Assessing the Mixture Effects in In Vitro Bioassays of Chemicals Occurring in Small Agricultural Streams during Rain Events

Abstract

Rain events may impact the chemical pollution burden in rivers. Forty-four small streams in Germany were profiled during several rain events for the presence of 395 chemicals and five types of mixture effects in in vitro bioassays (cytotoxicity, activation of the estrogen, aryl hydrocarbon and peroxisome proliferator-activated receptors and oxidative stress response). While these streams were selected to cover a wide range of agricultural impacts, in addition to the expected pesticides, wastewater-derived chemicals and chemicals typical for street run-off were detected. The unexpectedly high estrogenic effects in many samples indicated impact by wastewater or overflow of combined sewer systems. The 128 water samples exhibited a high diversity of chemical and effect patterns, even for different rain events at the same site. The detected 290 chemicals explained only a small fraction (<8 %) of the measured effects. The experimental effects of designed mixtures of detected chemicals that were expected to dominate the mixture effects of detected chemicals were consistent with predictions for concentration addition by a factor of two for 94 % of the mixtures.Overall, the burden of chemicals and effects were much higher than previously detected in surface water during dry weather with the effects often exceeding effect-based trigger values. In-vitro bioassay test batteryEndocrine effects • ER Metabolism • AhR • PPARy Adaptive stress response: • Oxidative stress Chemical analysis Sampling triggered by rain events Mixture models

Exploring the Concepts of Concentration Addition and Independent Action Using a Linear Low‐Effect Mixture Model

“…Variability of controls can be reduced to a coefficient of variance of 2 to 10%, making it therefore possible to work at low effect levels and deduced effect concentrations for 10% of effect, EC10. These ECs are higher than concentrations occurring in water, but they come closer (Neale et al 2020). We can confidently assume that a concentration-response model that explains an effect at approximately the 10% effect level can be used to extrapolate to lower effects, certainly better than a model that focuses on giving a best estimate of EC50.…”

“…The measured cytotoxicity of the designed mixtures agreed within a factor of 10 with the prediction for CA (Figure 2A). This is a poorer agreement than for the specific effects in the same experiments (Neale et al 2020), where agreement was typically within a factor of 2; but this is because the cytotoxicity measurements were performed using imaging methods that have a larger variability than the quantification of the reporter gene product. In addition, the solvent dimethylsulfoxide, which was required to prepare such multicomponent mixtures, might have contributed to the cytotoxicity, in particular for AhR-CALUX.…”

“…We also investigated the significance of these considerations for mixtures of organic chemicals in water. Few studies have addressed the effects of realistic environmental mixtures, combining chemicals in concentration ratios as they occur in water (Junghans et al 2006; Neale et al 2020) or sediment (Altenburger et al 2004). Component‐based methods have been recommended to estimate the effect of complex mixtures of chemicals in surface water (Posthuma et al 2019).…”

“…In a first case study, we compared the predictions of CA and IA in over 200 designed mixtures of 2 to 17 chemicals that were mixed in concentration ratios as they had been detected in water samples collected from small rivers during rain events and tested for activation of reporter gene activity and cytotoxicity (Neale et al 2020). Because reporter gene activation is strictly CA, we used the cytotoxicity for this illustration.…”

“…Data Availability Statement-All toxic unit data of the first case study are available in Neale (2020) or from the corresponding author (beate.escher@ufz.de). The effect data and concentrations of the second case study are available in the Supplemental Data files of Massei (2018) and Kandie (2020).…”