Abstract
The authors present a method to predict fish survival under exposure to fluctuating concentrations and repeated pulses of a chemical stressor. The method is based on toxicokinetic-toxicodynamic modeling using the general unified threshold model of survival (GUTS) and calibrated using raw data from standard fish acute toxicity tests. The model was validated by predicting fry survival in a fish early life stage test. Application of the model was demonstrated by using Forum for Co-ordination of Pesticide Fate Models and Their Use surface water (FOCUS-SW) exposure patterns as model input and predicting the survival of fish over 485 d. Exposure patterns were also multiplied by factors of five and 10 to achieve higher exposure concentrations for fish survival predictions. Furthermore, the authors quantified how far the exposure profiles were below the onset of mortality by finding the corresponding exposure multiplication factor for each scenario. The authors calculated organism recovery times as additional characteristic of toxicity as well as number of peaks, interval length between peaks, and mean duration as additional characteristics of the exposure pattern. The authors also calculated which of the exposure patterns had the smallest and largest inherent potential toxicity. Sensitivity of the model to parameter changes depends on the exposure pattern and differs between GUTS individual tolerance and GUTS stochastic death. Possible uses of the additional information gained from modeling to inform risk assessment are discussed. Environ. Toxicol. Chem. 2013;32:954–965. © 2013 SETAC
Highlights
Assessing the ecological risk of plant protection products (PPPs) requires the comparison of toxicity data for sensitive nontarget species with worst-case predicted exposure concentrations in the environment
Parameters converged to plausible best fit parameter values for both fish species and both the general unified threshold model of survival (GUTS)-stochastic death (SD) and the GUTS-individual tolerance (IT) models without the need for parameter constraints. These parameter values were used for the predictive simulations with the concentration profiles from FOCUS-SW scenarios
Profiles of the likelihood were calculated for each parameter to derive the confidence limits
Summary
Assessing the ecological risk of plant protection products (PPPs) requires the comparison of toxicity data for sensitive nontarget species with worst-case predicted exposure concentrations in the environment. Toxicity data used in these assessments usually are obtained from studies in which exposure concentrations are maintained for the duration of the experiments, usually lasting several days (for acute studies) to several weeks (for chronic studies). Under realistic environmental conditions, concentrations of PPPs in aquatic systems will fluctuate, and exposure profiles may vary substantially [1,2,3]. Risk assessments do not typically consider the nature of effects on nontarget species from fluctuating exposures that are likely to be encountered in the field; instead, peak or timeweighted average concentrations usually are used [4,5,6]. It remains unclear how to appropriately integrate these exposure profiles with the effect assessments to refine the risk assessments [3]
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