and Lowest Observed Adverse Effect Level
• D. Nominal Observed Adverse Effect Level and Low Observed Adverse Effect Level

Answer: (B)

No Observed Adverse Effect Level and Lowest Observed Adverse Effect Level. In dose–response testing, the highest exposure at which no adverse health effects are observed is the NOAEL, while the lowest exposure that does produce adverse effects is the LOAEL. These terms come from studies that use multiple dose groups to detect potential harm, helping establish safe exposure levels after applying uncertainty factors. If adverse effects are not seen at any tested dose, a LOAEL may not be defined and the NOAEL can be interpreted as the highest dose tested with no observed harm.