Effects of Pesticides on Freshwater Diatoms

Abstract

The study of pesticide effects on algae, and diatoms in particular, was focused on photosynthesis and biomass growth disturbances. Few studies have been performed to investigate the effects of these toxic agents on intracellular structures of diatom cells. Nuclear alterations and cell wall abnormalities were reported for diatoms exposed to toxic compounds. Nevertheless, the cellular mechanisms implicated in the development of such alterations and abnormalities remain unclear. Sensitivity to pesticides is known to be quite different among different diatom species. Eutrophic and small species are recognized for their tolerance to pesticides exposure. More pronounced cell defenses against oxidative stress may explain this absence of sensitivity in species of smaller physical size. Notwithstanding, on the whole, explaining the rationale behind tolerance variations among species has been quite difficult, thus far. In this context, the understanding of intracellular toxicity in diatoms and the relation between these intracellular effects and the disturbance of species composition in communities represent a key target for further research. The original community species structure determines the response of a diatom community to toxic agent exposure. Diatom communities that have species capable of switching from autotrophic to heterotrophic modes, when photosynthesis is inhibited (e.g., after pesticide exposure), can continue to grow, even in the presence of high pesticide pollution. How diatoms respond to toxic stress, and the degree to which they respond, also depends on cell and community health, on ecological interactions with other organisms, and on general environmental conditions. The general structural parameters of diatom communities (biomass, global cell density) are less sensitive to pesticide effects than are the specific structural parameters of the unicellular organisms themselves (cell density by species, species composition). For benthic species, biofilm development and grazing on this matrix as a source of food for invertebrates and fishes may also modify the response of diatom communities. Environmental parameters (light exposure, nutrient concentrations, and hydraulic conditions) affect, and often interfere with, the response of diatoms to pesticides. Therefore, the complexity of aquatic ecosystems and the complexity of pesticide to easily detect the effects of such pollutants on diatoms. Clearly more research will be required to address this problem.

Temperature and Light Modulation of Herbicide Toxicity on Algal and Cyanobacterial Physiology

“…ROS accumulation ultimately induces cellular oxidative bursts that damage pigments and proteins, and the lipids of the photosynthetic apparatus (Gonzáles-Barreiro et al, 2004). Atrazine and temperature are therefore both environmental factors that affect algal and cyanobacterial photochemistry, and their interactive effects have been previously studied (Bérard et al, 1999;Debenest et al, 2010;Chalifour and Juneau, 2011;Larras et al, 2013). Since atrazine is mainly applied when water temperatures are still low (<20 • C) in the Northern hemisphere, its interaction with temperature is essential to take into account.…”

Impact of the herbicide metolachlor on river periphytic diatoms: Experimental comparison of descriptors at different biological organization levels

“…The appearance of diatom deformities is often presumed to result from Si limitation (Debenest et al, 2010). However, from this study, this hypothesis can be rejected for several reasons: (1) there was a clear dose effect in the channels and there was most Si left in one of the most contaminated channels (30b); (2) in the monospecific test, deformities were significantly more abundant in the contaminated cultures; and (3) Si limitation did not produce more abnormal forms than control conditions.…”

Test of Direct and Indirect Effects of Agrochemicals on the Survival of Fecal Indicator Bacteria

“…For instance, agrochemicals can alter the traits of an organism, such as behavior, immunity, physiology, or morphology, thereby affecting its interactions with other species. This effect has been seen in multicellular organisms (39-41, 43, 45) and microorganisms (15)(16)(17). Alternatively, agrochemicals may cause density-mediated, rather than trait-mediated, indirect effects via direct toxicity to a target species' food resources, parasites, competitors, or predators (18,21,22,36,41,(44)(45)(46)51).…”