This study was conducted to evaluate the degree of mobility and fractionation of cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) after the addition of municipal solid sewage sludge (MSS) in a sandy calcareous soil.

Purpose Sorption, desorption, and leaching of metals in the sediments of the aquatic environment are paramount important in their bioavailability. Also, behavior of these metals in such sediments as the riverbed sediments is affected by the characteristics of the sediments such as grain size, pore size distribution, and pH of the medium. Four riverbed sediments with varying properties were artificially contaminated with cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). Then, using leaching columns, they all were subjected to drying and wetting phases to study the competitive binding and release of metals. Materials and methods Sediment samples were collected from 0 to 10 cm depth of Abshineh and Ghareh Chai River during the dry season. Samples were spiked with 400 mg Zn kg −1 , 200 mg Cu kg −1 , 200 mg Ni kg −1 , and 50 mg Cd kg −1 (dry weight equivalent) in plastic container and then after drying seated at a height of 10 cm in leaching column. Sediment columns were incubated at room temperature (22-24°C) and leached with 10-20 pore volumes (PVs) with distilled water. The distribution of metals over different extractable fractions was evaluated before leaching. Results and discussion The four metals were separated into two classes according to their leachability. In the sediment columns that contained more clay, commonly mobile metals like Zn, Ni, and Cd that appeared to be rather immobile and commonly immobile metals like Cu were unexpectedly quite mobile. The observation that copper leachability was higher for the sediments with finer grain size and higher organic matter content indicates that pore size distribution, the presence of organically complexes, and colloidal particles, may have had major role in this mobility behavior of copper. The mobility of Zn and Cd are strongly governed by pH, where the mobility of Cd is typically much greater than Zn under acidic conditions. The metal addition caused the displacement of Ca, Mg, K, and Na their subsequent leachate from the spiked sediment columns. Conclusions Despite the spiking of inorganic metals into the sediments and drying before leaching, the mobilization of metals with distilled water (to mimic rainwater) was small in the different sediments relative to the total amounts of each metal added. This would indicate that the major part of the added metals were likely to be bound in forms that exhibit a low potential for release to the environment and low bioavailability to organisms.

Leaching column experiments were conducted to determine the degree of mobility of heavy metals (HMs) and nutrients after the addition of municipal solid sewage sludge (MSS) in a sandy-loam soil. Treatments were (1) soil application of low metal content MSS, (2) soil application of metal-enriched municipal solid sewage sludge (EMSS), and (3) control. The MSS application represented a dose of 200 Mg dry weight (dw) ha -1 . Soil columns were incubated at room temperature for 15 d and were irrigated daily with distilled water to make a total of 557 mm. Leachates were collected and analyzed for HMs and nutrients. The Ni and Pb added to soil via MSS and EMSS were found to be leached through the 20 cm columns of calcareous sandy soil although Ni and Pb concentrations in the percolate were small relative to the total amounts of metals applied. Losses of K + from the EMSS, MSS, and control were 92.5, 82.0, and 52.5 kg ha -1 , respectively. Losses of Mg 2+ were in the range from 104.4 (control treatment) to 295.2 kg ha -1 (EMSS), while the loss of Ca 2+ was in the range from 265.0 (control treatment) to 568.2 kg ha -1 (EMSS). The results showed that the amounts of P leached from EMSS (3.02 kg ha -1 ) and MSS (2.97 kg -1 ha -1 ) were significantly larger than those from the control treatment (1.54 kg ha -1 ). The geochemical code Visual MINTEQ was used to calculate saturation indices. Leaching of P in different treatments was controlled by rate-limited dissolution of hydroxyapatite, b-tri-Ca phosphate, and octa-Ca phosphate. The results indicate that application of MSS to a sandy soil, at the loading rate used in this study, may pose a risk in terms of groundwater contamination with Ni, Pb, and the studied nutrients.

Impact of anthropogenic loading of phosphorous (P) to an aquatic ecosystem can be qualitatively assessed by measuring the buildup and distribution of P in sediments and by differentiating bioavailable and recalcitrant P pools. Distribution of P pools in sediments is affected by the physico-chemical properties including specific elements, particle size distribution, pH, electrical conductivity (EC), and carbonate content. We applied X-ray fluorescence and scanning electron microscopy (SEM) methods to characterize sediments from western rivers in the Urmia Lake basin in Iran with a particular focus on properties that are relevant to P speciation. Phosphorous pools were sequentially extracted into operationally defined exchangeable (EXCH-P), iron and aluminum oxide-bound (Fe/Al-P), calcium-bound (Ca-P), and residual (RES-P) P pools. In river sediments, the size of P pool was found to be in the order of Ca-P > RES-P > Fe/Al-P > EXCH-P indicating small fraction of bioavailable P pool and Ca-P minerals being the most dominant P sink. Carbonate-related properties had an inverse relationship with bioavailable P pools in the river sediments studied. The principal component analysis (PCA) of the sequential extraction data with sediment properties revealed that four principal components described 82.7% of total variation. Similarly, particle size-related properties were found to have the highest eigenvalues in the first PC. Electron diffraction spectra (EDS) and X-ray fluorescence (XRF) analyses showed a largely uniform distribution of P in the upstream sediment. However, limited evidence of local enrichment of P with Fe, Al, and Ca contents was observed in the downstream river sediments. Correlation of Fe/Al-P pool size with AlO and SiO contents indicated that P was associated with Al oxide and clay minerals in the sediment matrix. Overall, the results from this study provide insights into the variability of upstream and downstream river processes and their relationship with P pools with regard to their bioavailability. These results are expected to be useful in assessing the potential impact of P loading on the aquatic ecosystem in the Urmia Lake basin.