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© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. This study investigates the impact of humic acid (HA) on the toxicity of selected herbicides and their binary mixtures to aquatic plants. The focus was on two auxin simulators (2,4-D and dicamba) and two photosynthetic inhibitors (atrazine and isoproturon). The results suggested that the addition of HA to the standard synthetic medium does not affect Lemna minor growth nor the toxicity of atrazine, but increases the toxicity of 2,4-D and the binary mixture of atrazine and 2,4-D. The addition of HA to the standard synthetic medium reversibly decreased the growth (biomass) of Myriophyllum aquaticum and enhanced the toxicity of individually tested herbicides (isoproturon and dicamba) as well as their binary mixture. The results showed delayed toxic effects of auxin simulators, especially 2,4-D in the Lemna test. The recovery after the exposure to individual photosystem II inhibitors (atrazine and isoproturon) is fast in both plant species, regardless of the presence of HA. In the case of selected mixtures (atrazine + 2,4-D and isoproturon + dicamba), recovery of both plant species was noted, while the efficiency depended on the herbicide concentration in the mixture rather than the presence or absence of HA.

© 2019, The Author(s). Background: Whole sediment contact tests provide realistic exposure scenarios, but the inherent properties of sediments may play a significant role in organism’s response and interfere with result interpretation. Recently, a sediment contact test with a rooted aquatic macrophyte Myriophyllum aquaticum has been standardized. The present study aims to distinguish between effects of basic sediment properties and sediment-bound pollutants on M. aquaticum growth and evaluate the method as a tool in sediment quality assessment. Tests with artificial sediments with different organic matter, sand and clay content, as well as freshwater sediments with different levels of contamination were conducted. Results: Results were based on comparison to the standard artificial control sediment. Organic matter content and grain size distribution in different variants of artificial sediments significantly affected M. aquaticum growth. Growth was impaired in formulations with low (1%) and high (10%) organic matter content, while better growth of plants compared to control was recorded in artificial samples with higher fine particles content. Because of the presence of unmeasured pollutants in freshwater sediments and inherent sediment properties, results of the M. aquaticum sediment contact tests were not always in accordance with the results of chemical analysis. Whorl, shoot and root parameters had different variability and showed a particular growth pattern in natural sediments. If the threshold of 20% for sediment toxicity is applied, then about 60% of tested natural sediments may be considered as toxic. As sediment structure may influence plant growth, this interpretation may be false as the physico–chemical properties of the control sediment used for comparison are considerably different from the properties of natural sediments. Conclusions: Since inherent properties showed a significant effect on plant growth, the use of suitable controls more similar to tested natural sediments is advisable. To avoid over-, but also under-estimations, the use of the strict toxicity threshold of 20% or even higher inhibition for this test can be recommended, provided the statistical power of the test is high. The results of this study might contribute to the ongoing process of including effect-based methods in water quality monitoring under the Water Framework Directive.

One active ingredient can be a component of different types of formulations of pesticides, while the toxicity of its formulations may vary depending on various constituents used in the mixture. The present study focuses on evaluating the effects of the active ingredient clomazone and its formulations (Rampa® EC and GAT Cenit 36 CS, both containing 360 g a.i./l of clomazone) on non-target aquatic macrophytes. The two formulation types differ in their active ingredient release and presumed environmental impact. In order to cover different ecological traits, two species of aquatic macrophytes – the floating monocot Lemna minor and the rooted dicot Myriophyllum aquaticum, were used as test models. The results of this study revealed differences in the sensitivity of tested plants to clomazone. Based on the most sensitive parameters, M. aquaticum proved to be more sensitive than L. minor to the technical ingredient and both formulations. The species sensitivity distribution (SSD) approach that was tried out in an attempt to create a higher tier step of risk assessment of clomazone for primary producers indicates that tests on rooted macrophytes can add value in risk assessment of plant protection products. The capsule formulation of clomazone was less toxic than the emulsion for L. minor, but more toxic for M. aquaticum. The most toxic for L. minor was the emulsifiable concentrate formulation Rampa® EC, followed by technical clomazone (EC50 33.3 and 54.0 mg a.i./l, respectively), while the aqueous capsule suspension formulation GAT Cenit 36 CS did not cause adverse effects. On the other hand, the most toxic for M. aquaticum was the formulation GAT Cenit 36 CS, followed by technical clomazone and the formulation Rampa® EC, demonstrating a greater effect of the capsule formulation. © 2021 Elsevier LtdAquatic macrophytes respond differently to different clomazone formulations, raising questions about the toxicity of conventional and newer formulations. © 2021 Elsevier Ltd