Introducing the No-Significant-Effect Concentration.

Area of Science:

• Environmental toxicology
• Ecotoxicology
• Risk assessment

Background:

• The no-effect concentration (NEC) is standard for deriving safe environmental contaminant levels but requires threshold responses in toxicity data.
• When concentration-response (C-R) data do not exhibit thresholds, NEC is unsuitable for risk assessment.
• Existing metrics like the no-observed-effect concentration (NOEC) have limitations, including dependence on experimental design.

Purpose of the Study:

• Introduce and validate the no-significant-effect concentration (NSEC) as an alternative toxicity metric.
• Provide statistical methods for estimating NSEC from C-R data lacking thresholds.
• Improve the derivation of safe environmental concentrations for contaminants.

Main Methods:

• Utilized a flexible, three-parameter sigmoidal function to model non-threshold C-R relationships.
• Developed and detailed both Bayesian and frequentist statistical approaches for NSEC estimation and inference.
• Compared NSEC to traditional metrics like NOEC, highlighting improvements in precision and reduced experimental design dependence.

Main Results:

• The NSEC provides a robust toxicity estimate for C-R data exhibiting monotonically decreasing responses without clear thresholds.
• Both Bayesian and frequentist methods offer reliable estimation and inference for NSEC.
• NSEC is a significant improvement over NOEC, offering more precise toxicity estimates independent of treatment concentration placement.

Conclusions:

• NSEC is a superior metric for environmental risk assessment when C-R data lack thresholds.
• The proposed statistical methods enable accurate NSEC determination.
• Adoption of NSEC will enhance the reliability of ecological risk assessments and the derivation of environmental quality standards.