Parabens are recognized as emerging contaminants. Used in the pharmaceutical and cosmetic industries, they present significant ecological risks to aquatic ecosystems. This study evaluated the effects of two parabens—methyl 4-hydroxybenzoate (methylparaben) and propyl 4-hydroxybenzoate (propylparaben)—both individually and as a mixture on daphnids. Through a series of controlled exposure experiments, phenotypic endpoints, including mortality, feeding behaviour, and enzymatic activity, were measured. The results demonstrate that propyl paraben and the mixture of propyl and methyl paraben exhibit greater toxic potential compared to methyl paraben alone. We observed a dose-dependent impact on key enzymes, indicating significant metabolic disruption. These findings underscore the necessity of utilizing model systems to investigate the complex interactions and cumulative impacts of pollutant mixtures in aquatic environments. Furthermore, this study provides critical insights regarding the underlying toxicity mechanisms of parabens, highlighting the need for comprehensive water quality monitoring and risk assessment frameworks to address the challenges posed by emerging contaminants.

Humanity faces the great challenges arising from pollution and climate change which evidently lead to the irreversible effects observed on the planet. It is now more important than ever to monitor and safeguard the ecosystem as it has been highlighted by governments and scientists. Conventional approaches for water pollution rely on the detection of chemicals in the environment. However, these descriptive observations when compared against water quality standards used as metrics for pollution are unable to predict pollution early or capture the extent of its impact. This weakness is reflected in the legislation and the thresholds for emerging pollutants such as pharmaceuticals and nanomaterials. To bridge the gap and to understand the underlying mechanisms for toxicity, research in the field of molecular ecotoxicology shifts more and more towards the integration of model systems, in silico approaches and molecular information as endpoints. Focusing on the freshwater ecosystem, daphnids are key species employed in risk assessment which are characterised as highly responsive to pollutants and physical stressors. The translation of molecular information describing the physiology of these organisms provides novel and sensitive metrics for pollution assessment.

Pollution is monitored in the ecosystem with methods that aim to capture the presence of pollutants. However, risk assessment is more oriented to develop sensitive metrics that rely on Novel Approach Methodologies (NAMs) which can support existing methods and offer mechanistic insight to the action of pollutants. Feeding is a phenotypic endpoint assessed in many organisms to describe changes in their physiology. For daphnids, feeding is usually quantified with assays employing large volumes and long incubation periods or even cumbersome techniques. In this paper we present a more robust and a faster method to assess feeding with simple fluorescence measurements based on the consumption of algae. The optimized protocol has been tested in a range of pollutants and feeding has proved to be a sensitive indicator for non-lethal exposures.

Daphnids, commonly known as water fleas, are freshwater planktonic microcrustacean species used as model organisms in ecotoxicology, particularly in regulatory frameworks that adhere to OECD and ISO standards. Mortality is the most common endpoint in toxicity testing; however, more sensitive indicators are required to assess sublethal acute effects of pollutants. The use of feeding impairment as a toxicity phenotypic endpoint in daphnids is considered a cost-effective approach that aligns with the 3Rs principle (Replace, Reduce, Refine) and is more physiologically and environmentally relevant. Current feeding methods are inefficient due to the large test volumes and extended incubation periods required. In this paper, we present a miniaturised protocol to assess feeding behaviour following exposure to chemicals in daphnids. The method is based on the consumption of algae, which is measured with chlorophyll fluorescence. The optimised protocol is more robust and rapid, and results can be obtained in 30 min and in a 96-well plate. Responses in feeding rate were investigated using this miniaturised protocol following exposure to a range of prevalent pollutants, which include two metals and, as a more realistic sample, a leachate from smoked cigarette filters. All three pollutants were tested at sublethal concentrations. This method provides an efficient approach to assess the toxicity of chemicals and water quality.