Biochemical and toxicological effects of organic (herbicide Primextra(®) Gold TZ) and inorganic (copper) compounds on zooplankton and phytoplankton species.

In Europe, mainly in the Mediterranean region, an intensive usage of pesticides was recorded during the past 30 years. According to information from agricultural cooperatives of the Mondego valley (Figueira da Foz, Portugal), Primextra(®) Gold TZ is the most used herbicide in corn crop fields and one of the 20 best-selling herbicides in Portugal. Copper is mainly used in pesticide formulations. This study aims to determine the ecotoxicological and biochemical (namely fatty acid profiles) effects of the herbicide Primextra(®) Gold TZ and the metal copper on marine plankton. The organisms used in this study are three planktonic species: the marine diatom Thalassiosira weissflogii, the estuarine copepod Acartia tonsa and nauplii of the marine brine shrimp Artemia franciscana. Fatty acids (FAs) are one of the most important molecules transferred across the plant-animal interface in aquatic food webs and can be used as good indicators of stress. The conducted lab incubations show that T. weissflogii is the most sensitive species to the herbicide followed by A. tonsa (EC50=0.0078mg/L and EC50=0.925mg/L, respectively), whereas the copepod was the most sensitive species to the metal followed by T. weissflogii (EC50=0.234mg/L and EC50=0.383mg/L, respectively). A. franciscana was the most tolerant organism both to the herbicide and to the metal (EC50=20.35mg/L and EC50=18.93mg/L, respectively). Changes in the FA profiles of primary producer and primary consumers were observed, with the increase of saturated FA and decrease of unsaturated FA contents, especially of highly unsaturated FAs that can be obtained mainly from food and therefore are referred to as 'essential FA'. The study suggests that discharges of Primextra(®) Gold TZ or other pesticides mainly composed by copper may be a threat to plankton populations causing changes in the FA contents and thus in their nutritive value, with severe repercussions for higher trophic levels and thus the entire food web.