A stressor is any physical, chemical, or biological agent or condition that can cause adverse effects to organisms or ecosystems. In mCDR projects, examples include nickel, alkalinity, pH changes, and turbidity. The stressor you select determines which SSD and data are used for the assessment.
Compartment is the environment where the stressor is released or measured. FEMM uses: sediment, porewater, discharge pipe, and water column. Compartment can affect data filtering and guidance for your assessment.
Regulatory context describes the setting that applies to your project (e.g. Temperate vs Tropical, Freshwater vs Marine). Different regimes may use different assessment factors, risk thresholds, and reporting requirements. Select the context that matches your project location and permit needs.
PEC (Predicted Environmental Concentration) is the concentration of a stressor that is predicted to occur in the environment, often calculated using fate and transport models. In risk assessment, RQ = PEC / PNEC. In FEMM MVP, users provide their own PEC value and unit; the system does not calculate PEC.
MEC (Measured Environmental Concentration) is the actual measured concentration of a stressor in the environment, e.g. from monitoring data. It is used in post-project assessments. FEMM MVP focuses on PEC; MEC may be supported in a future version.
A Species Sensitivity Distribution (SSD) is the distribution of species' sensitivities to a stressor (e.g. EC50 values from multiple species). The SSD is fitted to derive the HC5 (5th percentile). It is the core of the FEMM risk assessment approach.
ECx (Effect Concentration at x%) is the concentration of a stressor that causes a specified percentage of the maximum effect in a test organism (e.g. EC50 = 50% effect). ECx values from multiple species are the building blocks of the SSD. Lower ECx = more sensitive species.
A Dose-Response Curve (DRC) describes the relationship between dose (or concentration) and the magnitude of effect in an organism. ECx values are derived from DRCs; multiple ECx values build the SSD. DRC fitting from user data is not in MVP scope.
HC5 (Hazard Concentration for 5% of species) is the concentration at which 5% of species would be affected. It is derived from the Species Sensitivity Distribution (SSD) as the 5th percentile and is a key output of SSD fitting. PNEC = HC5 / Assessment Factor.
The Assessment Factor (AF), or uncertainty factor, is a safety factor applied to HC5 to account for data and extrapolation uncertainty. PNEC = HC5 / Assessment Factor. Typical values range from 1 to 10 depending on data quality and regulatory regime. Exact AF formulas for FEMM are to be defined with the science team.
PNEC (Predicted No Effect Concentration) is the concentration below which no adverse effects are expected. It is calculated as PNEC = HC5 / Assessment Factor. The PNEC is used as the 'safe' threshold in risk assessment; RQ = PEC / PNEC.
The Risk Quotient (RQ) is calculated as RQ = PEC / PNEC (or MEC / PNEC when using measured concentrations). RQ < 1 indicates low risk; RQ > 1 indicates potential risk and may require further assessment.
FEMM assigns risk classification by comparing PEC to T5 = HC5/AF (PNEC) and T10 = HC10/AF (same assessment factor). For one stressor: low if PEC ≤ T5, moderate if T5 < PEC ≤ T10, high if PEC > T10. RQ = PEC/PNEC is still reported and equals PEC/T5. For mixtures, low if sum(PEC/T5) ≤ 1, moderate if that sum exceeds 1 but sum(PEC/T10) ≤ 1, high if sum(PEC/T10) > 1. Certainty describes confidence in the classification, using PNEC confidence intervals for low-risk cases.
FEMM resamples your SSD data many times (bootstrap), refits each time, and builds a distribution of HC5 (then PNEC = HC5 ÷ assessment factor). From that distribution we take equal-tailed intervals: for example the 95% interval uses the 2.5th and 97.5th percentiles—not “5% and 10%.” See the diagram below. For low-risk classifications, certainty compares PEC to lower bounds on PNEC. High: PEC is below the 95% lower bound. Medium: PEC is between the 95% and 90% lower bounds. Low: PEC is at or above the 90% lower bound. For medium/high-risk classifications, certainty compares PEC to upper bounds and PNEC itself. High: PEC is above the 95% upper bound. Medium: PEC is above the 90% upper bound and at or below the 95% upper bound. Low: PEC is above PNEC and at or below the 90% upper bound. If either bound is missing, the level is Unknown.