Exposure to sublethal chromium and endosulfan alter the diel vertical migration (DVM) in freshwater zooplankton crustaceans

Unveiling the multilevel impact of four water-soluble polymers on Daphnia magna: From proteome to behaviour (a case study)

The ubiquitous presence of water-soluble polymers (WSPs) in freshwater environments raises concerns regarding potential threats to aquatic organisms. This study investigated, for the first time, the effects of widely used WSPs -polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyethylene glycol (PEG)- using a multi-level approach in the freshwater biological model Daphnia magna. This integrated assessment employed a suite of biomarkers, evaluation of swimming behaviour, and proteomic analysis to investigate the effects of three environmentally relevant concentrations (0.001, 0.5, and 1 mg/L) of the tested WSPs from molecular to organismal levels, assessing both acute and chronic effects. Our findings reveal that exposure to different WSPs induces specific responses at each biological level, with PEG being the only WSP inducing lethal effects at 0.5 mg/L. At the physiological level, although all WSPs impacted both swimming performance and heart rate of D. magna specimens, PAA exhibited the greatest effects on the measured behavioural parameters. Furthermore, proteomic analyses demonstrated altered protein profiles following exposure to all WSPs, with PVA emerging as the most effective.

Ecotoxicological Effects of Potassium Dichromate on the Tadpole Shrimp Triops longicaudatus

The tadpole shrimp Triops longicaudatus is a freshwater crustacean with fast embryonic and larval development, short life cycle, and high fecundity. They are very active swimmers of a reasonable size, easy to spot and record. Such characteristics make it a promising candidate as an experimental model in ecotoxicology to evaluate the effects of aquatic pollutants, particularly using its locomotor behavior as an endpoint. To evaluate the sensitivity of T. longicaudatus and develop endpoints of interest, we conducted exposure experiments with lethal and sub-lethal concentrations of potassium dichromate, a compound known for its ecotoxicological importance and as a hexavalent chromium source. The endpoints evaluated were mortality, growth, sexual maturation, reproductive output, cholinesterase activity and locomotor/swimming behavior. The 96 h median lethal concentration was found to be 65 µg/L. Furthermore, exposure to potassium dichromate at higher concentrations had a significant negative impact on the growth rate of T. longicaudatus in terms of both body mass and length. The time for maturation was also delayed at higher concentrations. In addition, locomotor behavior allowed for the discrimination of all tested chromium concentrations and the control group and from each other, proving to be the most sensitive endpoint. Overall, the data support the potential of T. longicaudatus as a model for ecotoxicity testing, using apical endpoints with impact at the population level; in particular, results suggest that behavior assessments in this species might be useful for detecting hazardous compounds in environmental monitoring of freshwater ecosystems.

Freshwater salinization reduces vertical movement rate and abundance of Daphnia: Interactions with predatory stress

Contaminants in human-dominated landscapes are changing ecological interactions. The global increase in freshwater salinity is likely to change predator-prey interactions due to the potential interactive effects between predatory stress and salt stress. We conducted two experiments to assess the interactions between the non-consumptive effects of predation and elevated salinity on the abundance and vertical movement rate of a common lake zooplankton species (Daphnia mendotae). Our results revealed an antagonism rather than a synergism between predatory stress and salinity on zooplankton abundance. Elevated salinity and predator cues triggered a >50% reduction in abundance at salt concentrations of 230 and 860 mg Cl^-/L, two thresholds designed to protect freshwater organisms from chronic and acute effects due to salt pollution. We found a masking effect between salinity and predation on vertical movement rate of zooplankton. Elevated salinity reduced zooplankton vertical movement rate by 22-47%. A longer exposure history only magnified the reduction in vertical movement rate when compared to naïve individuals (no prior salinity exposure). Downward movement rate under the influence of predatory stress in elevated salinity was similar to the control, which may enhance the energetic costs of predator avoidance in salinized ecosystems. Our results suggest antagonistic and masking effects between elevated salinity and predatory stress will have consequences for fish-zooplankton interactions in salinized lakes. Elevated salinity could impose additional energetic constraints on zooplankton predator avoidance behaviors and vertical migration, which may reduce zooplankton population size and community interactions supporting the functioning of lake ecosystems.

Effects of glyphosate on cladocera: A synthetic review

Glyphosate [N-(phosphonomethyl) glycine] is currently the most widely used herbicide worldwide. Its application in agricultural and urban areas can lead to the dispersion and arrival to aquatic systems causing environmental deterioration with detrimental effects on the inhabiting biota. This is triggered not only by the herbicide per se but also its metabolite aminomethyl-phosphonic acid (AMPA), which can be highly toxic to many aquatic organisms. Water fleas are some of the key components in aquatic food webs, being one of the most sensitive groups to pollutants. Although being often used in standardized toxicity tests, they are comparatively less studied in relation to glyphosate exposition. Here we examine the current scientific literature regarding the acute and sublethal toxicity of glyphosate in the Cladocera taxonomic group, with special comparisons between the active ingredient (A.I) and formulations. Our results document a high variation in the lethal concentrations reported for different cladoceran species, due to the high diversity of products used in the toxicity tests. Most articles accounting for sublethal effects were performed on the standard Daphnia magna species. Reproduction, including decreased fecundity and delayed age of first reproduction, is usually one of the most severely affected individual traits. Although still scarce, studies documenting metabolic and genetic alterations might provide accurate information on the mechanisms of action of the herbicide.

Vertical distribution of microplastics in water bodies causes sublethal effects and changes in Daphnia magna swimming behaviour

Plastic debris has been found to be ubiquitous in many aquatic ecosystems and is constantly accumulating, not only because more and more plastic is being rapidly released into the environment, but also because its slow degradation means it persists in the water. Some more buoyant plastics accumulate in the water column, whereas other heavier types sink to the bottom. Consequently, the presence of microplastics can threaten organisms living in the water column as well as those found in the benthic zone. In this study, the filter feeder Daphnia has been found to ingest microplastics as the particle diameter (< 30 µm) is within their edible particle size range and they are unable to differentiate between particles of different natures. Four different treatments were considered: food only; only microplastic particles; 50% food and 50% microplastic particles; neither food nor microplastics. Sinking microplastics have been found to decrease Daphnia magna individuals' swimming velocity during vertical or cruising swimming trajectories, therefore demonstrating the sublethal effects microplastics have on this organism. In addition, microplastics decreased their body growth and survival rates. In cases with the presence of only microplastics, the swimming trajectories of Daphnia indicated the most serious stress experienced as individuals reversed vertical or cruising swimming trajectories to hopping and sinking movements. Therefore, Daphnia individuals in freshwater systems polluted by microplastics might take on the role of ingesting them and later on transporting them to deeper layer water column. In this way microplastics that would remain in the water column for a long time due to their buoyancy, might accumulate at the bottom of the water column.

A comprehensive system for detection of behavioral change of D. magna exposed to various chemicals

The purpose of the present study was to develop a sensitive and comprehensive method, based on D. magna swimming behavior, for toxicity assessment of environmental chemicals. Firstly, D. magna swimming in several chambers with different diameters were compared to determine the most suitable container, and then baseline behaviors during light/dark periods as well as reactions to light/dark switching and vibration stimulation were determined. Secondly, after exposure to sub-lethal concentrations of the selected 42 typical chemicals, which were classified into heavy metals, pesticides, fungicides and flame retardants, the alterations in the swimming parameters were evaluated. Our results indicated the 48-well plate was the most suitable chamber for behavioral monitoring of D. magna, and specific responsive patterns of D. magna neonates to light/dark switching and vibration stimulation were observed. The results of the behavioral assays of chemicals suggested that D. magna was the most sensitive to methylmercury-chloride and then to abamectin and chlorpyrifos. The three chemicals at several to dozens of ng/L significantly changed swimming behaviors of D. magna. Furthermore, the alteration in the behavioral parameters (average swimming speed, etc.) induced by the selected chemicals could be ascribed to various modes of actions, confirming the reliability and practicability of the monitoring method.

Water and sediment quality assessment in the Colastiné-Corralito stream system (Santa Fe, Argentina): impact of industry and agriculture on aquatic ecosystems

The present study focuses on the evaluation of metal (chromium, copper, and lead), arsenic, and pesticide (atrazine and endosulfan) contamination in freshwater streams of one of the most important agricultural and industrial areas of central-eastern Argentina, which has not been reported earlier. The environmental fate of inorganic microcontaminants and pesticides was assessed. Samples were collected monthly for a year. Pesticide concentrations were measured in water; metal and arsenic concentrations were measured in water and sediments, and physicochemical variables were analyzed. In most cases, metals and arsenic in water exceeded the established guideline levels for the protection of aquatic biota: 98 and 56.25% of the samples showed higher levels of Cr and Pb, while 81.25 and 85% of the samples presented higher values for Cu and As, respectively. Cr, Pb, Cu, and As exceeded 181.5 times, 41.6 times, 57.5 times, and 12.9 times, respectively, the guideline level values. In sediment samples, permitted levels were also surpassed by 40% for Pb, 15% for As, 4% for Cu, and 2% for Cr. Geoaccumulation Index (Igeo) demonstrated that most of the sediment samples were highly polluted by Cr and Cu and very seriously polluted by Pb, which indicates progressive deterioration of the sediment quality. Atrazine never exceeded them, but 27% of the 48 water samples contained total endosulfan that surpassed the guidelines. The findings of this study suggest risk to the freshwater biota over prolong periods and possible risk to humans if such type of contaminated water is employed for recreation or human use. Improper disposal of industrial effluents and agricultural runoffs need to be controlled, and proper treatment should be done before disposal to avoid further deterioration of the aquifers of this area.

Daphnia swimming behaviour as a biomarker in toxicity assessment: A review

Daphnia is a motile common model organism widely used in ecotoxicological testing. Although mortality and immobilisation are the main endpoints used for determination of toxicity, detection of subtle alterations induced by some chemicals particularly at lower levels may require more sensitive biomarkers. As a number of studies indicated that swimming behaviour may be altered by pesticides, nanoparticles, bacterial products or other chemicals, analysis of its various parameters is considered as a novel methodological approach for toxicity assessment and monitoring of water quality. This paper presents the current state of knowledge on the effects induced by various chemical compounds on the parameters of swimming behaviour of Daphnia and systems developed for its analysis. Advantages and limitations of swimming behaviour as a tool in toxicological studies are also discussed.

Monitoring and quantification of the complex bioaccumulation process of mercury ion in algae by a novel aggregation-induced emission fluorogen

In this study, a novel methodology was developed using a specified aggregation-induced emission fluorogen (AIEgen) to monitor and quantify the complex bioaccumulation process in a microcosm aquatic ecosystem.

The effect of primary producers of experimental aquatic food chains on mercury and PCB153 biomagnification

The biomagnification of mercury and PCB153 was studied in experimental aquatic food chains involving three species of phytoplankton, one species of zooplankton and one species of fish. The phytoplankton species Ceratium furca, Ceratium tripos and Chaetoceros brevis were exposed to 0, 0.2, 0.5, 1.0 and 2.0 mg/l of Hg and 0, 0.5 and 2.0 mg/kg of PCB 153. Subsequently, each species was fed to the zooplankton Daphnia hyaline, which was then used as food for the fish Liza abu. The results indicated biomagnification of Hg and PCB153 in all three chains. Highest concentration of mercury was found in C. brevis and the highest concentration of PCB153 was observed in C. tripos. Accordingly, highest concentration of Hg and PCB 153 was found in D. hyaline and in the liver of L. abu belonging to food chains started from Chaetoceros brevis and Ceratium tripos respectively.

Infodisruptions in predator-prey interactions: xenobiotics alter microcrustaceans responses to fish infochemicals

Chemical communication is one of the most important ecological phenomena promoting the maintenance of ecosystem dynamics. In predator-prey interactions, mediation signals allow prey to detect their predators and can be crucial in the process of avoiding them. Since organisms in many natural waterbodies are often subjected to anthropogenic stressors, it is hypothesised that low concentrations of xenobiotic compounds can disturb this chemical communication, acting as infodisruptors. This study analyzes whether two anthropogenic pollutants (chromium and an insecticide) interfere in two freshwater predator-prey interactions, by altering the behavioural responses of a cladoceran and a copepod species to a fish chemical cue. The concentrations tested were lower than those considered innocuous under international water quality guidelines, and two types of behaviour were analysed: escape ability and depth selection in an artificial water column. Both species tested demonstrated a higher escape ability when exposed to the cue than when they were not exposed. Xenobiotics modified the responses of the copepod in opposite ways: chromium inhibited this behaviour and the insecticide prompted a higher than expected level of escape ability. The depth selection patterns were different between N. conifer and C. dubia. Fish kairomones did not modify them, however chromium and the insecticide caused important alterations in both cases. Such disruptions would be detrimental to the organisms' life cycle trajectories, which, in natural systems, would cause longterm damage in trophic structure and in evolutionary processes.