Pesticides are potentially toxic to aquatic systems, even at low concentrations, depending on their individual ecotoxicological properties and mixture composition. To evaluate the possible ecological stress caused by pesticide load, a thorough assessment of the potential toxicity of pesticide mixtures is required. Here we report water discharge and quality data from an eastern Mediterranean micro-estuary (Alexander stream), targeting the temporal distribution of a pesticide mixture. Over 150 water samples were collected during two hydrological years, representing base-flow and flood conditions. On average, each water sample contained 34 and 45 different pesticides, with peak concentrations of 1.4 µg/L of Imidacloprid and 55 µg/L of Diuron during base-flow and flood events, respectively.
Pesticide mixtures were potentially toxic to benthic invertebrates and algae during flood events, surpassing the toxicity benchmark with medians of 110% and 155%, respectively. The herbicide Diuron and the insecticide Imidacloprid were the main pesticides responsible for the high potential toxicity during floods. The falling limb of the flood hydrograph was found to inflict the highest stress on the estuarine environment, due to elevated toxicity combined with prolonged residence time of the water. Examination of the potential chronic toxicity of single compounds showed continuous stress for plants, algae, amphibians, crustaceans, insects and fish from nine pesticides.
The data show that the Alexander micro-estuary ecosystem is under continuous chronic stress, with acute peaks in potential toxicity during flood events and the period that follows them. We propose that analyzing a small set of flood-tail samples is needed to evaluate small estuarine ecosystem risk during the rainy season, and recommend tighter control of Diuron application practices in the watershed to minimize the stress on the estuarine system.
Citation: Topaz, T., Egozi, R., Suari, Y., Ben-Ari, J., Sade, T., Chefetz, B., & Yahel, G. (2020). Environmental risk dynamics of pesticides toxicity in a Mediterranean micro-estuary. Environmental Pollution, 265, 114941. https://doi.org/10.1016/j.envpol.2020.114941