Padronização do teste de toxicidade com lentilhas d’água (Lemna minor) em solução hidropônica e sua aplicação na avaliação de um córrego urbano.

Abstract

Ecotoxicological tests require, for validation, both the use of a reference substance as a positive and an inert substance as a negative control. Standardized substances are those that have previously completed studies on their toxicity and reactions to a given test organism. The present work was subdivided into two studies: the first aiming to standardize the use of the commercial hydroponic solution as a culture medium for tests with Lemna minor and later the solution was applied as a control group in the evaluation of an urban stream. The duckweeds were repeatedly exposed to the hydroponic solution, along with four dilutions of NaCl, and water from five different collection points of the Barnabé Stream, located in Indaiatuba, SP. The exposure of about 12 fronds per repetition occurred over a period of seven days in an incubator, with controlled temperature and a photoperiod of 12 hours of light and 12 hours of darkness. The evaluated parameters were the calculation of the growth rate of the number of fronds and the leaf area. After statistical analysis, it was obtained as a result that the growth in hydroponic solution was much higher than that of sodium chloride, demonstrating that the solution presents itself as a viable and suitable culture medium for studies with L. minor, as well as, the parameters of number of fronds and leaf area showed sensitivity similar to the solution. After application as a control in the stream toxicity test, it could be considered that the stream water showed signs of toxicity to the macrophyte, seen both in the mean values and in the presence of the phenomenon of chlorosis in the fronds. Statistically, one collection point was not significantly different from the other, but all had low growth rates compared to the control group of the solution. In addition, for the collection points, the leaf area parameter was the most sensitive compared to the number of fronds, showing lower values.