The experiment was performed to evaluate effect of heavy metals on total phytoplankton load (TPL) using water of Turag River adjacent to Ashulia locating on the north-eastern side of Dhaka city, Bangladesh. Total phytoplankton load comprises of Euglena sp., Borodinella sp., Pediastrum biradiatum, Pinnularia sp., Fragillaria sp., Fragillaria crotonensis, Gloeocapsa sp., Navicula sp., Cynedra sp., Crucigenia sp., Chlorella sp., Spirogyra sp., Phacus acuminatus, Phacus circulatus., Nitzschia sp. and Nitzschia clausii. Phytoplankton load showed the abundances Bascillariophyceae (43.75%) > Chlorophyceae (37.50%) > Euglenophyceae (18.75%). The average maximum growth rate (log transformed) of TPL in control culture was -0.25μg/l and treated cultures using 1ppm, 3ppm, 5ppm, 7ppm concentration of heavy metals (Zn and Cu) were 0.03 μg/l, 0.03 μg/l, -0.11 μg/l and -0.26 μg/l, respectively. In treated culture using 1ppm concentration of heavy metals (Zn and Cu) the growth rate of phytoplankton load increased significantly whereas the growth rate decreased at higher concentrations (3ppm, 5ppm and 7ppm) of heavy metals. The implication of this finding can be used to monitor health of riverine ecosystems and management of river pollution.

Studies on Fe uptake by phytoplankton have been often conducted using artificial culture media. However, Fe chemistry in freshwater can be influenced by riverine anthropogenic impacts and other factors causing water quality changes. In this study, therefore, Fe uptake in natural (river and reservoir) and effluent waters was investigated for the notorious bloom-forming freshwater cyanobacterium Microcystis aeruginosa. To investigate the Fe uptake mechanism, a short-term incubational assay was conducted in the presence of light, Fe(II) ligand and Fe(III) reductant, with results consistently indicating that unchelated Fe(III) is the major substrate for Fe uptake by M. aeruginosa. Further assays using various freshwater samples indicated that Fe uptake is lower in natural waters compared to that of effluent waters and, interestingly, Fe uptake was found to be limited in natural waters. These results suggest that Fe limitation can be alleviated by the inflow of effluent waters. Statistical analysis with various water quality variables indicated that Fe availability is significantly influenced by concentrations of dissolved Fe and organic matter as well as specific UV absorbance (an index of aromaticity). Overall, findings of this study highlight that watershed anthropogenic activities exert important roles in Fe uptake by freshwater cyanobacteria via alteration of Fe speciation.

The Deepwater Horizon (DWH) disaster released crude oil in the Gulf of Mexico for 87 days, overlapping with the reproductive season and recruitment of the oyster Crassostrea virginica. The pelagic larval life stages of C. virginica are particularly vulnerable to contaminants such as polycyclic aromatic hydrocarbons (PAHs) and oil droplets. Based on their lipophilic properties, PAHs and oil droplets can adsorb onto phytoplankton and filter-feeding C. virginica larvae may be exposed to these contaminants bound to suspended sediment, adsorbed onto algal and other particles, or in solution. This study examined the effects of exposure of C. virginica larvae to algae mixed with DWH oil. In a 14-day laboratory exposure, 5 day-old C. virginica larvae were exposed to Tisochrysis lutea mixed with four concentrations of unfiltered DWH oil (HEWAF) in a static renewal system. Larval growth, feeding capacity, abnormality and mortality were monitored throughout the exposure. Total PAH (n = 50) content of the water medium, in which larvae were grown, were quantified by GC/MS-SIM. Oil droplets were observed bound to algae, resulting in particles in the size-range of food ingested by oyster larvae (1–30 μm). After 14 days of exposure, larval growth and survival were negatively affected at concentrations of tPAH50 as low as 1.6 μg L⁻¹. GC/MS-SIM analysis of the exposure medium confirmed that certain PAHs were also adsorbed by T. lutea and taken up by oyster larvae via ingestion of oil droplets and/or contaminated algae. Long-term exposure to chronic levels of PAH (1.6–78 μg tPAH50 L⁻¹) was shown to negatively affect larval survival. This study demonstrates that dietary exposure of oyster larvae to DWH oil is a realistic route of crude oil toxicity and may have serious implications on the planktonic community and the food chain.

Applications of aluminium (Al) salt or lanthanum (La) modified bentonite (LMB) have become popular methodologies for immobilizing phosphorus (P) in eutrophic lakes. The presence of humic substances, has been shown to inhibit this form of treatment due to the complexation with La/Al. However, the effects of other dissolved organic matter (DOM), especially that derived from phytoplankton (the dominant source in eutrophic lakes) are unknown. In this study, the interaction with La/Al of Suwannee River Standard Humic Acid Standard II (SRHA) and algae-derived DOM (ADOM) were investigated and compared. Differed to SRHA which was dominated by polyphenol-like component (76.8%, C1-SRHA), majority in ADOM were protein-like substance, including 41.9% tryptophan-like component (C2-ADOM) and 21.0% tyrosine-like component (C3-ADOM). Two reactions of complexation and coprecipitation were observed between SRHA/ADOM and La/Al. Complexation dominated at low metal inputs less than 10 μM and coprecipitation was the main reaction at higher metal inputs. For ADOM, the tryptophan-like component (C2-ADOM) was the important component to react with metal. The reaction rate for C2-ADOM with La were about two-third of that for C1-SRHA, indicating that the influence of C2-ADOM was significant during the P immobilization by La/Al-based treatment in eutrophic lakes. The P removal data in the presence of ADOM confirmed the significant inhibition of ADOM. In addition, based on the composition of coprecipitates and relatively biodegradable character of tryptophan-like substances (C2-ADOM), the coprecipitation of ADOM was assumed to reduce the stability of precipitated P in eutrophic lakes. The release of P from the potential biodegradation of the coprecipitates and thus the possible decline of the performance of P immobilization by La/Al-based treatments is an important work in the future.

Microalgae are commonly used in ecotoxicity testing due to their ease of culturing and rapid cell division rates. These tests generally utilise a single species of algae; however, microalgae occur in the environment as complex communities of multiple species. To date, routine multispecies toxicity tests using tropical microalgae have not been available. This study investigated four tropical freshwater microalgal species for use in a chronic multispecies toxicity test based on the population growth (cell division) rate: Pediastrum duplex, Monoraphidium arcuatum, Nannochloropsis-like sp. and Chlorella sp. 12. Flow cytometric analysis identified the different fluorescence and light scattering properties of each algal species and quantified each species within multispecies mixtures. Following optimisation of test media nutrients and pH, a toxicity testing protocol was developed with P. duplex, M. arcuatum and Nannochloropsis-like sp. There were no significant differences in growth rates of each alga when tested over 72 h as single species or in multispecies mixtures. Atrazine and imazapic, two herbicides with different modes of action, were used to assess the sensitivity of the multispecies toxicity test. Atrazine was toxic to all species with 72-h IC10 values of 7.2, 63 and 280 μg/L for P. duplex, M. arcuatum and Nannochloropsis-like sp. respectively, while imazapic was not toxic to any species at concentrations up to 1100 μg/L. The toxicity of atrazine and imazapic to each microalgal species in the multispecies toxicity test was the same as that determined from single-species toxicity tests indicating that the presence of these microalgae in a mixture did not affect the toxicity of these two herbicides. This study is the first to develop a multispecies tropical microalgal toxicity test for application in freshwaters. This time- and cost-effective tool can be utilised to generate data to assist environmental decision making and to undertake risk assessments of contaminants in tropical freshwater environments.

The influence of trophic status on the distribution of hydrophobic organic contaminants (HOCs) in different subtropical shallow waters at large spatial scales remains largely unknown. In this study, samples of surface sediments, water, total suspended particles, phytoplankton, and zooplankton were simultaneously collected from 83 sampling sites in 20 subtropical oligotrophic to hyper-eutrophic shallow lakes in China to investigate the influence of trophic status on the spatial distribution and sinking fluxes of 16 polycyclic aromatic hydrocarbons (PAHs). The total concentration of the 16 PAHs (ΣPAH₁₆) in the water columns of these lakes varied from 0.22 to 5.81 μg L⁻¹, and increased with the trophic state index (TSI) and phytoplankton biomass. Phytoplankton were the dominant reservoir for the PAHs in the water column. However, the fraction of ΣPAH₁₆ in phytoplankton decreased with the TSI. The average sinking flux of ΣPAH₁₆ of the individual lakes varied from 2257.1 to 261674.1 mg m⁻² d⁻¹, and increased with the TSI of the lakes. The concentration of ΣPAH₁₆ in the surface sediments ranged from 385.77 to 3784.37 ng gdw⁻¹, and increased with the TSI and the ratio of phycocyanin/sediment organic carbon. It suggested that cyanobacterial biomass affected by trophic status dominated the occurrence of the PAHs in the surface sediments of these lakes. Biomass dilution and the biological pump affected the accumulation of the PAHs in phytoplankton, and zooplankton, and had more influence on the PAHs with higher hydrophobicity. Both the bioconcentration factors and bioaccumulation factors of the PAHs decreased with the TSI. No biomagnification was observed for the PAHs from phytoplankton to zooplankton in these lakes in spring. Our study provided novel knowledge for the coupling between eutrophication and HOCs in 20 subtropical shallow lakes with different trophic status.

Cyanobacterial blooms are of global concern due to the multiple harmful risks they pose towards aquatic ecosystem and human health. However, information on the fate of organic pollutants mediated by cyanobacterial blooms in eutrophic water remains elusive. In the present study, endocrine disruptive potentials of phytoplankton samples were evaluated throughout a year-long surveillance in a large and eutrophic freshwater lake. Severe cyanobacterial blooms persisted during our sampling campaigns. Estrogenic agonistic, anti-estrogenic, anti-androgenic, and anti-glucocorticogenic effects were observed in the phytoplankton samples using in vitro reporter gene bioassays. 27 endocrine disrupting chemicals (EDCs) of different modes of action were detected in the samples via UPLC-MS/MS system. Results from mass balance analysis indicated that the measured estrogenic activities were greater than the predicted estrogenic potencies from chemical analysis, demonstrating that chemical analysis of targeted EDCs is unable to fully explain the compounds responsible for the observed estrogenicities. Results from Spearman's correlation analysis concluded that the concentrations of ten EDCs in phytoplankton samples were negatively correlated with cyanobacterial biomass, suggesting the potential occurrence of biomass bio-dilution effects of EDCs due to the huge biomass of cyanobacteria during bloom seasons. The present study provided complementary information about the potential endocrine disruptive risks of cyanobacterial blooms, which is important for understanding and regulating EDCs in eutrophic lakes.

Monitoring diverse components of aquatic ecosystems is vital for elucidation of diversity dynamics and processes, which alter freshwater ecosystems, but such studies are seldom conducted. Phytoplankton and zooplankton are integral components which play indispensable parts in the structure and ecological service function of water bodies. However, few studies were made on how zooplankton and phytoplankton community may respond simultaneously to change of circumstance and their mutual relationship. Therefore, we researched synchronously the phytoplankton communities as well as zooplankton communities based on monthly monitoring data from September 2011 to August 2012 in heavily polluted areas and researched their responses to variation in environmental parameters and their mutual relationship. As indicated by Time-lag analysis (TLA), the long-term dynamics of phytoplankton and zooplankton were undergoing directional variations, what's more, there exists significant seasonal variations of phytoplankton and zooplankton communities as indicated by Non-Metric Multidimensional scaling (NMDS) methods. Also, Redundancy Analysis (RDA) demonstrated that environmental indicators together accounted for 25.6% and 50.1% variance of phytoplankton and zooplankton, respectively, indicating that environmental variations affected significantly on the temporal dynamics of phytoplankton as well as zooplankton communities. What's more, variance partioning suggested that the major environmental factors influencing variation structures of zooplankton communities were water temperature, concentration of nitrogen, revealing the dominating driving mechanism which shaped the communities of zooplankton. It was also found that there was significant synchronization between zooplankton biomass and phytoplankton biomass (expressed as Chl-a concentration), which suggested that zooplankton respond to changes in dynamic structure of phytoplankton community and can initiate a decrease in phytoplankton biomass through grazing in a few months.

Antibiotics have been widely detected in the ocean and have various impacts on the environment, while knowledge of their chronic influence on phytoplankton, especially red tide algae, is still limited. Dinoflagellates and green algae are common phytoplankton in marine ecosystems. The former is the main red tide algae, and the latter is an important primary producer. We investigated the long-term responses of two representative algae, Prorocentrum lima and Chlorella sp., to two common antibiotics (sulfamethoxazole (SMX) and norfloxacin (NFX)) at environmentally relevant levels (10 and 100 ng/L) during simulated natural conditions. The cell density and activities of three antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) were analyzed. The results showed that the influence of each antibiotic on Chlorella sp. was not significant (p > 0.05) during the first 10 days, but the influence of the antibiotics later began to show significant inhibition (p < 0.05) compared with the control group, especially during mixed exposure. P. lima was not inhibited, but its cell density increased. SMX had a superior stimulation effect on P. lima. The three enzymes activities of P. lima increased, and the antioxidant mechanism was not seriously impacted. However, for Chlorella sp., the activity of SOD increased while the activities of CAT and POD decreased, suggesting that this algae’s antioxidant system was unbalanced due to oxidative stress. Based on our results, the growth of P. lima was different from green algae Chlorella sp. as well as other inhibited marine algae (such as diatom, golden algae) studied in previous studies. Therefore, as a typical pollutant in the ocean, antibiotics may play a positive role in the bloom of dinoflagellate red tides.

Nowadays, the occurrence of a large volume of plastic litter in oceanic and coastal zones has increased concern about its impacts on marine organisms. The degradation of plastic polymers leads to the formation of smaller fragments at both micro and nano scale (<5 mm and <1 μm respectively). Nanoplastics (NPs), due to their smaller size and high specific surface area can establish colloidal interactions with marine microalgae, therefore potential toxicity can be led. . To assess this hypothesis, the aim of the present study is to examine the behaviour of polystyrene nanoparticles (PS NPs) of different sizes (50 and 100 nm) in marine water and their possible effects at different physiological and cellular levels in the marine diatom Phaeodactylum tricornutum. Different biomarkers and stress responses in P. tricornutum were analysed when organisms were exposed to environmentally relevant PS NPs concentrations between 0.1 and 50 mg L−1. Our results showed significant differences between controls and exposure microalgae, indicating toxicity. After 24 h, an increase in oxidative stress biomarkers, damage to the photosynthetic apparatus, DNA damage and depolarization of mitochondrial and cell membrane from 5 mg L−1 were observed. Further after 72 h the inhibition of population growth and chlorophyll content were observed. Examining effects the effects related to PS NPs size, the smallest (50 nm) induced greater effects at 24 h while bigger PS NPs (100 nm) at72 h. This bigger particles (100 nm) showed more stability (in size distribution and spherical form) in the different culture media assayed, when compared with the rest of particles used. Strong adsorption and/or internalization of PS NPs was confirmed through changes in cell complexity and cell size as well as the fluorescence of 100 nm fluoresbrite PS NPs after washing cell surface.