Effect of four heavy metals on the biology of Nostoc muscorum

The bundle sheath in Zea mays leaves functions as a protective barrier against the toxic effect of lead

Lead is a highly toxic metal. It impairs the metabolism of living organisms. Plants show different sensitivity to the action of this element. One of the plants with relatively high lead tolerance is Zea mays, where even in detached leaves treated with Pb2+ ions, the photosynthesis rate remains very high compared to other plant species. This study set out to determine the mechanism responsible for the high resistance of maize photosynthetic tissue to the toxic effect of this metal. For this purpose, the cut leaves of Z. mays were incubated in Pb(NO3)2 solutions at different concentrations. Regions of lead accumulation in tissues and cells were located using histochemical methods and transmission electron microscopy. The experiments showed a diverse distribution of lead ions in the leaf blade of Z. mays. Most of the accumulated Pb2+ ions were observed in the vascular bundle and the bundle sheath, while minimal traces of metal were transferred to the mesophyll. In Pisum sativum leaves, although Pb(NO3)2 concentration in the solution was two-fold lower, lead accumulated in all the leaf tissues - mainly in the vascular bundle, epidermis, sclerenchyma, and mesophyll. Thus, bundle sheath cells in maize leaves were able to inhibit the flow of Pb2+ ions to the ground tissue. Therefore, the influence of the toxic metal on photosynthesis in mesophyll cells remained minimal. These experiments show that the structure of Z. mays leaf, with a layer of bundle sheath cells (characteristic of C4 plants), contributes to the protecting photosynthetic tissue against the toxic effect of lead.

Setting a Protective Threshold Value for Silver Toward Freshwater Organisms

Driven by Regulation (EC) No. 1272/2008 and the European Water Framework Directive 2000/60/EC, we have re-evaluated the available chronic freshwater ecotoxicity data for ionic silver (Ag) using strict data quality criteria. In addition, we generated new chronic ecotoxicity data for species potentially sensitive to Ag (the rotifer Brachionus calyciflorus, the cyanobacteria Anabaena flos-aquae, and the aquatic plant Lemna minor) using Ag nitrate as the test substance. The 10% effect concentrations for the most sensitive endpoint per test species were 0.31 µg dissolved Ag/L for B. calyciflorus (population size), 0.41 µg dissolved Ag/L for A. flos-aquae (growth rate), and 1.40 µg dissolved Ag/L for L. minor (root length). We included these values in the set of reliable chronic freshwater data, subsequently covering a total of 12 taxonomic groups and 15 species. Finally, we applied a species sensitivity distribution approach to the data set using various models. The best-fitting model (Rayleigh distribution) resulted in a threshold value protective for 95% of the species of 0.116 µg dissolved Ag/L. This value is considered reliable and conservative in terms of species protection and can be used as a solid basis for setting thresholds for Ag in freshwater after application of an appropriate assessment factor. Furthermore, this value represents reasonable worst-case conditions for bioavailability in European Union surface waters (low hardness and low dissolved organic carbon). Environ Toxicol Chem 2021;40:1678-1693. © 2021 European Precious Metals Federation. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of Silver Nitrate are a Conservative Estimate for the Effects of Silver Nanoparticles on Algae Growth and Daphnia magna Reproduction

Silver (Ag) salts have been shown to be highly toxic to freshwater organisms. There is nevertheless still a high level of uncertainty as to the aquatic effects of Ag nanoparticles (AgNPs), and how these relate to the effects of soluble Ag salts. As part of the substance evaluation for Ag of the European Union Registration, Evaluation, Authorisation, and Restriction of Chemicals regulation, we have generated new data to justify read-across from soluble Ag salts to AgNPs. The aquatic toxicity to algae growth and Daphnia magna reproduction, fate, and behavior of AgNO₃ versus AgNPs were tested and compared. Chloride salts in the test media were replaced with equimolar concentrations of nitrate salts. Total Ag, "conventionally" dissolved Ag (0.45 µm), and "truly" dissolved Ag (3 kDa) were determined. Algae were the most sensitive test species to AgNO₃ (10% effect concentration [EC10] 0.10 µg Ag/L) when expressed as conventionally dissolved Ag. The corresponding value for AgNPs was 0.26 µg/L. For D. magna reproduction, the lowest EC10 values were 3.49 µg Ag/L for AgNO₃ and 33.4 µg Ag/L for AgNPs. Using measured Ag concentrations, AgNO₃ was experimentally shown to be more toxic than AgNPs for all Ag fractions. We explain these observations by a different dissolution behavior of AgNO₃ versus AgNPs. The results provide experimental confirmation that AgNO₃ can be used as a conservative estimate for the aquatic effects of AgNPs at comparable Ag concentrations. Environ Toxicol Chem 2019;38:1701-1713. © 2019 SETAC.

Effects of lead accumulation on the Azolla caroliniana-Anabaena association

The effect of lead accumulation on photopigment production, mineral nutrition, and Anabaena vegetative cell size and heterocyst formation in Azolla caroliniana was investigated. Plants were exposed to 0, 1, 5, 10, and 20 mg L(-1) lead acetate for ten days. Lead accumulation increased when plants were treated with higher lead concentrations. Results revealed a statistically significant decline in total chlorophyll, chlorophyll a, chlorophyll b, and carotenoids in 5, 10, and 20 mg Pb L(-1) treatment groups as compared to plants with 0 or 1 mg Pb L(-1) treatments. No statistically significant change in anthocyanin production was observed. Calcium, magnesium, and zinc concentrations in plants decreased in increasing treatment groups, whereas sodium and potassium concentrations increased. Nitrogen and carbon were also found to decrease in plant tissue. Anabaena vegetative cells decreased in size and heterocyst frequency declined rapidly in a Pb dose-dependent manner. These results indicate that, while A. caroliniana removes lead from aqueous solution, the heavy metal causes physiological and biochemical changes by impairing photosynthesis, changing mineral nutrition, and impeding the growth and formation of heterocysts of the symbiotic cyanobacteria that live within leaf cavities of the fronds.

Pretreatment hepatoprotective effect of the marine fungus derived from sponge on hepatic toxicity induced by heavy metals in rats

The aim of this study was to evaluate the pretreatment hepatoprotective effect of the extract of marine-derived fungus Trichurus spiralis Hasselbr (TS) isolated from Hippospongia communis sponge on hepatotoxicity. Twenty-eight male Sprague-Dawley rats were divided into four groups (n = 7). Group I served as −ve control, group II served as the induced group receiving subcutaneously for seven days 0.25 mg heavy metal mixtures, group III received (i.p.) TS extract of dose 40 mg for seven days, and group IV served as the protected group pretreated with TS extract for seven days as a protection dose, and then treated with the heavy metal-mixture. The main pathological changes within the liver after heavy-metal mixtures administrations marked hepatic damage evidenced by foci of lobular necrosis with neutrophilic infiltration, adjacent to dysplastic hepatocytes. ALT and AST measurements show a significant increase in group II by 46.20% and 45.12%, respectively. Total protein, elevated by about 38.9% in induction group compared to the −ve control group, in contrast to albumin, decreased as a consequence of metal administration with significant elevation on bilirubin level. The results prove that TS extract possesses a hepatoprotective property due to its proven antioxidant and free-radical scavenging properties.

Differential sensitivity of Anabaena doliolum to Cu and Zn in batch and semicontinuous cultures

Elevated concentrations of Cu and Zn inhibited Anabaena doliolum more severely in semicontinuous culture than in batch culture with growth and protein, chlorophyll a, and carotenoid contents generally more than two-fold more sensitive in the former culture system. The greater sensitivity of A. doliolum to test metals in semicontinuous culture was associated with their greater accumulation. The level of inhibition of various parameters of the test organism remained almost constant in semicontinuous culture, but considerable alleviation of the inhibitory effect occurred in batch culture with time concomitant with a regular decline in metal content of cells. However, metal content of cells in semicontinuous culture remained more or less constant with time, thereby causing no change in the level of inhibition. Unlike semicontinuous culture, batch culture showed considerable depletion of phosphate from the medium and a rise in pH (from 7 to 7.8). In conclusion, batch culture is not appropriate for long-term assessment of metal toxicity as it might substantially underestimate toxic effects of heavy metals.