Propylparaben is widely used as a preservative in pharmaceuticals and personal care products and is ultimately excreted by the human body. Thus, propylparaben reaches sewage and enters the soil environment by sludge fertilization and wastewater irrigation. However, there are few existing studies on the toxicity and risks of such chemicals in terrestrial environments. In this study, a multispecies bioassay for propylparaben was performed and protective concentrations (PCs) were derived based on toxicity values by probabilistic ecological risk assessment. Acute and chronic bioassays were conducted on 11 species in eight taxonomic groups (Magnoliopsida, Liliopsida, Clitellata, Entognatha, Entomobryomorpha, Chromadorea, Chlorophyceae, Trebouxiophyceae). Based on the toxicity values calculated, the PC₉₅ values for acute and chronic SSDs were 13 and 6 mg/kg dry soil, respectively. Toxicity varied among taxa, with soil algae emerging as the most sensitive to propylparaben. This may be attributable to differences in exposure pathways among species. The exposure pathway of propylparaben can be altered by adsorption to soil particles. As parabens are presently under-regulated globally in terms of their environmental effects, our findings can serve as the basis to propose standard values for environmental protection.

In the environment, microalgae are exposed to a multitude of stressors simultaneously, inducing physiological adjustments. It is well documented that both phosphorus (P) limitation and trace metals exposure affect microalgal physiology. However, investigations regarding the combination of both P limitation and excess trace metals still deserve attention. In the present study, we evaluated the changes in photosynthetic parameters in the green microalga Ankistrodesmus densus acclimated to different P concentrations prior to exposure to Cd. Our results indicate that different concentrations of P in the medium were responsible for significant changes in some parameters, especially those related to photoprotection mechanisms. Cadmium also altered some of these variables in all P scenarios, and greater damage (i.e., synergism) was observed in the combination P-limited and high Cd, with all the evaluated parameters affected under the adverse scenario. Among the parameters analyzed, rapid light curves were the most sensitive to exposure of one or the combination of both stressors (Cd and P limitation). Based on our data, we suggest that P-limited algae activated photoprotective mechanisms as a response to nutrient limitation, especially at the most limited condition. The addition of Cd did not change linearly the parameters related to photoprotection mechanisms under P-limitation, i.e., synergism was observed in the intermediate P-limitation combined with Cd, while in the most P-limited, P seems to be the driving force affecting these mechanisms. Based on our results, we suggest the use of rapid light curves as a tool to complement the assessment of the impacts of stressors, such as metals, in ecotoxicological studies.

The aim of this study was to analyze the density, diversity, biomass and assemblage composition of the phytoplankton in relation to environmental conditions (physical, chemical, hydrological and meteorological variables), measured under the different scenarios caused by the ENSO phenomenon in the period between 2005 and 2012, in six sampling sites in the tidal freshwater zone of the Río de la Plata estuary, covering almost 100km of coastline. The results revealed changes in the structure of the phytoplankton, such as a significant reduction of diversity, and decreases in biomass and phytoplankton density, particularly during El Niño phases. Cyanobacteria were more abundant in the neutral periods, Chlorophyceae dominated La Niña phase while Bacyllariophyceae dominated El Niño. However, no complete replacement of species between cycles was observed. The results obtained were highly variable due to the inherent natural variability of the Río de la Plata, emphasized by the anthropogenic impact in this area.

A literature review on the effects of high ammonium concentrations on the growth of 6 classes of microalgae suggests the following rankings. Mean optimal ammonium concentrations were 7600, 2500, 1400, 340, 260, 100μM for Chlorophyceae, Cyanophyceae, Prymnesiophyceae, Diatomophyceae, Raphidophyceae, and Dinophyceae respectively and their tolerance to high toxic ammonium levels was 39,000, 13,000, 2300, 3600, 2500, 1200μM respectively. Field ammonium concentrations <100μM would not likely reduce the growth rate of most microalgae. Chlorophytes were significantly more tolerant to high ammonium than diatoms, prymnesiophytes, dinoflagellates, and raphidophytes. Cyanophytes were significantly more tolerant than dinoflagellates which were the least tolerant. A smaller but more complete data set was used to estimate ammonium EC50 values, and the ranking was: Chlorophyceae>Cyanophyceae, Dinophyceae, Diatomophyceae, and Raphidophyceae. Ammonia toxicity is mainly attributed to NH3 at pHs >9 and at pHs <8, toxicity is likely associated with the ammonium ion rather than ammonia.

Given the authoritative and well-documented publication records that crenic habitats support the substantial aquatic biodiversity, understanding of algal dynamics in response to anthropogenic and natural stressors in these crenic systems seems paramount. We sampled and monitored twelve freshwater springs for a period of 2 years from 2014 to 2015 to observe algal dynamics and the factors govern the distribution and dynamics. We used ANOVA, nMDS, PCA, ANOSIM, SIMPER, and BIOENV to reveal the key physicochemical variables influencing the distributional pattern and dynamics of algae. The analysis of variance (ANOVA, Tukey’s post hoc test) revealed significant difference among the springs with dominance of Bacillariophyceae (62%) followed by Chlorophyceae (18%) whereas nMDS ordination of abundance data in two-dimensional space resulted in a significant separation between spring sites (stress value of 0.13). One-way nested ANOSIM produced a significant distinction between periphytic algal communities in springs (global test R = 0.928, p = 0.001). The results of SIMPER revealed the highest average dissimilarity (60.95%) between springs S4 and S5, with the top five contributing families including Cyanophyceae (30.25%), Bacillariophyceae (25.98%), Rhodophyceae (16.74%), Chlorophyceae (13.64%), and Chrysophyceae (13.39%). BIOENV analysis of the periphytic algal data suggested that the assemblage pattern in all crenic habitats were controlled by discharge, conductivity, dissolved oxygen, total alkalinity, and total phosphorus. Since, springs are groundwater-dependent ecosystems acting as ecohydrologic refugia, any small change in groundwater discharge could strongly influence the ambient conditions (including water quality and temperature), which in turn influences the biological assemblage patterns and ecosystem services. Therefore, changes in discharge may provide information on possible future ecological change in the springs in relation to rising aridification.

Commercial usage of ZnO nanoparticles has increased recently due to its versatile applications, raising serious environmental concern because of its ultimate release of nanoparticles in aquatic ecosystem. Therefore, it is important to understand the impact of ZnO nanoparticle toxicity especially on algal flora, which is the primary producer in the aquatic food chain. In the current study, algal growth kinetics was assessed after the exposure of zinc oxide nanoparticles and its bulk counterpart to Coelastrella terrestris (Chlorophyceae). Zinc oxide nanoparticles were found to be more toxic (y = 34.673x, R² = − 0.101, 1 mg L⁻¹ nanoparticle (NP)) than bulk (y = 50.635x, R² = 0.173, 1 mg L⁻¹ bulk) by entrapping the algal cell surface. Higher toxicity may be due to oxidative stress within the algal cell as confirmed through biochemical analysis. Biochemical parameters revealed stressful physiological condition in the alga under nanoparticle exposure, as lactate dehydrogenase release (18.89 ± 0.2 NP; 13.67 ± 0.2 bulk), lipid peroxidation (0.9147 ± 1.2 NP; 0.7480 ± 0.8 bulk), and catalase activity (4.77 ± 0.1 NP; 3.32 ± 0.1 bulk) were found higher at 1 mg L⁻¹ in the case of nano-form. Surface adsorptions of nanoparticles were observed by SEM. Cell organelle damage, cell wall breakage, and cytoplasm shrinkage were found as responses under toxic condition through SEM and TEM. Toxicity was found to be influenced by dose concentration and exposure period. This study indicates that nano-form of ZnO is found to be more toxic than bulk form to freshwater alga.

Biological evaluation is a useful alternative for rating the ecological quality of aquatic ecosystems, as biological communities amalgamate the environmental effects of water chemistry. To recognize the nature of species composition of phytoplankton and their significance, the present surveillance was made for a period of twelve months in a sacred water body in Belgaum district. The study exposed the occurrence of 50 phytoplankton species belonging to 26 genera. Among these, 19 genera are identified as most pollution tolerant genera. According to the list, dominant group was represented by Bacillariophyceae followed by Chlorophyceae and Euglenophyceae. The algal flora of this sacred water body showed the dominance of Scenedesmus, Pediastrum, Ankistrodesmus, Coelastrum, Cyclotella, Navicula, Nitzschia, Synedra, Melosira, Euglena, Lepocinclis and Phacus. These floating, inconspicuous primary producers of aquatic ecosystem are indicators of organic pollution. The present paper highlights the assessment of water quality status using pollution index based on the phytoplankton community of water.