Effects of increasing concentrations of unamended and gypsum modified bauxite residues on soil microbial community functions and structure - A mesocosm study.

Bauxite residues (BR), commonly named red muds, are the saline-sodic waste produced during the extraction of alumina from bauxite. In this study, four kinds of BR were mixed at increasing concentrations with two soils in a mesososm experiment. Unamended BR from Provence (PRO) and Guinea (GUI) bauxite were selected, and Modified Bauxite Residues from PRO and GUI (MBR-PRO and MBR-GUI) were obtained by gypsum application and repeated leaching, in order to reduce their pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP). Several indicators of microbial community functions and structure (growth of culturable bacteria; enzymatic activities; C-sourced substrates degradation (Biolog®); bacteria and fungi PCR-RFLP fingerprints) were measured after 35 days of incubation. Results showed that PRO residue had stronger negative effects than GUI on all the tested indicators. Residues modified by gypsum addition (MBR-PRO, MBR-GUI) were equally or sometimes less harmful compared to unamended residues. Microbial activities (bacterial growth and enzyme activities) were more inhibited than the diversity of microbial functions (Biolog®), and the structure of bacterial and fungal communities was not affected by increasing concentrations of bauxite residues. EC and ESP were the main factors explaining the inhibition of microbial activities, although the origin of bauxite residue is of great importance too.

Setal-epidermal, muscular and enzymatic anomalies induced by certain agrochemicals in the earthworm Eudrilus eugeniae (Kinberg).

Eudrilus eugeniae, the vermicomposing worm, is found in considerable numbers in agricultural fields in India due to their eventual transfer through vermimanure. These worms are very often exposed to pesticides, herbicides, chemical fertilisers and other soil amendments. This paper reports the effects of variable concentrations of urea, phosphogypsum (PG), paper mill sludge (PMS) and two organophosphorus agrochemicals, monocrotophos and glyphosate, on certain morphological, histological and biochemical parameters of E. eugeniae. Results indicated setal anomalies, epidermal lesions, clitellar swelling and constriction of the body. Disintegration of connective tissue, vacuolation of dermis and significant alterations in protein, lipid peroxidation levels and activities of lactate dehydrogenase, acetylcholinesterase and catalase have also been observed in the treated worms. It is proposed that setae, connective tissue, protein and enzymes in E. eugeniae could be useful markers to evaluate toxicity due to the test chemicals.

Histological anomalies and alterations in enzyme activities of the earthworm Glyphidrillus tuberosus exposed to high concentrations of phosphogypsum.

Phosphogypsum (PG) is the major solid waste generated by phosphate fertilizer plants and is used worldwide as sulfur and calcium supplement in agricultural soil. Considering the probability of elevated doses of PG during agricultural applications, this study was carried out to assess its impact on the connective tissue, tissue cholinesterase (ChE) activity, lactate dehydrogenase (LDH) activity, and lipid peroxidation (LPX) level of the tropical earthworm Glyphidrillus tuberosus (Stephenson) found in abundance in the rice fields in India. Consistent loss of connective tissue and sloughing of the intestinal epithelium were observed in worms exposed to 10%, 15%, and 20% concentrations of PG in soil over an incubation period of 30 days. ChE, LDH activities, and the level of LPX indicated highly significant variation (p < 0.01) between pre and postclitellar regions of the worm and concentrations of treatment. ChE activity was higher in postclitellar with respect to preclitellar region; however, the values for LDH activity and LPX level were higher in preclitellar region in comparison to postclitellar region in both PG treated and control worms. It was concluded that PG concentration at and beyond 10% could cause damage to muscle fibers and bring about significant alterations in these enzyme activities in G.tuberosus thus affecting the physiology and ecological functions of these worms.

Phosphogypsum as a soil fertilizer: Ecotoxicity of amended soil and elutriates to bacteria, invertebrates, algae and plants.

Phosphogypsum (PG) is a metal and radionuclide rich-waste produced by the phosphate ore industry, which has been used as soil fertilizer in many parts of the world for several decades. The positive effects of PG in ameliorating some soil properties and increasing crop yields are well documented. More recently concerns are emerging related with the increase of metal/radionuclide residues on soils and crops. However, few studies have focused on the impact of PG applications on soil biota, as well as the contribution to soils with elements in mobile fractions of PG which may affect freshwater species as well. In this context the main aim of this study was to assess the ecotoxicity of soils amended with different percentages of Tunisian phosphogypsum (0.0, 4.9, 7.4, 11.1, 16.6 and 25%) and of elutriates obtained from PG - amended soil (0.0, 6.25, 12.5 and 25% of PG) to a battery of terrestrial (Eisenia andrei, Enchytraeus crypticus, Folsomia candida, Hypoaspis aculeifer, Zea mays, Lactuca sativa) and aquatic species (Vibrio fischeri, Daphnia magna, Raphidocelis subcapitata, Lemna minor). Both for amended soils and elutriates, invertebrates (especially D. magna and E. andrei) were the most sensitive species, displaying acute (immobilization) and chronic (reproduction inhibition) effects, respectively. Despite the presence of some concerning metals in PG and elutriates (e.g., zinc and cadmium), the extremely high levels of calcium found in both test mediums, suggest that this element was the mainly responsible for the ecotoxicological effects observed. Terrestrial and aquatic plants were the most tolerant species, which is in line with studies supporting the application of PG to increase crop yields. Nevertheless, no stimulatory effects on growth were observed for any of the species tested despite the high levels of phosphorus added to soils by PG. Given the importance of soil invertebrates for several soil functions and services, this study gives rise to new serious concerns about the consequences of PG applications on agricultural soils.

Health risk assessment of heavy metals contamination in tomato and green pepper plants grown in soils amended with phosphogypsum waste materials.

Phosphogypsum (PG) is a waste produced by the phosphate fertilizer industry that has relatively high concentrations of some heavy metals (e.g., Cd, Cr, Cu, Pb, V, and Zn). The present study was conducted to investigate heavy metal contamination in soils and vegetables (tomatoes and green peppers) and to evaluate the possible health risks associated with the consumption of vegetables grown in PG-amended soils. The enrichment factor values indicated that Pb, Cr, Cu, Ni, Zn, and V were depleted to minimally enriched, and Cd was moderately enriched. The pollution load index values indicated that the PG-amended soils were strongly polluted with Cd, moderately polluted with Cr and Ni, and slightly polluted with Pb, Cu, Zn and V. The geo-accumulation index values indicated that the PG-amended soils were uncontaminated with Pb, Cr, Cu, Ni, Zn, V, and moderately contaminated with Cd. The trace metal transfer for Cd, Cr, Pb, and Zn concentrations was below what are considered as acceptable limits (<1) for food production in soil and vegetables (tomatoes and green peppers) at each site area. Soil-to-plant transfer factor values decreased in order of Zn > Pb > Cd > Cr. The biological absorption coefficients in plants are, in order of highest to lowest, Pb > Zn > Cd > Cr, which suggests that Pb is more bioavailable to plants than Cd, Cr, and Zn. Furthermore, this study highlights that both adults and children consuming vegetables (e.g., tomatoes and green peppers) grown in PG-amended soils ingest significant amounts of the metals studied. However, the daily intake of metals (DIM) and the health risk index (HRI) values are <1, indicating a relative absence of health risks associated with the consumption of vegetables/fruits grown in PG-amended soils. However, while DIM and HRI values suggest that the consumption of plants grown in PG-amended soils is nearly free of risks, there are other sources of metal exposures such as dust inhalation, dermal contact, and ingestion (for children) of metal-contaminated soils, which were not included in this study.

Development of calcium phosphate/sulfate biphasic cement for vital pulp therapy.

OBJECTIVES: Bioactive calcium phosphate cement (CPC) has been used widely to repair bone defects because of its excellent biocompatibility and bioactivity. However, the poor handling properties, low initial mechanical strength, and long setting time of CPC limit its application in vital pulp therapy (VPT). The aim of this study was to synthesize biphasic calcium phosphate/sulfate cements and evaluate the feasibility of applying these cements in VPT. METHODS: The physical, chemical, and mechanical properties of CPC were improved by mixing the cement with various amounts of α-calcium sulfate hemihydrate (CSH). The hydration products and crystalline phases of the materials were characterized using scanning electron microscopy and X-ray diffraction analysis. In addition, the physical properties, such as the setting time, compressive strength, viscosity, and pH were determined. Water-soluble tetrazolium salt-1 and lactase dehydrogenase were used to evaluate cell viability and cytotoxicity. RESULTS: The developed CPC (CPC/CSH cement), which contains 50wt% CSH cement, exhibited no obvious temperature increase or pH change during setting when it was used as a paste. The initial setting time of the CPC/CSH biphasic cement was substantially shorter than that of CPC, and the initial mechanical strength was 23.7±5.6MPa. The CPC/CSH cement exhibited higher viscosity than CPC and, thus, featured acceptable handling properties. X-ray diffraction analysis revealed that the relative peak intensity for hydroxyapatite increased, and the intensity for calcium sulfate dehydrate decreased as the amount of CPC was increased. The cell viability and cytotoxicity test results indicated that the CPC/CSH cement did not harm dental pulp cells. SIGNIFICANCE: The developed CPC/CSH biphasic cement exhibits substantial potential for application in VPT.

[Experimental studies on the effect of the dust of phosphogypsum and its derivatives]. / Eksperimental'nye issledovaniia deistviia na organizm pyli fosfogipsa i produktov ego pererabotki.

The acute toxicity of phosphogypsum and its derivatives was studied. The agents were found to be low and moderate toxic.

[Working conditions and health-related measures in the processing of waste products of phosphorus-containing mineral fertilizers]. / Usloviia truda i ozdorovitel'nye meropriiatiia v proizvodstve po pererabotke otkhodov polucheniia fosforsoderzhashchikh mineral'nykh udobrenii.

In the processing of the waste products of phosphorus containing fertilizer production, several major health-related factors were identified depending on the industrial site's peculiarities: unfavourable microclimate conditions (both cold and heat), relative temperature differences, noise and vibration caused by the equipment, semi-product's, additives' and finished product's dusts, fluorine- and phosphorus-containing substances' affects and poor illumination. The proposed data were used for health-related improvements in the occupational conditions.