Zinc tolerance and zinc removal ability of living and dried biomass of Desmodesmus communis

Metals in Callitriche cophocarpa from small rivers with various levels of pollution in SW Poland

The anthropogenic impact of metals on aquatic environments is a risk for biota, and thus their levels must be controlled. Callitriche cophocarpa Sendtn. belongs to a genus with a potential for accumulation of elevated metal levels. Thus, it may provide consolidated evidence of contamination. Therefore, the aim of this investigation was to determine Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in this species collected together with water and bottom sediments from rivers with various levels of pollution. Of these rivers, one less polluted and one more polluted was selected for the collection of C. cophocarpa for an experiment to compare its Cu and Zn concentration potential. Both metals were supplemented at concentrations 0.01, 0.02, 0.03, 0.05, 0.08 and 0.14 mg L-1 of Cu as CuSO4 × 5H2O and 0.4, 0.6, 0,9, 1,35, 2.03 and 3.04 mg L-1 of Zn as ZnSO4 × 7H2O, and in the binary design containing (mg·L-1) 0.01Cu + 0.4Zn, 0.02Cu + 0.6Zn, 0.03Cu + 0.9Zn, 0.05Cu + 1.4Zn, 0.08Cu + 2.03 Zn and 0.14Cu + 3.04Zn. The upper concentrations of Cr, Cu, Mn and Zn in C. cophocarpa shoots from both types of rivers as well as of Ni and Pb in shoots from more polluted rivers were higher than the values typical for toxicity thresholds with no visible harmful effects, which may indicate accumulation abilities of C. cophocarpa for these metals. Both roots and shoots of C. cophocarpa may be included in the group of macroconcentrators for bottom sediments with respect to Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn and deconcentrators of Pb. Greater accumulation of most metals in roots than in shoots indicates their restricted mobility and translocation by C. cophocarpa to shoots. C. cophocarpa from the less polluted river and exposed to all experimental solutions contained significantly higher levels of Cu and Zn than that from the more polluted river exposed to identical experimental solutions. The plants collected from the more polluted river influenced by surplus of metals and living under chemical stress could probably limit further accumulation by developing a resistance mechanism. Cu and Zn contents in C. cophocarpa were higher when treated with separate metals than for binary treatment both in the more and less polluted river. Such research presenting the impact of a combination of metals could be important for understanding and explaining the interactions of these elements which may influence their bioavailability in nature as well as importance in the evaluation of the risk of environmental toxicity.

Mitigation of zinc toxicity through differential strategies in two species of the cyanobacterium Anabaena isolated from zinc polluted paddy field

The present study describes the physiological and biochemical mechanisms of zinc tolerance in two heterocytous cyanobacteria i.e. Anabaena doliolum and Anabaena oryzae, treated with their respective LC₅₀ concentrations of zinc (3 and 4.5 mg L^-1) for eight days. The feedbacks were examined in terms of growth, metabolism, zinc exclusion, zinc accumulation, oxidative stress, antioxidants and metallothionein contents. Although the growth and metabolic activities were reduced in both the cyanobacterium, maximum adversity was noticed in A. doliolum. The higher order of abnormalities in A. doliolum was attributed to excessive accumulation of zinc and enhanced reactive oxygen species (ROS) production. However, the comparatively higher growth and metabolic activities of A. oryzae were ascribed to the lower accumulation of zinc as a result of released polysaccharides mediated zinc exclusion, synthesis of zinc chelating metallothioneins and subsequent less production of ROS. The oxidative stress and macromolecular damages were prominent in both the cyanobacterium but the condition was much harsher in A. doliolum which may be explained by its comparatively low antioxidative enzyme activities (SOD, APX and GR) and smaller amount of ascorbate-glutathione-tocopherol contents than that of A. oryzae. However, sustenance of 50% growth by A. doliolum under zinc stress despite severe cellular damages was attributed to the enhanced synthesis of phenolics, flavonoids, and proline. Thus, differential zinc tolerance in A. doliolum and A. oryzae is possibly the outcome of their distinct mitigation strategies. Although the two test organisms followed pseudo second order kinetics model during zinc biosorption yet they exhibited differential zinc biosorption capacity. The cyanobacterium A. oryzae was found to be more efficient in removing zinc as compared to A. doliolum and this efficiency makes A. oryzae a promising candidate for the phycoremediation of zinc polluted environments.

Enhanced removal of cesium by potassium-starved microalga, Desmodesmus armatus SCK, under photoheterotrophic condition with magnetic separation

This study investigated the feasibility of using photoheterotrophic microalga, Desmodesmus armatus SCK, for removal of cesium (Cs⁺) followed by recovery process using magnetic nanoparticles. The comparison of three microalgae results indicated that D. armatus SCK removed the most Cs⁺ at both 25 °C and 10 °C. The results also revealed that the use of microalga grown in potassium (K⁺)-starved condition improves the accumulation of Cs⁺. Heterotrophic mode with addition of volatile fatty acids (VFAs), especially acetic acids (HAc), also enhanced removal of Cs⁺ by K⁺-starved D. armatus SCK; maximum removal efficiency of Cs⁺ was almost 2-fold higher than that of cells grown without organic carbon source. The Cs⁺ taken up by this microalga was efficiently harvested using magnetic nanoparticles, polydiallyldimethylammonium (PDDA)-FeO₃. Finally, this strain eliminated more than 99% of radioactive ¹³⁷Cs from solutions of 10, 100, and 1000 Bq mL^-1. Therefore, use of K⁺-starved microalga, D. armatus SCK, with VFAs could be promising means to remove the Cs from the liquid wastes.

The Role of Planktonic Algae in the Ecological Assessment of Storage-Reservoirs of the ILI-Balkhash Basin

The largest wastewater treatment systems include Sorbulak and Kurty reservoirs, and the small storage ponds were studied in the summer of 2017 and characterized mainly by organic pollution. Phytoplankton communities were represented by species tolerant of organic and toxic pollution. Cyanobacteria dominated in the reservoirs, and dinophyte algae were only in the Kurty Reservoir. According to the results of CCA analysis, only Cr and certain nutrients had a significant effect on the abundance of algae. A statistically positive significant association between the Shannon index and the average algal cell mass was established. The results obtained are a particular example reflecting the non-linearity of changes in plankton communities in the gradient of nutrient loading and eutrophication of aquatic ecosystems.

Zinc-induced differential oxidative stress and antioxidant responses in Chlorella sorokiniana and Scenedesmus acuminatus

Algae are frequently exposed to toxic metals, and zinc (Zn) is one of the major toxicants present. We exposed two green microalgae, Chlorella sorokiniana and Scenedesmus acuminatus, to sub-lethal concentrations (1.0 and 0.6mM) of Zn for seven days. Algal responses were analysed at the level of growth, oxidative stress, and antioxidants. Growth parameters such as cell culture yield and pigment content were less affected by Zn in C. sorokiniana, despite the fact that this alga accumulated more zinc than S. acuminatus. Also, C. sorokiniana, but not S. acuminatus, was able to acclimatize during long-term exposure to toxic concentrations of the test metals (specific growth rate (µ) was 0.041/day and total chlorophyll was 14.6mg/mL). Although, Zn induced oxidative stress in both species, C. sorokiniana experienced less stress than S. acuminatus. This could be explained by a higher accumulation of antioxidants in C. sorokiniana, where flavonoids, polyphenols, tocopherols, glutathione (GSH) and ascorbate (ASC) content increased. Moreover, antioxidant enzymes glutathione S transferase (GST), glutathione reductase (GR), superoxide dismutase (SOD), peroxidase (POX) and ascorbate peroxidase (APX), showed increased activities in C. sorokiniana. In addition to, and probably also underlying, the higher Zn tolerance in C. sorokiniana, this alga also showed higher Zn biosorption capacity. Use of C. sorokiniana as a bio-remediator, could be considered.