Effects of glyphosate formulations on the population dynamics of two freshwater cladoceran species.

The general objective of this work is to experimentally assess the effects of acute glyphosate pollution on two freshwater cladoceran species (Daphnia magna and Ceriodaphnia dubia) and to use this information to predict the population dynamics and the potential for recovery of exposed organisms. Five to six concentrations of four formulations of glyphosate (4-Gly) (Eskoba®, Panzer Gold®, Roundup Ultramax® and Sulfosato Touchdown®) were evaluated in both cladoceran species through acute tests and 15-day recovery tests in order to estimate the population dynamics of microcrustaceans. The endpoints of the recovery test were: survival, growth (number of molts), fecundity, and the intrinsic population growth rate (r). A matrix population model (MPM) was applied to r of the survivor individuals of the acute tests, followed by a Monte Carlo simulation study. Among the 4-Gly tested, Sulfosato Touchdown® was the one that showed higher toxicity, and C. dubia was the most sensitive species. The Monte Carlo simulation study showed an average value of λ always <1 for D. magna, indicating that its populations would not be able to survive under natural environmental conditions after an acute Gly exposure between 0.25 and 35 a.e. mg L-1. The average value of λ for C. dubia was also <1 after exposure to Roundup Ultramax®: 1.30 and 1.20 for 1.21 and 2.5 mg a.e. L-1,respectively. The combined methodology-recovery tests and the later analysis through MPM with a Monte Carlo simulation study-is proposed to integrate key demographic parameters and predict the possible fate of microcrustacean populations after being exposed to acute 4-Gly contamination events.

The impact of Eskoba, a glyphosate formulation, on the freshwater plankton community.

This study analyzed the acute effects of a glyphosate-based herbicide (Eskoba) on the microalgae Chlorella vulgaris, the cladoceran Simocephalus vetulus, and the copepod Notodiaptomus conifer, and evaluated the recovery ability of the surviving micro-crustaceans. Survival, age of first reproduction, and fecundity were used as endpoints for S. vetulus, while survival and time to reach the adult stage were used as endpoints for N. conifer. The registered order of sensitivity was S. vetulus (48-hour effective concentration [EC50]: 21 mg/L) > C. vulgaris (72-hour EC50: 58.59 mg/ L) > N. conifer (48-hour EC50: 95 mg/L). Despite the growth of C. vulgaris stimulated after 24 hours of exposure to the commercial formulation of glyphosate Eskoba, it was inhibited after 48 hours by all the concentrations tested. In postexposure experiments, microcrustaceans reduced their life expectancy, S. vetulus decreased its fertility, and N. conifer inhibited its sexual maturity. In summary, it was demonstrated that these species lost their recovery ability.

Chromium (Cr) accumulation in the freshwater crab, Zilchiopsis collastinensis.

The freshwater crab, Zilchiopsis collastinensis was exposed in vivo to determine Cr accumulation in visceral content. After an acclimation period we added Cr(K2Cr2O7) at nominal concentrations of 2 mg l(-1) Cr(VI) and 5 mg l(-1) Cr(VI) and a control (T0) under the same conditions, without Cr. At days 1, 7 and 14, Cr was measured in water sediments and crabs and the bioconcentration factor (BCF) in relation to water and to sediment were obtained. Considering all samples and all the study period, crabs registered 3 times more Cr than sediments and 18 times more Cr than water. Cr levels in Z. collastinensis tissues were always lower in the control than in T1 and T2; no significant differences among days 1, 7 and 14 were found in the control. In the treatments, no significant increase in Cr levels in tissues were found between days 1 and 7, neither between days 7 and 14 in both concentrations tested. Significant differences were found between the control and T1 and T2 (p<0.001), but not between T1 and T2. The highest BCF obtained for Z. collastinensis were 51.82 and 51.42 in T1 and T2 in water at 14 days of exposure. This study shows the efficiency of freshwater crabs to accumulate Cr from water.

Accumulation of chromium and interaction with other elements in Chlorella vulgaris (Cloroficeae) and Daphnia magna (Crustacea, Cladocera).

Assays with Chlorella vulgaris Beijerinck Novakova, 1890 and Daphnia magna Straus, 1820 were performed to determine Cr and other elements concentration in tissues of both species by instrumental neutron activation analysis (INAA), after being exposed to 150, 280 and 350 microg l(-1) Cr(VI). Interaction among Cu, Zn, Fe and Cr were also registered. In the control of C. vulgaris, the amount of Cr was < 4 microg g(-1); in the treatments with Cr(VI) the values were 47, 82 and 100 folds greater than the control for the lowest, intermediate and highest concentrations tested respectively. In the control of D. magna, the amount of Cr was <3 microg g(-1); in the treatments with Cr(VI) the values were 14, 13 and 27 folds higher than the control for the lower, intermediate and higher Cr(VI) concentrations respectively and from 3 to 9 times less than for C. vulgaris These results show that C. vulgaris is very efficient accumulator of Cr(VI) from polluted waters, and in consequence, it is proposed to be used in phytoremediation procedures.

Effects of Cu+2 and pH on the fitness of Ceriodaphnia dubia (Richard 1894) (Crustacea, Cladocera) in microcosm experiments.

An important disturbance of anthropogenic origin frequently occurring in freshwater ecosystems is a rise in the concentration of heavy metals in solution, among which copper stands out due to its known toxicity. However, the study of the chemical behavior of copper in solution is highly dependent on pH. In this study, the effect of ionic copper on the fitness of Ceriodaphnia dubia was assessed in microcosm experiments under different conditions of Cu+2 and pH. Two groups of experiments were conducted: effects on survival and fecundity, and effects on population dynamics. In the former, both pH and copper concentrations were manipulated. On the other hand, only the concentration of biologically available ionic copper was manipulated whereas pH was maintained constant in the population dynamics experiments. There was an agreement between both sets of experiments in terms of their results, showing important toxic effects of copper as evidenced through significant differences between controls and treatments in survival and fecundity. Mean age of first reproduction was delayed, and both the number of neonates produced per female and number of broods decreased with the increase in the concentration of copper. R0 was always lower at pH 6 than at pH 8 and was negatively related to the increment in the concentration of copper under either pH. A significant effect on population dynamics at 5 micrograms l-1 of copper sulfate was found and the extinction of the population at 20 micrograms l-1 of copper sulfate. New values of toxicity from copper are proposed, and the potential effects that an increment in copper could have on the communities that occupy a central position in aquatic food webs are discussed.