Environmental factors modify silver nanoparticles ecotoxicity in Chydorus eurynotus (Cladocera).

Silver nanoparticles (AgNPs) are among the most produced nanomaterials in the world and are incorporated into several products due to their biocide and physicochemical properties. Since freshwater bodies are AgNPs main final sink, several consequences for biota are expected to occur. With the hypothesis that AgNPs can interact with environmental factors, we analyzed their ecotoxicity in combination with humic acids and algae. In addition to the specific AgNPs behavior in the media, we analyzed the mortality, growth, and phototactic behavior of Chydorus eurynotus (Cladocera) as response variables. While algae promoted Ag+ release, humic acids reduced it by adsorption, and their combination resulted in an intermediated Ag+ release. AgNPs affected C. eurynotus survival and growth, but algae and humic acids reduced AgNPs lethality, especially when combined. The humic acids mitigated AgNP effects in C. eurynotus growth, and both factors improved its phototactic behavior. It is essential to deepen the study of the isolated and combined influences of environmental factors on the ecotoxicity of nanoparticles to achieve accurate predictions under realistic exposure scenarios.

The relative importance of salinization in lowland stream zooplankton: Implications of the ecosystem nutrient status.

Salinization of aquatic systems is predicted to increase due to climate and land use changes. Nevertheless, community responses may be different according to the ecosystem characteristics and contextual scenarios. Small flowing waters are particularly vulnerable to salinization, which may impact on the biodiversity and ecosystem processes, but this remains unclear. We conducted a study in 42 lowland streams characterized by overall high nutrient levels along a salinity gradient between 2 and 160 g L-1 to analyze changes in zooplankton structural and functional metrics, and the grazing effects of zooplankton on phytoplankton affecting the energy transfer. Generalized additive models revealed that the analyzed metrics were relatively influenced by salinity, with factors related to trophic conditions playing an important role as well. Total abundance and biomass decreased along the salinity gradient while increasing at intermediate soluble reactive phosphorous concentrations (SRP) in the former and with a linear increase in the SRP in the latter case. Taxonomic richness decreased with salinity and dissolved inorganic nitrogen, with species replacement toward saline-tolerant ones according to the compositional and optimums analyses. In opposite, functional richness did not display any specific trend within the environmental gradients. This explains why zooplankton compositional changes were not reflected into shifts in the grazing pattern on phytoplankton, which was in turn driven by SRP and dissolved oxygen concentrations. Further research is a critical requirement in these poorly studied ecosystems for planning mitigation actions to the co-occurrence of eutrophication and salinization in a fast changing world.

Effects of bifenthrin on microcrustaceans grazing behavior on a phytoplankton assemblage dominated by Cyanobacteria.

Insecticides are widely used for pest control and frequently reach aquatic systems, imposing a risk to the biota. In this work, the effect of environmental concentrations of bifenthrin on the grazing capacity of Simocephalus vetulus (Cladocera) and Argyrodiaptomus falcifer (Copepoda) on phytoplankton was evaluated. Fifteen microcrustacean individuals and a natural phytoplankton assemblage dominated by Cyanobacteria were exposed during 46 h to three concentrations of bifenthrin (C0 0 µg L-1, C1 0.02 µg L-1, and C2 0.05 µg L-1). A significant decrease in both microcrustaceans grazing rates on total phytoplankton was observed in C2 compared to C0 and C1. The filtration rate (ml ind-1 h-1) of S. vetulus decreased significantly for the cyanobacteria Anabaenopsis arnoldii, Dolichospermum circinale, and Glaucospira sp. in C2 compared to C0 and C1. The ingestion rate (org ind-1 h-1) of A. falcifer decreased significantly in C1 and C2 compared to C0 only for A. arnoldii. Regarding phytoplankton morphological groups, the filtration rate of S. vetulus decreased in C1 and C2 compared to C0 for Colonies and Coenobiums in C2 concerning C0 and C1 for Filaments and in C2 compared to C0 for Silicified. For A. falcifer, the ingestion rate was reduced in C2 compared to C0 for Silicified, Flagellated, and Sessile. The results showed that bifenthrin affected both microcrustaceans grazing capacity on phytoplankton, especially at the highest insecticide concentration.

Nanosilica size-dependent toxicity in Ceriodaphnia reticulata (Cladocera).

Silica nanoparticles (SiNP) are the most produced nanomaterials due to their variety of applications. When released to environments, surface water bodies are their main final sink. SiNP toxicity is still inconclusive and may vary according to particle properties such as their size. We analyzed the size-related effects of SiNP (22 and 244 nm) on mortality, life history traits, and oxidative stress in the cladoceran Ceriodaphnia reticulata. The smaller SiNP (LC5072 h: 105.5 µg/ml) were more lethal than the larger ones (LC5072 h >500 µg/ml). The 22 nm-sized SiNP decreased the number of molts and neonates, increased superoxide dismutase and inhibited glutathione S-transferase activities, while larger SiNP did not exert substantial effects on the organisms at the tested concentrations. In conclusion, SiNP toxicity depended on their size, and this information should be considered for regulatory purposes and to the development of safe-by-design nanoproducts to ultimately guarantee the environment protection.

Ecotoxicity of nanosilver on cladocerans and the role of algae provision.

Silver nanoparticles (AgNPs) are applied in diverse industries due to their biocide and physicochemical properties; therefore, they can be released into aquatic systems, interact with environmental factors, and ultimately exert adverse effects on the biota. We analyzed AgNPs effects on Ceriodaphnia reticulata (Cladocera) through mortality and life-history traits, considering the influence of food (Tetradesmus obliquus, Chlorophyceae) presence and concentration. C. reticulata was exposed to AgNPs in acute (absence and two algae concentrations plus five AgNPs treatments) and chronic assays (two algae concentrations plus three AgNPs treatments). AgNPs did not affect algae flocculation but increased Ag+ release, being these ions less toxic than AgNPs (as proved by the exposure to AgNO3). A reduction in AgNPs acute toxicity was observed when algae concentration increased. Acute AgNP exposure decreased C. reticulata body size and heart rate. The chronic AgNP exposure reduced C. reticulata molt number, growth, heart rate, and neonate size:number ratio, being these effects mitigated at the highest algae concentration. Increases in relative size and number of neonates were observed in AgNP treatments suggesting energy trade off. The increased Ag+ release with food presence suggests that the AgNP-algae interaction might be responsible of the decreased toxicity. Although algae reduced AgNP toxicity, they still exerted adverse effects on C. reticulata below predicted environmental concentrations. Since algae presence reduces AgNP effects but increases Ag+ release, studies should be continued to provide evidence on their toxicity to other organisms.

Effect of rainfall runoff from agricultural areas and seasonal crop practices on zooplankton community in Pampean streams, Argentina.

Extreme climatic events are considered one of the main consequences of climate change. In the Pampas region, Argentina, an intensification of rainfall is expected during the periods of maximum agrochemical application. This study assesses the main factors determining the zooplankton community attributes in three streams belonging to the agricultural Pampas region, Argentina, and the effect of rainfall and seasonal crop practices on the zooplankton community composition. Sampling campaigns were performed before and after three rainfall events during two seasonal crop practices: (1) soybean chemical fallow-sowing and corn vegetative growth-flowering, (2) soybean vegetative growth-grain filling and corn sowing. The runoff in agricultural areas affected the zooplankton community attributes and composition. The biological oxygen demand, turbidity, and conductivity were the main water quality variables affecting the zooplankton community attributes. The increase of these variables after rainfall or during pre-emergence crop practices favoured the zooplankton groups most tolerant to eutrophication such as Bdelloidea, Chydoridae, Moinidae, and Sididae. Factors such as rainfall and seasonal crop practices must be considered in environmental monitoring design.

Influence of rainfall and seasonal crop practices on nutrient and pesticide runoff from soybean dominated agricultural areas in Pampean streams, Argentina.

An increase in the spatial variability of rainfall is expected due to climate change. This implies increasing rainfall rates during spring and summer in the Pampas region, Argentina, period of maximum application of agrochemicals, which might cause an increase in pesticides and nutrients carried to surface water systems, as runoff by rainfall is one of the main pathways for diffuse pollution. The crops phenological stage can also affect pesticide and nutrient runoff since the applied agrochemicals and soil cover differ in each stage. In this study, we assessed the influence of rainfall and seasonal crop practices on water quality (nutrient and pesticide concentrations) in three streams in the Pampas region, Argentina. Five sampling campaigns were performed before and after three rainfall events during two different seasons of crop practices (SCP1, SCP2) and the physicochemical characteristics of the stream and runoff water were analyzed. The pesticide concentrations in the streams presented a general increase immediately after the rainfall event. Water quality was also affected, as an increase in ammonium, soluble reactive phosphorus (SRP), biological oxygen demand (BOD), and turbidity was observed. The crops phenological stage influenced pesticide and nutrient types and concentrations detected in the streams. During SCP1, mainly characterized by chemical fallow and sowing of soybean and vegetative growth and flowering of corn, ammonium, SRP, BOD, turbidity, and some pesticides, such as metolachlor, showed significantly higher results than those found in SCP2 (grain filling and vegetative growth of soybean and corn sowing). The pesticide concentrations detected in runoff water depended mostly on the pesticide solubility, the lateral slope of the streams, and the percentage of woody riparian vegetation cover. The results obtained show the relevance of assessing the influence of rainfall and crops phenological stages on the dynamics of surface water and on pesticide and nutrient runoff for environmental monitoring.

Synergy between glyphosate and cypermethrin formulations on zooplankton: evidences from a single-specie test and a community mesocosm experiment.

Agrochemicals can reach freshwater bodies by drift, leaching, or runoff, where they constitute complex mixtures. Given that glyphosate and cypermethrin are within the most worldwide used pesticides, they are likely to co-occur in freshwater bodies. The aim of this study was to analyze the interaction between glyphosate and cypermethrin formulations on the cladoceran Ceriodaphnia dubia (Richard 1894) through an acute toxicity test and on a zooplankton assemblage through a mesocosm (30 L) experiment. The 24-h LC50 of both isolated pesticides and their equitoxic mixture was obtained for C. dubia. The mesocosm was performed by exposing a zooplankton assemblage to both pesticides isolated and in combination. The acute toxicity of the equitoxic mixture in C. dubia was 3 and 4 times higher than the isolated toxicity of glyphosate and cypermethrin, respectively. The total toxic units of the mixture were 0.53, indicating a synergistic interaction. In the mesocosm experiment, both pesticides also interacted causing a synergistic negative effect in Cladocera and Copepoda abundances. No interactions between pesticides were found for Rotifera; therefore, the mixture effect was considered additive. It is suggested to continue analyzing pesticide mixture effects on the basis of complementary scales of analysis to reach more environmentally relevant information.

How can interspecific interactions in freshwater benthic macroinvertebrates modify trace element availability from sediment?

This study aimed to assess how bioturbation by freshwater benthic macroinvertebrates with different biological traits alone or in combination could modify trace elements (TE) fate between sediment and water, and if water TE concentration and animal TE content impair their body stores. Three macroinvertebrate species were exposed to TE contaminated sediment for 7 days: the omnivorous Echinogammarus berilloni (Amphipoda), the sediment feeding Tubifex tubifex (Oligochaeta) and the filter feeding Pisidium sp. (Bivalvia). Treatments were one without invertebrates (control), two with amphipods or mussels alone, and the combinations amphipod-mussel, and amphipod-mussel-worms. Water TE concentration increased significantly in 2 or 3 species mesocosms, concerning mainly Rare Earth Elements, Cr, U and Pb, known to be associated to the colloidal phase. By contrast, water soluble TE were not affected by animals. For both, amphipods and mussels, TE body content increased with the number of coexisting species. For amphipods, this increase concerned both, soluble and colloid-associated TE, possibly due to intense contact and feeding from sediment and predation on tubificids. TE bioaccumulation in mussel was less important and characterized by soluble TE, with water filtration as most plausible uptake route. Protein, triglyceride and Whole Body Energy Budget increased in amphipods with the number of coexisting species (probably by feeding on mussels' feces and tubificids) whereas triglycerides declined in mussels (presumably filtration was disturbed by amphipods). This study highlights interspecific interactions as key drivers explaining both: TE bioturbation, depending on their water solubility or colloidal association, and the exposure/contamination of species through another species activity.