Incubation
Incubation was carried out in an aquatic medium with added metals for 90 min at 24 °C. The multi-element solution for the incubation was prepared using double-distilled water and the following certified reference samples: zinc (state standard reference sample No. 7770-2010, concentration of 1 mg/mL in 1 M hydrochloric acid), cadmium (state standard reference sample No. 7773-2008), copper (state standard reference sample No. 8210-2008), and lead (state standard reference sample No. 778-2008, concentration of 1 mg/dm3 in 1 M nitric acid).
Sodium hydrogen carbonate was used to neutralise the excess acidity, resulting in a final solution pH of 2.4.
The calculated concentrations of metals in the solution are as follows, in mg/L: Cu — 2; Pb — 0.1; Zn — 2; Cd — 0.1.
The resulting solution was analysed by mass spectrometry with inductively coupled plasma (ICP-MS). The analytical results were as follows, in ppm: Cu — 1.854; Pb — 0.102; Zn — 2.174; Cd — 0.092.
The metal concentrations were chosen based on the relative degree of toxicity of metals and the possible presence of these metals in the polluted water of aquatic ecosystems.
Sample Preparation and Measurement
The experiment yielded 4 biomass samples, which were dried to a constant weight at 80 °C in a drying oven. After that, they were ashed with 2 drops of concentrated nitric acid, first on a hot plate, and then in a muffle at 450 °C for 2 h. Table 1 presents sample descriptions and the weight of the dry matter and ash.
Table 1. Characteristics of the analysed samples.
Sample Dry weight, g Ash weight, g Ash content, % Sample 1 — biomass after incubation 0.6265 0.0493 7.9 Sample 2 — biomass without incubation 0.6590 0.054 8.2 Sample 3 — dead biomass (mortmass) after incubation 0.3962 0.0201 5.1 Sample 4 — dead biomass (mortmass) without incubation 0.5276 0.0249 4.7
Ash of solid samples was dissolved by acid leaching (concentrated HCl, concentrated HNO3 and 1:1 H2SO4). After decomposition, the samples were transferred into sterile centrifugal volumetric tubes and brought to the appropriate volume with double-distilled water (2.7 μS/cm).
Mortmass. Samples were obtained by drying the biomass at 90 °C for 4 h, before which the samples were stored in a freezer at − 15 °C for 1.5 months. Dried samples were in the form of a dark brown vitrified mass. The mass was ground into a powder with a pestle in a porcelain mortar prior to incubation.
The stripping voltammetry method was previously described (Ostroumov and Shestakova, 2009). The concentration of copper in prepared solutions was determined after the decomposition of biomass by the stripping voltammetry method using the AKV — 07 MK analyzer (OOO “Akvilon”, Russia) with a three-electrode sensor (rotating measuring carbositall electrode AKU-1, auxiliary electrode and reference electrode). Measurements of copper and lead were performed according to the copper programme at an accumulation potential of − 0.9 V against 0.05 M HCl and 1 · 10− 4 M Hg(NO3)2. Automated measurements and results processing were carried out in the “Polar-4.1” programme. The detection limit is 2 ppb (μg/l), and the convergence (relative root-mean-square standard deviation) is 10%. This method allows for the detection of electrochemically active forms of copper that can be reduced to metal under these conditions to form the amalgam.
IncubationIncubation was carried out in an aquatic medium with added metals for 90 min at 24 °C. The multi-element solution for the incubation was prepared using double-distilled water and the following certified reference samples: zinc (state standard reference sample No. 7770-2010, concentration of 1 mg/mL in 1 M hydrochloric acid), cadmium (state standard reference sample No. 7773-2008), copper (state standard reference sample No. 8210-2008), and lead (state standard reference sample No. 778-2008, concentration of 1 mg/dm3 in 1 M nitric acid).Sodium hydrogen carbonate was used to neutralise the excess acidity, resulting in a final solution pH of 2.4.The calculated concentrations of metals in the solution are as follows, in mg/L: Cu — 2; Pb — 0.1; Zn — 2; Cd — 0.1.The resulting solution was analysed by mass spectrometry with inductively coupled plasma (ICP-MS). The analytical results were as follows, in ppm: Cu — 1.854; Pb — 0.102; Zn — 2.174; Cd — 0.092.The metal concentrations were chosen based on the relative degree of toxicity of metals and the possible presence of these metals in the polluted water of aquatic ecosystems.Sample Preparation and MeasurementThe experiment yielded 4 biomass samples, which were dried to a constant weight at 80 °C in a drying oven. After that, they were ashed with 2 drops of concentrated nitric acid, first on a hot plate, and then in a muffle at 450 °C for 2 h. Table 1 presents sample descriptions and the weight of the dry matter and ash.Table 1. Characteristics of the analysed samples.Sample Dry weight, g Ash weight, g Ash content, % Sample 1 — biomass after incubation 0.6265 0.0493 7.9 Sample 2 — biomass without incubation 0.6590 0.054 8.2 Sample 3 — dead biomass (mortmass) after incubation 0.3962 0.0201 5.1 Sample 4 — dead biomass (mortmass) without incubation 0.5276 0.0249 4.7 Ash of solid samples was dissolved by acid leaching (concentrated HCl, concentrated HNO3 and 1:1 H2SO4). After decomposition, the samples were transferred into sterile centrifugal volumetric tubes and brought to the appropriate volume with double-distilled water (2.7 μS/cm).Mortmass. Samples were obtained by drying the biomass at 90 °C for 4 h, before which the samples were stored in a freezer at − 15 °C for 1.5 months. Dried samples were in the form of a dark brown vitrified mass. The mass was ground into a powder with a pestle in a porcelain mortar prior to incubation.The stripping voltammetry method was previously described (Ostroumov and Shestakova, 2009). The concentration of copper in prepared solutions was determined after the decomposition of biomass by the stripping voltammetry method using the AKV — 07 MK analyzer (OOO “Akvilon”, Russia) with a three-electrode sensor (rotating measuring carbositall electrode AKU-1, auxiliary electrode and reference electrode). Measurements of copper and lead were performed according to the copper programme at an accumulation potential of − 0.9 V against 0.05 M HCl and 1 · 10− 4 M Hg(NO3)2. Automated measurements and results processing were carried out in the “Polar-4.1” programme. The detection limit is 2 ppb (μg/l), and the convergence (relative root-mean-square standard deviation) is 10%. This method allows for the detection of electrochemically active forms of copper that can be reduced to metal under these conditions to form the amalgam.
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