Effects of light and temperature fluctuations on the growth of Myriophyllum spicatum in toxicity tests—a model-based analysis

Abstract

Laboratory toxicity tests are a key component of the aquatic risk assessments of chemicals. Toxicity tests with Myriophyllum spicatum are conducted based on working procedures that provide detailed instructions on how to set up the experiment, e.g., which experimental design is necessary to get reproducible and thus comparable results. Approved working procedures are established by analyzing numerous toxicity tests to find a compromise between practical reasons (e.g., acceptable ranges of ambient conditions as they cannot be kept completely constant) and the ability for detecting growth alterations. However, the benefit of each step of a working procedure, e.g., the random repositioning of test beakers, cannot be exactly quantified, although this information might be useful to evaluate working procedures. In this paper, a growth model of M. spicatum was developed and used to assess the impact of temperature and light fluctuations within the standardized setup. It was analyzed how important it is to randomly reassign the location of each plant during laboratory tests to keep differences between the relative growth rates of individual plants low. Moreover, two examples are presented on how modeling can give insight into toxicity testing. Results showed that randomly repositioning of individual plants during an experiment can compensate for fluctuations of light and temperature. A method is presented on how models can be used to improve experimental designs and to quantify their benefits by predicting growth responses.

Scientific Opinion on the state of the art of Toxicokinetic/Toxicodynamic (TKTD) effect models for regulatory risk assessment of pesticides for aquatic organisms

“…(); Heine et al. (, , ). External factors affecting chemical uptake or growth are given in blue, internal chemical concentrations in orange and the different rate constants affecting biomass growth of the plants or algae in the respective models are given in green.…”

“…are more complex plants; hence, the growth model is more complex as compared to the Lemna model. Myriophyllum is rooted, hence, the growth model needs at least root, stem and shoot compartments, which are explicitly introduced (Heine et al., ) and modelled in Heine et al. (, ).…”

“…(, ). In the original growth model (Heine et al., ), photosynthesis takes place in the leaves and biomass is allocated to leaves, stems and roots in the fixed proportions 55:35:10%, which is an average based on literature data (Jiang et al., ). Uptake of chemicals can take place by leaves, stems and roots using the same cuticular permeability constant for all three tissues, but different surface to volume ratios.…”

A toxicokinetic and toxicodynamic modeling approach using Myriophyllum spicatum to predict effects caused by short‐term exposure to a sulfonylurea

“…To predict the impact of short‐term iofensulfuron exposures on M. spicatum , a toxicokinetic and toxicodynamic growth model was used. A detailed description of the growth and of the toxicokinetic model can be found in Heine et al . These publications contain all equations considered and a complete parameterization of the model.…”

“…The aim of the present study was to integrate toxicodynamics in an already published toxicokinetic growth model of Myriophyllum spicatum , to develop a model that is able to predict the effects of time‐variable chemical exposure. To show the applicability of the model, the effects of 2 short‐term exposure scenarios of a sulfonylurea compound that causes adverse effects on the growth of aquatic plants were predicted.…”