Valutazione del potenziale tossicologico di un erbicida attraverso saggi multispecie

Silvia Castiglioni*°, Elisa Di Gioia*, Corrado L. Galli°, Maria Rosa Lovati*° Università degli Studi di Milano, *Lab. Tossicologia Ambientale, via S. Francesco 13-26900 Lodi, °Dip. di Scienze Farmacologiche, via Balzaretti 9-20133 Milano

Pendimethalin (N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine), belonging to dinitroaniline group, is an herbicide classified as marine pollutant. Different symptoms such as SNC depression, dyspnoea, diuresis increase, convulsions and eyes irritation were described in humans exposed to high levels of pendimethalin. The risk assessment, following pesticides exposition, is at present addressed to prevent the potential damages both in humans and in ecosystems. In fact, the fate of a chemical in an entire ecosystem is a complex matter, involving movements in soils, surface waters and air, and transfer along food chain. From this, the knowledge of the movements of herbicides from their application site (crop fields) to surface watercourses and their sediments became an helpful tool to predict chemical leaking, through its transfer in interstitial water and soil particles, to deeper groundwater systems. Since pendimethalin is one of the most frequently used herbicides (rice, mais, wheat, e.g.) in the agricultural practice in the Po Valley, aim of the study was to evaluate the potential toxicity of the parent compound and its metabolite/s in water and soil samples, coming from treated crop fields, by ecotoxicological assays. These latter use a biological system as target for the identification and quantization of the environmental pollution damage. Moreover, these tests represent a powerful method that quickly supplies information, on a living being, of the interactive effects (potentiation of toxicity) of pollutants present in the environment. The organisms employed in the present research belong to the different trophic levels: producers (the unicellular green alga “Pseudokirchneriella subcapitata" and seeds of “Lepidium sativum", “Cucumis sativus" and “Sorghum saccharatum"), consumers (the crustaceans Daphnia magna and Heterocypris incongruens) and decomposers (the bioluminescent bacterium Vibrio fischeri). It is worthy to note that, although the ecotoxicological characterization of surface watercourses is requested by the Italian D.Lgs. 152/06, the Daphnia magna crustacean assay, the only test indicated by the law, seems not to be so sensitive to the environmental pollutants. Sixteen cement settling tanks (1 m2) were filled with 10 cm of gravel, 10 cm of non-cultivated soil and 10 cm of tap water in succession so as to mime watercourses in a natural situation. The following experimental plan was settled: 10 samples (surface water, ground water and sediment) were collected at different times: treatment day, 7, 15, 30, 45, 60, 90, 120, 150, 180 days from the beginning (t0). Two different pendimethalin formulation, one solvated with xylene and one micro-encapsulated, in 3 different concentrations 5-10-20 L/ha and 2 test tanks without herbicide, were used. Among the three kinds of examined matrices, the sediment was the compartment where the highest toxicity was detected, whereas no toxic effects were observed in the tester organisms when they were exposed to surface water. Between the two formulations, the micro-encapsulated was the most toxic product for the sediment fraction, whereas the solvated compound showed more toxicity for the ground water fraction. It was not possible to draw a dose-response relationship, since the increase in pendimethalin dosage did not determine the occurrence or the enhancement of the toxic effect. Among the bioassay used in the study, the bacterium Vibrio fischeri represented the most sensitive organism for the toxicity evaluation of the sediment.