ASSESSING THE TOXICITY OF BETANAL+ ON GROWTH AND SENSITIVENESS OF FIVE FRESHWATER PLANKTONIC SPECIES

The widespread increase of pesticides application in crops frequently leads to the contamination of freshwater ecosystems. Betanal Expert+ is a post-emergent herbicide which retards the emergence of shoots, inhibits the growth of meristems and cell division, and limits the waxy cuticle formation. Phytoplankton (micro-algae) and zooplankton (micro-invertebrates) have long been used as suitable groups to assess the impact of environmental change, in part due to their position in the trophic food web. This study aims to determine the Betanal Expert+ thresholds which inhibit the growth of three freshwater green microalgae - Pseudokirchneriella subcapitata (Korshikov) Hindak, Chlorella vulgaris Beijerinck and Chlamydomonas pseudocostata Pascher & Jahoda -, as well as the acute toxicity effects on two freshwater cladoceran species - Daphnia magna Straus and Daphnia longispina O. F. Mueller. P. subcapitata showed to be the most sensitive alga and C. pseudocostata the most tolerant to this agrochemical (EC sub(50) 3.22 and 266 kg-L super(-1), correspondingly). The EC sub(50) value determined for C. vulgaris was 22.5 kg.L super(-1). Acute tests demonstrated that D. magna is more tolerant than D. longispina (EC sub(50) 4.45 and 2.73 mg.L super(-1), respectively) to the toxicant. The results of this work suggest that the application of this herbicide for weed control in agricultural practices must be done carefully, since any disturbance affects planktonic species with similar or higher sensitivity which may have severe repercussions on higher trophic levels.