Adsorption des métaux lourds (Cu, Zn, Cd et Pb) par les sédiments superficiels d'un cours d'eau: rôle du pH, de la température et de la composition du sédiment

Une étude expérimentale concernant l'adsorption des métaux lourds Cu, Cd, Zn et Pb par des sédiments d'un cours d'eau pollué par des rejets industriels a été entreprise pour mettre en évidence l'importance de certains paramètres expérimentaux, notamment le pH, la masse de sédiments et la température. Elle a permis également d'analyser la nature des liens qui participent à la fixation des cations métalliques sur les différentes fractions sédimentaires déterminées selon la méthode de TESSIER et al. (1979) et d'interpréter les capacités d'adsorption relativement variables suivant la nature du métal. Les résultats confirment le rôle particulier des fractions réductible (oxydes de fer et de manganèse) et organique (substances humiques en particulier), dont les propriétés respectives d'échange d'ions et de complexation ont été souvent vérifiées. La capacité d'adsorption de ce sédiment a notamment pu être interprétée en termes d'isothermes d'adsorption en exploitant les modèles de Langmuir et de Freundlich et leurs équations linéarisées.In an experimental study of the adsorption of Cu, Cd, Zn and Pb by surface sediment in a small stream polluted by the industrial drain of electro-refinery, we have demonstrated the irnportance of some such experimental parameters as pH, sediment concentration and temperature. These experiments were conducted in batch systems at constant temperature with continuous agitation, using a mixture of sediment and metals at an adjusted pH; the quantity of metals remaining in solution was determined by a polarographic method. Adsorption percentages for the concentratons of sediment (200 and 1000 mg/L) and metals (1 mg/L) reached the following maximum values: Pb (99-l00%o), Zn (80-90 %), Cd (75-85 %) and Cu (70-80%). These variations in metal soprtion are attributed to differences in binding energy between the metallic cation and the sediment sites, when all other parameters are fixed. Based on metal partitioning among the different sedimentary fractions, as determined according to the sequential extraction method of TESSIER et al. (1979), it was possible to attribute metal adsorption to complexation, coprecipitation and complexation reactions respectively with organic matter, carbonates and Fe-Mn oxides or alumino-silicates. Our results highlight the specific roles played by the reducible Fe-Mn oxides and by humic substances. Fulvic and humic acids, which are considered as the stable fraction of sedimentary organic matter, can form complexes and participate in the fixation of metals on the sediments (GODFRIN and BLADEL, 1990; WILLIAM and HANSON, 1979; FITCH et al., 1968; BIZRI et al., 1985). The stability of these complexes depends on the variety of reaction sites in these macromolecules, which in turn determines the degree of fixation of the cations (specific adsorption). Concerning the iron-manganese oxides and the alumino-silicate compounds, their surface sites are engaged insurface complex formation by a mechanism of proton exchange in which humic substances can be also involved (BELZILE et al., l989a; BELZILE and TESSIER, 1900; BELZILE et al., 1989b).Adsorption kinetics for Cu, Zn and Cd were relatively fast with more than 50 % of the metal adsorbed in a few hours, followed by a partially reversible stage over the next few days leading to an equilibrium state. Reversibilty of Pb binding was not signifrcant (attributed to the chemical precipitation of Pb3(PO4)2). An enhancement of adsorption with increasing pH between 5 and 8 was noted for Cu, Zn and Cd. Several factors may contribute to this increase in the quantity of absorbed metals:-the M+ and MOH+ species berome more competitivethan H+ fortte adsorption sites on the sediment;- the number of adsorption sites increases;- the change in conformation of the humic substances, from aggregated to stretched forms, may render the metal complexing sites more accessible;- the rate of Fe(III) and Mn(IV) formation is more significant at higher pH values;- at higher pH, the precipitation of oxides, hydroxides and hydroxycarbonates becomes important as well as the adsorption on the suspended phases;- the degree of oxide crystallization is influenced by the pH value and hence the adsorption capacity of reducible phases is also affected.A decrease in metal adsorption was also observed as the temperature increased between 10°C and 40°C. The adsorption of metals was described using FREUNDLICH and LANGMUIR equations in their linear form

Growth performance, blood lipids, and fat digestibility of broilers fed diets supplemented with bile acid and xylanase

This study aimed to show the effect of bile acid (BA) and xylanase (Xyl) supplementation on the growth, fat digestibility, serum lipid metabolites, and ileal digesta viscosity of broilers. A total of 720 1 d old male broilers were allocated to one of nine treatments with four replicates in each under a factorial design arrangement of three levels of BA (0 %, 0.25 %, and 0.50 %) and three levels of Xyl (0 %, 0.05 %, and 0.10 %) supplementation. The duration of the experiment was 35 d (7–42 d). Growth performance, blood lipids, fat digestibility, and ileal digesta viscosity were determined. The experimental treatments did not affect feed intake (FI) and weight gain (WG). Supplementation of BA or Xyl did not significantly ameliorate the feed conversion rate (FCR) (p&lt;0.05). The addition of BA linearly increased fat digestibility. At 7–21 d of age, the addition of BA or Xyl had a significant (p&lt;0.05) increase in serum cholesterol (Chol) but no significant difference for other serum lipid parameters in broiler chickens fed with Xyl in the starter and grower periods. However, the supplementation of 0.5 % BA at 7–21 d of age significantly increased the Chol and low-density-lipoprotein (LDL) levels. The results of this trial revealed that the supplementation of xylanases had a great effect on the degradation of arabinoxylan from wheat, which led to a relatively greater reduction in ileal digesta viscosity; it was also found that supplementation of BA significantly increased the concentration of serum lipid metabolites, whereas BA and Xyl supplementation linearly increased the fat digestibility of the birds fed wheat and tallow diets.</p

Développement d'une méthode simple en vue de la détermination directe de la concentration en As(III) et en arsenic inorganique total, dans les eaux de boissons

L'abaissement de la teneur maximale admissible d'arsenic à 10 µg.L-1 dans les eaux destinées à la consommation humaine en France, conduit à la recherche de méthodes de dosage de l'arsenic à la fois simples et peu coûteuses, étant donné le suivi analytique à mettre en oeuvre, en particulier sur les ressources de faibles débits. L'arsenic se trouve principalement dans les eaux naturelles sous forme inorganique As(V) et As(III) ; cette dernière forme étant plus toxique et moins bien éliminée dans les filières de potabilisation que As(V). Par conséquent, outre ta teneur totale en arsenic inorganique, il est important connaître le degré d'oxydation de l'arsenic. De plus, les espèces sont susceptibles d'évoluer dans le temps : As(III) pouvant être oxydé en As(V) par simple contact avec l'air. A partir de la méthode de dosage de l'arsenic total par Spectrométrie d'Absorption Atomique Flamme, couplée à la Génération d'Hydrure, une méthode de détermination des formes inorganiques de l'arsenic a été mise au point et optimisée. Le développement de cette méthode est basée sur le fait que, lors de l'analyse, l'arsenic (V) est réduit ou non en arsenic (III) selon le pH. Ainsi, le dosage de l'As(III) seul est obtenu en remplaçant HCl, utilisé pour le dosage de l'arsenic total, par un acide faible : l'acide citrique. Cette méthode a été validée et testée sur une eau synthétique, spécifique d'une région, ainsi que sur des échantillons d'eaux réels et une solution de matériau certifié

Effect of petroleum crude oil on mineral nutrient elements and soil properties of jojoba plant (Simmondsia chinensis)

This study evaluated the effect of petroleum crude oil contaminated soil on the mineral nutrient elements, soil properties and bacterial biomass of the rhizosphere of jojoba plant (Simmondsia chinensis). Malondialdehyde (MDA) concentration increased in jojoba leaves when grown in petroleum oil polluted soil especially at 2% and 3% crude oil. It was noted that Na, Mg and Ca decreased, while K increased in shoots of jojoba. In roots Na and Ca increased, however K and Mg decreased with increasing crude oil concentration in the soil. Heavy metals, Cu, Mn, Cd and Pb increased in both shoot and root with increasing crude oil concentration, while Zn decreased comparing with the control. In soil, N and K decreased, meanwhile Cu, Fe, Mn and Zn as well as organic matter increased with increasing crude oil concentration. Soil was free from P, while the addition of inorganic fertilisers improved P content. Bacterial account was significantly increased at the end of the experiment at 1% and 2% crude oil, especially after addition of inorganic fertilisers. The electrical conductivity and MDA of the leaves increased with increasing crude oil concentration in the soil. The addition of inorganic fertilisers to crude oil contaminated soil decreased the electrical conductivity and MDA comparing with crude oil only

Effect of Petroleum Crude Oil on Mineral Nutrient Elements, Soil Properties and Bacterial Biomass of the Rhizosphere of Jojoba

Aims: This study is to evaluate the effect of petroleum crude oil contaminated soil on the mineral nutrient elements, soil properties and bacterial biomass of the rhizosphere of jojoba plants (Simmodsia chinensis). Methodology: A pot experiment was carried out. The soil was treated with different levels of crude oil: 1, 2 and 3% v/w either alone or in combination with inorganic fertilizers. Results: Malondialdehyde (MDA) concentration increased in jojoba leaves when grown in petroleum oil polluted soil especially at 2% and 3% crude oil. It was noted that, Na, Mg and Ca decreased while K increased in shoots of jojoba. In roots Na and Ca increased however K and Mg decreased with increasing crude oil concentration in the soil. Heavy metals, Cu, Mn, Cd and Pb increased in both shoot and root with increasing crude oil concentration while, Zn decreased comparing with the control. In soil, N and K decreased meanwhile Cu, Fe, Mn and Zn as well as organic matter increased with increasing crude oil concentration. Soil was free from P while, the addition of inorganic fertilizers improved P content. Bacterial account was significantly increased at the end of the experiment at 1% and 2% crude oil especially after addition of inorganic fertilizers. The electric conductivity and MDA of the leaves increased with increasing crude oil concentration. The addition of inorganic fertilizers to crude oil contaminated soil decreased the electric conductivity and MDA comparing with crude oil only. Conclusion: The observed changes in composition of mineral elements in jojoba plants in the present study could be attributed to the cell injury and disruption in the cell membrane, heavy metal accumulation and toxic nature of the petroleum oil. Also this study has demonstrated that soil contamination with crude oil has a highly significant effect of reducing some mineral element composition of Jojoba plants

Development of a clinical risk score to predict death in patients with COVID-19

Objective: To build a clinical risk score to aid risk stratification among hospitalised COVID-19 patients. Methods: The score was built using data of 417 consecutive COVID-19 in patients from Kuwait. Risk factors for COVID-19 mortality were identified by multivariate logistic regressions and assigned weighted points proportional to their beta coefficient values. A final score was obtained for each patient and tested against death to calculate an Receiver-operating characteristic curve. Youden's index was used to determine the cut-off value for death prediction risk. The score was internally validated using another COVID-19 Kuwaiti-patient cohort of 923 patients. External validation was carried out using 178 patients from the Italian CoViDiab cohort. Results: Deceased COVID-19 patients more likely showed glucose levels of 7.0–11.1&nbsp;mmol/L (34.4%, p&nbsp;&lt;&nbsp;0.0001) or &gt;11.1&nbsp;mmol/L (44.3%, p&nbsp;&lt;&nbsp;0.0001), and comorbidities such as diabetes and hypertension compared to those who survived (39.3% vs. 20.4% [p&nbsp;=&nbsp;0.0027] and 45.9% vs. 26.6% [p&nbsp;=&nbsp;0.0036], respectively). The risk factors for in-hospital mortality in the final model were gender, nationality, asthma, and glucose categories (&lt;5.0, 5.5–6.9, 7.0–11.1, or 11.1&nbsp;&gt;&nbsp;mmol/L). A score of ≥5.5 points predicted death with 75% sensitivity and 86.3% specificity (area under the curve (AUC) 0.901). Internal validation resulted in an AUC of 0.826, and external validation showed an AUC of 0.687. Conclusion: This clinical risk score was built with easy-to-collect data and had good probability of predicting in-hospital death among COVID-19 patients