Enhancing the phosphorus content of layered double hydroxide fertilizers by intercalating polymeric phosphate instead of orthophosphate: A feasibility study.

HYPOTHESIS: Layered double hydroxide (LDH) loaded with orthophosphate (PO4) are suggested as slow-release P fertilizers. However, PO4-LDHs have a low maximal P content, related to high charge HPO42-/PO43- anions occupying the anion exchange capacity (AEC) of LDHs. We postulate that the P content of LDHs can be enhanced by exchanging them with polymeric-P (i.e. trimetaphosphate, P3O9), which has a lower molar charge/P ratio than its monomer. EXPERIMENTS: Adsorption capacities were compared between PO4 and P3O9 for as-synthesized and calcined MgAl LDHs with Mg/Al ratio of 2, 3, or 4; the P-LDHs were characterized (XRD, FTIR). Dialysis and soil incubation experiments were performed with PO4-LDHs, P3O9-LDHs, and corresponding soluble fertilizers to compare their P release and P solubility (CaCl2 extract). FINDINGS: The P adsorption capacities were 1.25-1.60 fold larger for P3O9 compared to PO4, yet the high theoretical P contents with P3O9 were not achieved (incomplete loading, P3O9 depolymerization). P3O9-Mg3Al released polymeric-P whereas P3O9-Mg2Al released depolymerized PO4, and P release from P3O9-LDHs was slower than that of PO4-LDHs. With soil incubation, soluble P from P3O9-LDH was initially lower but later converged to that of PO4-LDH as result of continued hydrolysis, yet did not exceed that of the soluble P3O9 and PO4 fertilizers.

Layered Double Hydroxides as Slow-Release Fertilizer Compounds for the Micronutrient Molybdenum.

Molybdenum (Mo) is an essential plant micronutrient. Despite low plant Mo requirements, deficiencies are not uncommon and soluble Mo fertilizers are often applied. However, soluble Mo may result in poor Mo use efficiency due to strong sorption (acid weathered soils) or leaching (lighter-textured soils). Here, ZnAl layered double hydroxides (LDHs), loaded with molybdate (MoO4), were examined for their potential as slow-release Mo compounds. Chloride-exchanged LDHs with varying Zn/Al ratios (2, 3, and 4) were exchanged with MoO4. Zn2Al LDH indicated MoO4 intercalation, whereas Zn3Al and Zn4Al LDHs bound MoO4 merely on edge sites. Short-term Mo-LDH incubation identified sulfate, carbonate, and phosphate as the most competitive anions for MoO4 exchange. Long-term Mo-LDH incubation in simulated pH-neutral soil solutions demonstrated slow Mo release from Zn2Al LDH (half-life of 35 h), with a total Mo desorption of up to 85%. For Zn3Al and Zn4Al LDHs, Mo desorption was limited to <20%. Finally, several macronutrient fertilizers were tested as possible carriers for Mo-LDH fertilizer compounds.

Addressing challenges in providing a reliable ecotoxicology data for graphene-oxide (GO) using an algae (Raphidocelis subcapitata), and the trophic transfer consequence of GO-algae aggregates.

The graphene oxide (GO) due to its exceptional structure, physicochemical and mechanical properties is a very attractive material for industry application. Even though, the unique properties of GO (e.g. structure, size, shape, etc.) make the risk assessment of this nanomaterial very challenging in comparison with conventional ecotoxicology studies required by regulators. Thus, there is a need for standardized characterization techniques and methodology to secure a high quality/reliable data on the ecotoxicology of GO, and to establish environmentally acceptable levels. Herein, authors address the crucial quality criteria when evaluating the ecotoxicology of GO using an algae (Raphidocelis subcapitata) and a shrimp (Paratya australiensis). This study provides a detail characterization and modification of the used GO, robust quantification and a suspension stability in different media for ecotoxicology studies. It was observed that under the same exposure conditions the behavior of GO and the estimated outcomes (IC50 values) in modified algae media differed in comparison to the referent media. Further to that, the adverse effects of GO on the algae cell structure and the potential uptake of GO by the algae cells were examined using the TEM with different staining techniques to avoid artefacts. Shrimps which were exposed to GO-algae aggregates via the food intake did not indicate stress or accumulation of GO. Our work presents an important insight to necessity of establishing a benchmark ecotoxicology assays for GO (e.g. characterization techniques, choice of media, etc.) and providing a reliable data to be used by regulators in risk assessment of two-dimensional (2D) nanomaterials.

Pollution and Health Risk Assessments of Potentially Toxic Elements in Soil and Sediment Samples in a Petrochemical Industry and Surrounding Area.

The pollution state and health risk assessment of potentially toxic elements (PTE) in soil and sediment samples of the petrochemical industry and its surrounding area are evaluated in this study. The pseudo-total contents of Ba, Cd, Co, Cu, Cr, Mn, Ni, Pb, V, Zn, As, Hg, and Se were measured by inductively coupled plasma-optical emission spectrometry (ICP/OES) in analyzed samples. Instead of determining total content, we performed aqua regia of the samples. The silicate matrix remained, and the quantities of elements that are within the silicate matrix do not represent an environmental danger. The soils from the chlor-alkali plant are highly polluted by Hg (the enrichment factor values were above 6000), and by Cu, Cd, Pb, and Zn, while the sediment samples from the wastewater channel are polluted with Cr, Cd, and Hg. The measured element contents are used for calculating health risk criteria for a composite worker (a worker who is exposed, long-term, during the work day) and for residential people. Hg is the element that mainly contributes to non-carcinogenic risks within the petrochemical area. The highest value of total carcinogenic risk obtained in the sediment sample from the wastewater channel, and the metal that mostly contributes is Cr. The areas closest to the petrochemical industry have higher values of health risk criteria parameters and pollution indices. The areas that are located further to the north and south from the petrochemical industry are less burdened with the analyzed elements, which is significant because the closest city and village are situated in those directions.

Microbial levan and pullulan as potential protective agents for reducing adverse effects of copper on Daphnia magna and Vibrio fischeri.

Microbial polysaccharides, due to their unique physiochemical properties, have found application in the food industry, cosmetics, pharmacy and medicine. In the environment, microbes can use polysaccharides to alleviate the adverse effects of heavy metals in their close proximity. This adaptive property shows interesting potential for bioremediation. Herein, the effects of the exopolysaccharides (EPS) levan, produced by the bacterium Bacillus licheniformis NS032 and pullulan, produced by the fungus Aureobasidium pullulans CH-1 in the presence of copper (Cu2+) have been investigated for the first time on antioxidant enzyme activity, respiration and Cu2+ bioaccumulation of Daphnia magna as well as the bioluminescence of Vibrio fischeri. Both EPS decreased toxicity of Cu2+ in the acute test with D. magna. The activity of catalase (CAT) was significantly diminished after acute exposure to Cu2+ in comparison to treatments with Cu2+ and EPS, while in the prolonged acute exposure the CAT activity did not show statistically significant (P ≤ 0.05) differences between treatments with and without the EPS. According to ICP-MS results, during prolonged acute exposure of neonates, the bioaccumulation of Cu2+ in treatments without the EPS was 52.03 µg/g of biomass (wet), while in treatments with EPS, the bioaccumulation was lower by one order of magnitude. The respiration of neonates during acute exposure to Cu2+ with or without the EPS was monitored using the MicroOxymax respirometer, and the results show the EPS can positively effect the respiration. In the case of bacterial bioluminescence, the toxicity of Cu2+ decreased in treatments with EPS (30 min EC10) from 3.54 mg/L to 140.61 mg/L (levan) and 45.00 mg/L (pullulan). This study demonstrates protective effect of EPS against Cu2+ toxicity on D. magna and V. fischeri, and opens the door for further investigation of potential application of levan and pullulan in bioremediation of heavy metals and mitigation of their adverse effects in the aquatic environment.

Size-segregated trace elements in continental suburban aerosols: seasonal variation and estimation of local, regional, and remote emission sources.

We have measured trace element contents in suburban aerosols from six size fractions in the range of PM0.27-16 from a background station in Belgrade (Serbia). The distribution and concentration of elements were determined within each of the investigated Dp fractions with emphasis on the fine and coarse modes. Fine/coarse mode ratios of element can provide information regarding their anthropogenic or natural origin. Analysis of seasonal variations of element contents in fine and coarse mode show that Cd, Co, K, and V have higher concentrations in the fine mode during heating season, while Fe contents are lower. In the coarse mode, Cu and V have higher concentrations during the heating season, while Al, Fe, Mg, Mn, and Sb contents are lower. We also apply a distribution probability model (normal, log-normal, and three-parameter Weibull) as new approach to estimate the distances of emission sources that can contribute to pollutant contents in particulate matter of the investigated location.

Partitioning of particulate matter and elements of suburban continental aerosols between fine and coarse modes.

The results presented in this work demonstrate for the first time a distribution of elements in the spectral analysis of aerosols in the suburban continental Balkan Peninsula. Samples were collected in the suburban area of Belgrade (Serbia) in the period from March 2012 till December 2013. Results presented here are from long-term measurements of masses of size-segregated aerosols and macro- and microelements in the range of PM0.27-16. The following elements were analyzed: Al, Ag, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Ti, Tl, V, and Zn; levels of Be, Hg, and Se were under the detection limits in all samples. Average concentrations and time and seasonal variations of particulate matter (PM) as well as element contents and their percentage shares are given. The results showed the domination of particle content around the accumulation mode in the range of 0.53 < Dp < 1.06 µm, but the fractional distribution of elements showed maximal average concentrations in different fractions depending on the origin of each element. Crustal elements (Al, Ca, Fe, Mg, Mn, Ti, etc.) dominated in coarse mode, while anthropogenic elements (As, Cd, Cu, Pb, Sb, etc.) were mainly distributed in fine mode fractions. Some elements, such are As and Ni, were detected in investigated aerosols only occasionally, while others, such as Ca, Fe, and Mg, were detected in all analyzed samples. The application of multivariate analysis (PCA) demonstrated the connection between the elements of similar origin, in fine fractions mainly of anthropogenic origin, while in coarse mode of crustal origin, indicating the resuspension with contribution of about 40%. The contents of some measured elements were compared with their contents in aerosols in some European suburban areas.

Aquatic sediments pollution estimate using the metal fractionation, secondary phase enrichment factor calculation, and used statistical methods.

The sequential extraction procedure of the European Community Bureau of Reference (BCR) was applied for the fractionation of Cd, Cr, Cu, Ni, Pb, Zn, Fe, Mn, and V in the Serbian river sediments. The aim of this paper was to describe a new approach in detection of anthropogenic elements in sediments, related to the Serbian river courses in order to assess their metal contamination. For sediment pollution evaluation, the risk assessment code (RAC) and the secondary phase enrichment factor (KSPEF) were used. Metal fractionation showed more easily mobilized forms predominant for copper, zinc, cadmium, manganese, and lead, which can be one of the indicators for anthropogenic source input. Chromium, nickel, iron, and vanadium found in the residual fraction indicate these metals may be an indicator for natural sources input. Based on RAC classification, results of sediments show no risk (Cr and V), low risk (Ni, Pb, and Fe), medium risk (Cu), high risk (Cd and Zn), and very high risk (Mn). The mean values of KSPEF were Cd > Cu > Zn > Ni > Mn > Pb > Fe > Cr > V, decreasing scale of no to moderately severe enrichment. The sediments were found to be contaminated by heavy metals to various extents, mostly Cd, Cu, and Zn. Research has shown the importance of KSPEF in quantifying degree of metal enrichment in sediments using results of sequential extraction. With the application of this factor, which is not frequently used in the scientific literature, the results obtained with sequential extraction can be used not only for assessment of mobility but also to quantify the metal pollution.

Evaluation of sediment contamination with heavy metals: the importance of determining appropriate background content and suitable element for normalization.

In the present study, concentrations of heavy metals (Cd, Cu, Co, Mn, Cr, Ni, Pb, and Zn) were determined at 35 river sediments in Serbia. The anthropogenic heavy metals input and quantification of the metal enrichment degree in sediments were estimated by calculating geo-accumulation indices (I(geo)) and enrichment factors (EF). These pollution indices have been calculated using different background values (continental crust and local background values) and different element used for normalization (Al and Fe), followed by result comparison. The EF values calculated with continental crust as background (minor to extremely severe enrichment) were higher than when regional background values were used (minor to moderate enrichment). Significant influence of background values on the I(geo) values is observed. Values of geo-accumulation index (<2) revealed that studied river sediments are remaining unpolluted to moderately polluted with Co, Mn, Cr, and Ni. Significant pollution in the sediments was observed for Cd, Cu, Pb, and Zn elements. The results of this study confirm the relevance of precise and accurate determining of local background concentrations while assessing sediment pollution. The values of EFs for studied elements were more influenced by the choice of background values than selection of element used for normalization. Our recommendation would be to use the local and regional background content in quantification of metal contamination in sediments, since these values differ and are site and region dependent.

Conventional, microwave, and ultrasound sequential extractions for the fractionation of metals in sediments within the Petrochemical Industry, Serbia.

In this paper, the main objective was fractionation of Cd, Cu, Ni, Pb, Zn, Ca, Fe, and K in certificate material and sediment samples gathered from and around the Petrochemical Industry using the conventional, microwave and ultrasonic sequential extraction. Microwave oven and ultrasound bath were used as an energy source for achieving faster extraction. Additional heating and boiling of samples were avoided by using lower power and shorter time for microwave and ultrasound extraction. Precision and accuracy of procedure were evaluated by using certificate material (BCR701). Acceptable accuracy of metals (87.0-111.3 %) was achieved for all three-step sequential of conventional extraction protocol. An accuracy of the fourth step has been verified with two certificate materials: BCR143R and 146R. The range of total extracted metal concentrations from sediments was similar for all three extraction techniques. A significant high percentage of Cd, Cu, and Zn were obtained after extraction of the exchangeable and acid soluble sediment fraction. Principal component analysis of values obtained after determination of risk assessment code using conventional and ultrasound sequential extraction show similarity of these values. Accuracy, recovery, and risk assessment code values imply that ultrasound sequential extraction is a more suitable, accelerated sequential extraction procedure (30 min per extraction step) than microwave extraction in applied conditions.

Aqua regia extracted metals in sediments from the industrial area and surroundings of Pancevo, Serbia.

Surface and buried sediments were analyzed for Ba, Ca, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn and V, as well as for total carbon and hydrogen to assess the distribution of sediment pollution due to the vicinity of the petrochemical complex. The samples, collected from 20 locations within the petrochemical complex and from 16 locations outside the complex, were aqua regia extracted and analyzed by ICP/OES. Metals were determined with an acceptable accuracy for certified metals of 82-113%. The precision for the aqua regia extraction was satisfactory, less than 20%, except for Cd where it was 28%. Comparison of the data from the petrochemical with those from the non-petrochemical areas showed different distributions of the metals. Metals that exceeded the baseline range; Ba, Cd, Cu, Zn and Pb, were detected in higher concentrations in sediments that were under the influence of the chlor-alkali plant within the petrochemical complex. Comparison with data from the petrochemical complex and its surroundings and their distribution demonstrated that the metal compositions of the sediments were modified by anthropogenic activities.