Browsing by Subject "Cadmium"

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Heavy metals from phosphate fertilizers in maize-based food-feed energy systems
(2023) Niño Savala, Andrea Giovanna; Fangmeier, Andreas
The problem of polluted agricultural lands with heavy metals due to anthropogenic activities, including applying phosphorous (P) fertilizers polluted with cadmium (Cd) and other metal such as uranium, has been extensively studied. Several reviews, including the one in the present dissertation, have elaborated this issue with often the same results: the application of P fertilizers with high Cd levels is strongly correlated to Cd accumulation in arable soil, which could imply environmental risks as well as health risks for humans and animals through the food chain. Therefore, these reviews have often the same conclusion: the application of low Cd-P fertilizers, either mineral, organic or recycled, is diminishing the risks of Cd pollution at the soil, crop and consumption level. However, globalization, trade politics, economy, dependency on Morocco mineral P fertilizers, and the finite stock in the raw material have challenged this possibility, especially in the European Union. Meanwhile, in China, polluted arable soils are related to other anthropogenic activities and type of fertilizers rather than Cd-polluted phosphate rock and mineral P fertilizers. At the farm level, other options to diminish Cd pollution in soil and crops, besides low Cd-P fertilizers, could consist of different fertilizer and crop management. These options were studied in this dissertation. A different P management, including different rate applications and placements, did not influence the total Cd concentration in silage maize grown in Germany, regardless of the developmental stage of the crop and the Cd levels in P fertilizer. Silage maize might take up Cd derived from P fertilizers under unpolluted soils, without high risks due to its high biomass production. However, significant changes in the labile Cd fraction were already visible after applying Cd-polluted P fertilizers at 150% of the required amount to the soil after only two growing seasons. Further research should be done to understand the correlations between the bioavailable metal fraction and the actual Cd uptake by silage maize, especially in unpolluted soils. This recommendation also follows the meta- analysis results presented in the second publication, which indicated a possible bias as most of the studies are performed under polluted conditions. Considering the results of the third and fourth publication, the Cd uptake by silage maize was strongly correlated to labile Zn in the soil and the Zn uptake at the early development stage after two field seasons. Placed P fertilizer had a significant and negative effect on the Zn uptake by young silage maize. Further research is needed to understand the behavior of Cd and Zn in the uptake process by maize under P fertilization in unpolluted soils. According to three of the four publications presented in this dissertation, the soil pH was the main soil characteristic influencing the bioavailability and the plant uptake of Cd under unpolluted conditions, regardless of the P treatment, the development stage, and the maizes intended use. However, the total Cd concentration in the soil was the dominant variable for the Cd concentration in maize grain when the soil was polluted with high Cd levels, which was the case in several experiments analyzed in the second publication. P fertilizers with average Cd contamination might enhance labile Cd accumulation in arable land and crops when applied to low biomass crops, such as wheat and legume crops. In this regard, crop management such as crop rotation in the central field experiment indicated that the wheat rotation induced a lower Cd accumulation in maize-soil systems, owing to wheat likely accumulating Cd at higher levels than other crops. The results presented in the second publication also indicated high Cd accumulation by the wheat crop: the wheat grain accumulated more Cd than the maize grain. Thus, potential hazards related to Cd accumulation in wheat grain should also be considered in wheat-maize systems. In conclusion, suitable crop rotations considering the crop-specific potential of Cd accumulation, efficient P management including soil P levels and nutrient use efficiency, and low Cd-P fertilizers remain the most viable options and the main challenge to avoid Cd accumulation in arable soils.
Removal of organic and inorganic pollutants from aqueous solutions by organically modified clayey sediments
(2012) Mubarak, Dalia Mohamed Fahmy; Müller, Torsten
Re-use of agricultural drainage water and industrial wastewater is one of the adopted strategies in different countries to close the gap between water resources and water demands. Drainage and industrial wastewater contain varieties of toxic pollutants that can potentially cause hazard on humans and environment. Although adsorption techniques are considered one of the proper methods for the wastewater treatments, economic aspect is a crucial factor for the broad application of such technique. Addressing this, the thesis concerns on proposing sorbents having the potential to remove heterogeneous pollutants simultaneously, particularly taken in consideration the limited resources in developing and emerging countries, in this study exemplified for Egypt. For this purpose, natural clayey sediments as cheap and environmentally friendly materials were used in combination with various organic modifiers to produce of organically modified clayey sediments (OMCs). In contrast to the natural clayey sediments, OMCs are expected to have the ability to remove heterogeneous pollutants including anionic and cationic as well as organic and inorganic pollutants. The sorbability and desorbability characteristics of OMCs were investigated for Cd2+ and Pb2+ (cationic ), Cr2O72- (anionic-) and metalaxyl m (MM; organic-pollutants). The basic clay materials in OMCs were naturally occurring kaolinitic (kao sediment) and bentonitic (bent sediment) clayey sediments distributed widely in Egypt. Different concentrations of the organic modifiers L-Carnitine (Carnitin), L Cystine dimethyl ester (Cys_ester), Methyltriphenyl-phosphonium (MTP) or Hexadecyltrimethyl-ammonium (HDTM) were employed. The modification of natural clayey sediments with organic modifiers increased the organic carbon contents of OMCs following the order Carnitin < Cys_ester < MTP < HDTM. OMCs based on bent sediments had a higher loading of the organic modifiers than those based on kao sediments and the loading increased with increasing the used concentrations of the organic modifiers. To characterize and confirm the modification of OMCs, the prepared materials were analyzed by mid infrared spectroscopy (MIRS). The obtained spectra showed shifting of the vibration bands of the natural clayey sediments, and depicted the characteristic vibrations bands of the organic modifiers, indicating the interaction between the natural clayey sediments with the organic modifiers and the successful loading. Further analysis by X ray diffraction showed that the modification of OMCs based bent sediments with MTP or HDTM caused an expansion of the interlayer spacing of the clay from 14.5 Å to 17.1 or 19.7 Å, respectively; reflecting a bilayer or pseudo-trimolecular arrangements of MTP or HDTM, respectively, in the clays interlayer. The loading ratios of the organic modifiers on OMCs as a percentage of the CEC of the natural clayey sediments were also calculated. Following the characterization of OMCs, screening experiments were conducted to select the suitable concentration of each organic modifier to be loaded in order to achieve the highest removal of heavy metals. The results showed that loading of OMCs based on kao sediments by HDTM and Carnitin at concentrations equal to or higher than 71and 8 % of the CEC of the natural kao sediment, respectively, caused no relevant differences in the sorption of Cd2+ and Pb2+ compared to natural kao sediment. However, the loading of Cys_ester and MTP at concentrations equal to 38 and 21 % of the CEC or higher increased the sorption of those metal ions. Remarkable enhancements in the sorption of Cr2O72- were obtained by the modification of OMCs based kao sediments with HDTM and Cys_ester. The outcome from these screening experiments with OMCs based bent sediments can be concluded as follow: HDTM and MTP at loading concentrations > 50 % of the CEC of the natural bent sediments were able to remove all Cd2+ and Pb2+ from the solutions. However, increasing the loading concentration of Cys_ester decreased the sorption of those metal ions as compared to natural bent sediment. OMC modified with Carnitin at loading concentration up to 21 % of the CEC was able to remove 84 % of Cd2+ and 100 % of Pb2+ from the solutions but a further increase of Carnitin loading decreased the sorption of the metal ions. The OMCs modified with HDTM and Cys_ester were very efficient in removing Cr2O72- from the solutions and the removal increased with increasing loading concentrations of the organic modifiers. The OMCs based on bent sediments loaded with HDTM, MTP, Carnitin and Cys_ester at loading concentrations equal to 102, 79, 18 and 66 % of CEC of the natural bent sediments, respectively, and in addition OMC loaded with Humic acid (HA), were selected as promising sorbents to test the sorbability and desorbability of OMCs with respect to the pollutants. The sorption processes were investigated as function of the metal concentration, sorption time, the initial solution pH and the electrolyte concentration. OMCs modified with HDTM, MTP, HA and Carnitin showed high sorbability for Cd2+ and Pb2+. However, OMCs modified with Cys_ester displayed the best sorbent for Cr2O72-. OMCs were successful to remove almost all Cd2+, Pb2+ from the solutions at wide ranges of pH; 4-8 and 4-6, respectively, while the optimum for the sorption of Cr2O72- was pH 4. The Langmuir model described adequately the observed sorption data of Cd2+ and Pb2+ on all sorbents and Cr2O72- on OMC modified with Cys_ester better than the Freundlich model. The sorption followed the pseudo second order kinetics with the rate constants demonstrating faster sorption on OMCs with Carnitin and HA for Cd2+ and Pb2+ and faster sorption on OMCs with MTP and Cys_ester for Cr2O72-. Sorption of Cd2+ and Pb2+, particularly on OMCs with Carnitin and HA, were decreased with increasing electrolyte concentrations. Whereas, increasing the electrolyte concentrations enhanced the sorption of Cr2O72- to OMC with Cys_ester. OMCs showed ability to release the sorbed heavy metals, which shows the potential for re-using. The presence of other solutes in the binary and ternary component systems strengthened the sorption of Cr2O72- on OMCs based bent sediments with HDTM and MTP and enhanced the sorption of MM on OMCs with Cys_ester and MTP. Competition phenomena were recorded for the sorption of Cd2+ and MM on OMC with HDTM. No competition behaviours were observed in the sorption of the tested pollutants on OMC with Cys_ester. OMCs with HDTM, MTP and Cys_ester were able to remove Cd2+, Cr2O72- and MM simultaneously from the binary and ternary component systems. The results indicate the prospective application of the OMCs in the treatments of natural agricultural drainage water and industrial wastewater.
Zum Einfluß von mikrobieller Phytase und Calcium auf die Blei-, Cadmium und Zinkretention beim wachsenden Schwein
(1997) Zacharias, Bernhard; Drochner, Winfried
In the present study the influence of microbial phytase and/or calcium supplementation in rations of growing pigs (15 to 30 kg resp. 50 kg) on the retention of lead, cadmium and zinc in kidneys, liver, muscles and bones was investigated. The rations consisted of a barley-soy mixture supplemented with lead, cadmium and zinc either in the form of Pb-, Cd- and Zn-polluted barley or of CdCl2, Pb(CH3COO)2, and ZnSO4. The rations contained an average of 1,45 mg Pb, 0,78 mg Cd, and 55,7 mg Zn per kg dry matter and were given either with or without an addition of 800 U microbial phytase per kg. Compared to the reference group the addition of microbial phytase resulted in diets with a nomal calcium supply (6 g/kg) to a significant increase in the concentration of lead in the phalanx 1 and cadmium in kidneys and liver. The zinc concentration, however, only was increased in tendency in bones and liver. By augmenting the calcium concentration to 12 g/kg it was possible to avoid phytase-induced increase in the retention of lead in phalanx 1 and in the deposition of cadmium in kidneys and liver. For zinc, however, this effect of calcium could not be detected. The higher lead concentration in liver, kidneys and bones after addition of Pb(CH3COO)2 may be due to the 51 higher dietary Pb level as compared to the normally polluted barley rations. The reduced Cd-accumulation in livers and kidneys after feeding CdCl2 supplemented diets with a high calcium level may be explained by an increased formation of insoluble cadmium-calcium-phytate that cannot be hydrolysed by phytase. For the heavy metals lead, cadmium, and zinc the addition of phytase might probably result in an increased metal availability due to phytase-induced hydrolysis of the phytate complex. The effect of a calcium supply exceeding the recommended level may be explained by a reduction in the solubility of phytate which results in a decreased ability of phytate to be splitted by phytase and therefore leads to a reduced