|
(W/MF161) Risk assessment and diagnostic of pollution: use of chlorophyll fluorescence as endpoint in revealing PICT in algal communities contaminated by PSII inhibitors. Bérard, Annette1, Dorigo, Ursula1, Seguin, Florence1, Leboulanger, Christophe1, 1 ABSTRACT- Single species toxicity tests and environmental chemistry are not sufficient to evaluate ecosystem health because they do not incorporate the complexity of assemblages of organisms interacting with each other and with their abiotic environment. To conduct aquatic ecological risk assessment of pesticides we need ecotoxicological tools which integrate this complexity. More precisely, tests which reflect both functional and structural aspects of ecosystems. The concept of Pollution-Induced Community Tolerance (PICT), has been developed by Blank et al. (1988) as an ecotoxicological tool to determine the impact of a chemical at the community level. This method can be used to retrospectively detect the impact of toxicants in polluted natural ecosystems or for predictive purposes, using artificial systems. We have developed a test that measures in vivo chlorophyll a fluorescence variables to determine the apparent sensitivity of freshwater periphytic and phytoplanktonic algae to photosystem II inhibitors. Natural periphytic and phytoplanktonic communities from microcosms, mesocosms, rivers and lakes were collected, and the effects of short-term exposures to two PSII herbicides (atrazine and irgarol) on the fluorescence parameters were measured with a pulse-amplitude modulated fluorometer (periphyton) or a Turner fluorimeter (phytoplankton). The effective concentrations for each herbicide and community were calculated from fluorescence yield indices. Periphyton and phytoplankton sensitivities were compared in different contaminations and systems. Communities sampled in contaminated stations or micro-mesocosms were less sensitive than communities sampled in reference stations and control systems. The fluorescence-based method appears to give very reliable estimation of PICT for each pesticide and community we tested. This method could be used in monitoring programs of ecotoxicology and risk assessment, to detect changes in natural periphyton or phytoplankton populations sensitivity, following photosystem II herbicide contaminations in experimental systems, rivers or lakes. Key words: fluorescence, community tolerance, herbicides, photosynthesis |
