Growth rate of Pseudokirchneriella subcapitata exposed to herbicides found in surface waters in the Alqueva reservoir (Portugal): a bottom-up approach using binary mixtures

Abstract

Previous work showed the existence of ecotoxicity of water samples from the Alqueva reservoir due to the presence of the herbicides atrazine, simazine, terbuthylazine and metolachlor. In the present study we examine the effects of these herbicides singly and as binary mixtures on the growth rate of the microalgae Pseudokirchneriella subcapitata. Usually, the toxicity of mixtures is evaluated in relation to the reference models CA (concentration addiction) and IA (independent action). In this study CA model was selected to evaluate the joint effects of s-triazine herbicides on the growth of algae due to their similar mode of action. Moreover, IA reference model was chosen to evaluate the joint toxicity of the chloroacetanilide metolachlor and the s-triazine herbicides due to their different mode of action. In this study dose ratio was the common deviation obtained on both reference models. In the binary mixtures between atrazine/simazine and atrazine/terbuthylazine the increase of the mixtures toxicity (synergism) was mainly due to atrazine. Also, in the binary mixture between atrazine and metolachlor, atrazine was responsible for the increase (synergism) of the mixture toxicity. In the cases of the binary mixtures between simazine/metolachlor and terbuthylazine/metolachlor, the increase of the mixtures toxicity (synergism) was detected when metolachlor was the herbicide dominant, and antagonism was detected when simazine and terbuthylazine were dominant in both mixtures. This study represents an important step to understand the interactions among herbicides detected previously in the waters of the Alqueva reservoir.

Photodegradation of Atrazine on TiO<sub>2</sub>―Products Toxicity Assessment

“…The test species of green alga, Raphidocelis subcapitata, is considered a sensitive and environmentally relevant model. The results observed in the present study for the non-irradiated atrazine samples are comparable with the results of Van der Heever et al [24] who reported IC 50 359 mg/l, even though lower IC 50 values for the same species were reported by Weiner et al [25] and Pérez et al [26] (48.77 µg/l and 196 µg/l, resp.) Experiments with fish RTgill-W1 cells did not show any toxic effects in both non-irradiated and irradiated atrazine samples.…”

Triazine Herbicides in the Environment

“…The results observed in the study for the non-irradiated atrazine samples are comparable with the results of Van der Heever et al [53] who reported IC 50 385 μg/l, even though lower IC 50 values for the same species were reported by Weiner et al [54] and Pérez et al [55] (48.77 μg/l and 196 μg/l, resp. )…”

Ecotoxicity and genotoxicity of a binary combination of triclosan and carbendazim to Daphnia magna

“…In the post-exposure period, five blanks with only algae and no daphnids were also prepared and maintained in the same conditions as the other beakers with daphnids, as previously describe for the exposure period. Feeding rates (cells/mL/ individual/hour) were determined in accordance with the method described by Allen et al (1995); algal concentration was measured using a colorimetric method at 440 nm for both exposure and post-exposure periods (Pérez et al, 2011). For triclosan tested concentrations were 100, 300, 500 and 700 mg/L and for carbendazim corresponded to 100, 165, 230, 295, 360 and 425 mg/L.…”