Cytotoxic effects of pesticides on microalgae determined by flow cytometry

Abstract

As much as ca. 99.7% of the applied load of pesticides is dispersed in the environment, not reaching the target pests. In this way, pesticides enter into aquatic ecosystems from agricultural runoff or leaching and, as a consequence, have become some of the most frequently ocurring organic pollutants in aquatic ecosystems. Most phytotoxicological research with herbicides has been conducted on target plants. The sensitivity of algae to many herbicides is very high, and a better understanding of their environmental effects is probably acquired by using test species representing non-target groups. Because of their short generation times, microalgae respond rapidly to environmental changes. Furthermore, microalgal tests are generally sensitive, rapid and low-cost effective. For these reasons, the use of microalgal toxicity tests is increasing, and today these tests are frequently required by authorities for notifications of chemicals and are also increasingly being used to manage chemical discharges. Cytotoxic effects of aquatic pollutants on microalgae are very heterogeneous, and they are influenced by the environmental conditions and the test species. Growth, photosynthesis, chlorophyll fluorescence and others parameters reflect the toxic effects of pollutants on microalgae; however, other relevant endpoints are less known because experimental difficulties, especially under in vivo conditions. Flow cytometry offers multiparametric analysis of cells on a cell-by-cell basis in near in vivo conditions. Applied in the study of the aquatic environments since the 80's, this technique has achieved extensive use for the study of microalgae and has been introduced as an alternative to more traditional techniques of analyzing cells in culture and from natural populations. Several parameters determined by flow cytometry, such as cell volume and granularity, chlorophyll a fluorescence, cell viability, cell proliferation, oxidative stress, membrane potential or intracellular calcium level, were employed to assess changes in the physiological status of different microalgae as a consequence of the toxic action of herbicides. The variety of results obtained in the present study reveals that flow cytometry is a useful tool in the toxicity tests with microalgae.