GUTS-RED-models: GUTS-RED models

In cvasi: Calibration, Validation, and Simulation of TKTD Models

GUTS-RED models

Description

Reduced General Unified Threshold models of Survival (GUTS) with stochastic death (SD) and individual tolerance (IT)

Details

The TKTD models GUTS-RED-SD and GUTS-RED-IT were described by EFSA (2018). GUTS-RED models assume a one-compartment model which directly links external concentration to the scaled damage. The scaled damage is given in units of concentration, equal to the units of measurement in the external medium, e.g. ug/L. The damage dynamics is connected to an individual hazard state variable, resulting in simulated mortality when an internal damage threshold is exceeded. The death mechanisms stochastic death (SD) and individual threshold (IT) are extreme cases of the GUTS theory.

For SD models, the threshold parameter for lethal effects is fixed and identical for all individuals of a group, meaning that the variance of the threshold values is zero. Hence, the killing rate relates the probability of a mortality event in proportion to the scaled damage. For IT models, the thresholds for effects are distributed among individuals of a group. Mortality of an individual follows immediately once the individual's tolerance is exceeded. Meaning in model terms that the killing rate is set to infinity (EFSA 2018).

State variables

The following list describes the default names and standard units of GUTS-RED state variables:

• D, scaled damage (conc)

• H, cumulative hazard (-)

The state variables are initialized with zero by default.

SD model parameters

• kd, dominant rate constant (time^-1)

• hb, background hazard rate (time^-1)

• z, threshold for effects (conc)

• kk, killing rate constant (time^-1)

IT model parameters

• kd, dominant rate constant (time^-1)

• hb, background hazard rate (time^-1)

• alpha, median of thresholds (conc)

• beta, shape parameter (-)

Effects

The effect endpoint L (lethality) is available for GUTS-RED models. A value of zero (0.0) denotes no effect on organism survival. A value of one (1.0) denotes a lethality rate of 100%, i.e. no survivors.

The survival probability S is available in the return value of simulate().

References

EFSA PPR Panel (EFSA Panel on Plant Protection Products and their Residues), Ockleford C, Adriaanse P, Berny P, et al., 2018: Scientific Opinion on the state of the art of Toxicokinetic/Toxicodynamic (TKTD) effect models for regulatory risk assessment of pesticides for aquatic organisms. EFSA Journal 2018; 16(8):5377, 188 pp. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.2903/j.efsa.2018.5377")}

See Also

Other GUTS-RED models: GUTS_RED_IT(), GUTS_RED_SD()

Other scenarios: Algae-models, DEB-models, Lemna-models, Macrophyte-models, Myriophyllum-models, Scenarios, Transferable

cvasi documentation built on Sept. 23, 2024, 9:08 a.m.