Metal-organic frameworks (MOFs) are an emerging class of materials which have garnered increasing attention for their utility as adsorbents and photocatalysts in water treatment. Nevertheless, the environmental risks of MOFs, especially their underlying impacts on aquatic organisms, are not fully explored. Herein, the toxicity of multiple representative MOFs was systematically assessed using a freshwater green alga (Chlamydomonas reinhardtii) model. Six typical MOFs with different metal nodes or organic linkers, including four transition metal incorporated aluminum-based porphyrin MOFs [pristine Al-PMOF, Al-PMOF (Cu), Al-PMOF (Ni), and Al-PMOF (Co)], one amine-functionalized MOF NH₂-MIL-125 (Ti), and one bimetallic Hofmann MOF (NiCo-PYZ), were successfully synthesized and characterized. All the tested MOFs significantly reduced the chlorophyll content and inhibited the algal growth, with the most toxic materials being NiCo-PYZ and Al-PMOF (Cu). Distinct toxic mechanisms were observed for the tested MOFs. Metal ion release was the primary cause for algal toxicity induced by NiCo-PYZ. The algal toxicity induced by porphyrin MOFs could be explained by the combined effects of metal ion release and nutrient adsorption, agglomeration and physical interactions, and reactive oxygen species generation. NH₂-MIL-125 (Ti) showed higher stability and more biocompatibility than the other tested MOFs. MOFs concentrations with no harmful effects to algae can be taken as the threshold values for safe use and discharge of MOFs. The ecotoxicological risks of MOFs should be considered as the applied concentrations of MOFs at mg/mL levels in environmental remediation were much higher than the no harmful effect thresholds.

Microalgae are widely used as representative primary producers in ecotoxicology, while macrophytes are much less studied. Here we compared the bioavailability and cellular toxicity pathways of 2 h-exposure to 10−6 mol L−1 Cu in the macrophyte Elodea nuttallii and the green microalga Chlamydomonas reinhardtii.Uptake rate was similar but faster in the algae than in the macrophyte, while RNA-Sequencing revealed a similar number of regulated genes. Early-regulated genes were congruent with expected adverse outcome pathways for Cu with Gene Ontology terms including gene regulation, energy metabolism, transport, cell processes, stress, antioxidant metabolism and development. However, the gene regulation level was higher in E. nuttallii than in C. reinhardtii and several categories were more represented in the macrophyte than in the microalga. Moreover, several categories including oxidative pentose phosphate pathway (OPP), nitrate metabolism and metal handling were only found for E. nuttallii, whereas categories such as cell motility, polyamine metabolism, mitochondrial electron transport and tricarboxylic acid cycle (TCA) were unique to C. reinhardtii. These differences were attributed to morphological and metabolic differences and highlighted dissimilarities between a sessile and a mobile species. Our results highlight the efficiency of transcriptomics to assess early molecular responses in biota, and the importance of studying more aquatic plants for a better understanding on the impact and fate of environmental contaminants.

In the present study, we evaluate our previously developed non-destructive soil algal toxicity method using species from a different class of algae; Class Trebouxiophyceae (Chlorella vulgaris and Chlorella sorokiniana), and directly measure the photosynthetic activity of these species adsorbed onto the soil as a new toxicity endpoint. This study shows that non-destructive soil algal toxicity method is applicable to non-specific test species, including those of Class Trebouxiophyceae as well as Class Chlorophyceae (Chlorococcum infusionum and Chlamydomonas reinhardtii). Furthermore, by performing photosynthesis image analysis, we verify that it is possible to measure the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soils without the need to extract algal cells from the soil. We propose that the non-destructive soil algal toxicity method represents a novel technique for 1) evaluating pollutants in soil using non-specific algae and 2) conveniently and rapidly assessing the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soil as a new toxicity endpoint.

In this study, the accumulation and toxicity effect of 1–7 μM of Hg was determined during 24–72 h on two strains of Chlamydomonas reinhardtii, CC-125 and CC-503 as a cell wall-deficient mutant, by monitoring the growth rate and the maximum quantum yield of Photosystem II. In addition, the level of extracytoplasmic polyphosphates (polyP related to the cell wall) was determined to understand the polyP physiological role in Hg-treated algal cells. The results showed that the polyP level was higher in the strain CC-125 compared to CC-503. When algal cells were exposed to 1 and 3 μM of Hg, the accumulation of Hg was correlated with the degradation of polyP for both strains. These results suggested that the degradation of polyP participated in the sequestration of Hg. In fact, this mechanism might explain at 72 h the recovery of the polyP level, the efficiency of maximum PSII quantum yield, the low inhibition of growth rate, and the low accumulated Hg in algal biomass. Under the effect of 5 and 7 μM of Hg, the degradation of polyP was complete and could not be recovered, which was caused by a high accumulation and toxicity of Hg already at 24 h. Our results demonstrated that the change of polyP level was correlated with the accumulation and effect of Hg on algal cells during 24–72 h, which can be used as a biomarker of Hg toxicity. Therefore, this study suggested that extracytoplasmic polyP in C. reinhardtii contributed to the cellular tolerance for Hg.

The phenolic compounds have posed public concern for potential threats to human health and ecosystem. Tert-butylphenols (TBPs), as one group of emerging contaminants, showed potential endocrine disrupting effects and aquatic toxicities. In the present study, we detected concentrations of 2,4-DTBP ranging from <0.001 to 0.057 μg/L (detection limit: 0.001 μg/L) in drinking water source from the Qiantang River in East China in April 2016. The endocrine disrupting effects of 2-TBP, 2,4-DTBP and 2,6-DTBP toward human estrogen receptor α (ERα), androgen receptor (AR) and thyroid hormone receptor β (TRβ) were evaluated using human recombinant two-hybrid yeast bioassay. Their aquatic toxicities were investigated with indicator organisms including Photobacterium phosphoreum, Vibrio fischeri and freshwater green alga Chlamydomonas reinhardtii. 2-TBP and 2,4-DTBP exhibited moderate antagonistic effects toward human ERα and AR in a concentration-dependent manner. 2-TBP significantly inhibited the light emission of P. phosphoreum. 2-TBP, 2,4-DTBP and 2,6-DTBP significantly inhibited the growth of C. reinhardtii and reduced the chlorophyll content. Our results suggest the potential adverse effects of TBPs on human health and aquatic organisms. The data will facilitate further risk assessment of TBPs and related contaminants.

Soil algal bioassays have been limited by their inability to evaluate several toxic endpoints because it is difficult to collect pure soil algae growing on and beneath the soil surface. This study describes the extension of a previously developed paper-disc method for analyzing soil toxicity to algae. The method can be used in conjunction with flow cytometric analysis and facilitates the assessment of previously proposed toxicity endpoints, such as the growth zone, biomass, and photosynthetic activity. We assessed the applicability of this paper-disc soil method using the green algae Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata exposed to nickel-contaminated soil; examined cell sizes, cell granularity, enzyme activity, and oxidative stress as new toxicity endpoints using flow cytometry; and identified morphological changes in green algae assayed. The results showed that, used in conjunction with flow cytometry, the extended paper-disc soil method is sufficiently sensitive to detect decreases in cell granularity in C. reinhardtii and esterase activity in P. subcapitata. The method also revealed decreases in growth zone, biomass, and electron transfer from the reaction center to the quinone pool. Collectively, the results of this study indicate that soil algal bioassays using nonspecific algae can be used to assess soil quality, to derive several toxicity endpoints for individual cells, and to evaluate previously established flow cytometric toxicity endpoints.

Use of titanium dioxide nanoparticles (TiO2 NPs) has become a part of our daily life and the high environmental concentrations predicted to accumulate in aquatic ecosystems are cause for concern. Although TiO2 has only limited reactivity, at the nanoscale level its physico-chemical properties and toxicity are different compared with bulk material. Phytoplankton is a key trophic level in fresh and marine ecosystems, and the toxicity provoked by these nanoparticles can affect the structure and functioning of ecosystems. Two microalgae species, one freshwater (Chlamydomonas reinhardtii) and the other marine (Phaeodactylum tricornutum), have been selected for testing the toxicity of TiO2 in NP and conventional bulk form and, given its photo-catalytic properties, the effect of UV-A was also checked. Growth inhibition, quantum yield reduction, increase of intracellular ROS production, membrane cell damage and production of exo-polymeric substances (EPS) were selected as variables to measure.TiO2 NPs and bulk TiO2 show a relationship between the size of agglomerates and time in freshwater and saltwater, but not in ultrapure water. Under two treatments, UV-A (6 h per day) and no UV-A exposure, NPs triggered stronger cytotoxic responses than bulk material. TiO2 NPs were also associated with greater production of reactive oxygen species and damage to membrane. However, microalgae exposed to TiO2 NPs and bulk TiO2 under UV-A were found to be more sensitive than in the visible light condition. The marine species (P. tricornutum) was more sensitive than the freshwater species, and higher Ti internalization was measured. Exopolymeric substances (EPS) were released from microalgae in the culture media, in the presence of TiO2 in both forms. This may be a possible defense mechanism by these cells, which would enhance processes of homoagglomeration and settling, and thus reduce bioavailability.

Understanding the trophic transfer of nanoparticles (NPs) is important because NPs are small enough to easily penetrate into organisms. In this study, we evaluated the trophic transfer of gold NPs (AuNPs) within the aquatic food chain. We observed AuNPs transfer from 2 species of primary producers (Chlamydomonas reinhardtii or Euglena gracilis) to the primary consumer (Daphnia magna). Also, bioaccumulation of AuNPs in E. gracilis was higher than that in C. reinhardtii. The reasons for the difference in Au accumulation may be the physical structure of these organisms, and the surface area that is available for interaction with NPs. C. reinhardtii has a cell wall that may act as a barrier to the penetration of NPs. The size of E. gracilis is larger than that of C. reinhardtii. This study demonstrates the trophic transfer of AuNPs from a general producer to a consumer in an aquatic environment.

The present study examines the effect of carboxyl-CdSe/ZnS quantum dots (QDs) on Cu and Pb availability to microalgae with different cell wall characteristics: Chlorella kesslerii possessing a cellulosic cell wall and two strains of Chlamydomonas reinhardtii, a wall-less and a walled strain containing glycoproteins as the main cell wall component. Results demonstrated that QDs decreased Pb and Cu intracellular contents ({Cu}ᵢₙₜ and {Pb}ᵢₙₜ) in walled strains by a factor of 2.5 and 2, respectively, as expected by the decrease of about 70% and 40% in the dissolved Cu and Pb concentrations. QDs increased {Cu}ᵢₙₜ and {Pb}ᵢₙₜ in wall-less strain by a factor of 4 and 3.5. These observations were consistent with the observed association of QDs to the wall-less C. reinhardtii, and lack of association to walled algal strains. Suwannee River humic acid did not influence metal association to QDs, but decreased {Cu}ᵢₙₜ and {Pb}ᵢₙₜ in all microalgae.

The wide range of industrial applications of chromium (Cr) has led to an increasing risk of water contamination by Cr(Ⅵ). However, efficient methods to remove or decrease the toxicity of Cr(Ⅵ) in situ are lacking. The main aim of this study was to investigate the mechanisms by which selenite alleviates chromium(Ⅵ)-induced toxicity in Chlamydomonas reinhardtii. Our results showed that K₂Cr₂O₇ had toxic effects on both the structure and physiology of C. reinhardtii in a dose-dependent manner. Adding selenite significantly alleviated chromium accumulation and toxicity in cells. RNA-seq data showed that the expression level of selenoproteins such as SELENOH was significantly increased. Both SELENOH-amiRNA knockdown mutants and selenoh insertional mutant produced more reactive oxygen species (ROS) and grew slower than the wild type, suggesting that SELENOH can reduce chromium toxicity by decreasing the levels of ROS produced by Cr(Ⅵ). We also demonstrated that selenite can reduce the absorption of Cr(Ⅵ) by cells but does not affect the process of Cr(Ⅵ) adsorption and efflux. This information on the molecular mechanism by which selenite alleviates Cr(Ⅵ) toxicity can be used to increase the bioremediation capacity of algae and reduce the human health risks associated with Cr(Ⅵ) toxicity.