Evaluating solubility, aggregation and sorption of nanosilver particles and silver ions in soils

Engineered nanoparticles (ENPs) are used in so many different products. ENPs are released into different environmental compartments. Silver nanoparticle (AgNP) is one of the most used ENPs. AgNPs may cause damage to the environment due to their toxicity and wide exposure. In this thesis possible exposure ways of AgNPs to the environment was reported. Also sorption-solubility and aggregation of AgNPs and AgNO3 based on the different concentration of Ag and pH function in clayey and sandy soil was investigated. Results showed that sorption of both silver nanoparticles and silver ions by the soils were increased with increasing pH. Silver (nano/ion) sorption ratio in clayey treatment was slightly higher than sandy one. It can be due to having higher CEC value and finer texture in clay in comparison with sand. Partitioning between nanosilver and free silver ions was investigated by help of ultrafiltration. It can be concluded that a significant fraction of the silver nanoparticles were oxidized and transformed to free Ag+ during the oxic experimental conditions. The aggregation of AgNPs and silver ions was investigated based on the different concentration of silver in a constant pH. Aggregation of silver nanoparticulate by help of SEM and XRD were identified in 2.5 ppm concentration of AgNPs in sandy soil. No aggregation was found at low concentration of silver nanoparticles. No silver aggregated spot could be recognized at 6.7, 0.65 and 0.05 ppm concentration of silver in silver nitrate polluted soil samples

Chromium(III) Complexation to Natural Organic Matter: Mechanisms and Modeling

Chromium is a common soil contaminant, and it often exists as chromium­(III). However, limited information exists on the coordination chemistry and stability of chromium­(III) complexes with natural organic matter (NOM). Here, the complexation of chromium­(III) to mor layer material and to Suwannee River Fulvic Acid (SRFA) was investigated using EXAFS spectroscopy and batch experiments. The EXAFS results showed a predominance of monomeric chromium­(III)-NOM complexes at low pH (<5), in which only Cr···C and Cr–O–C interactions were observed in the second coordination shell. At pH > 5 there were polynuclear chromium­(III)-NOM complexes with Cr···Cr interactions at 2.98 Å and for SRFA also at 3.57 Å, indicating the presence of dimers (soil) and tetramers (SRFA). The complexation of chromium­(III) to NOM was intermediate between that of iron­(III) and aluminum­(III). Chromium­(III) complexation was slow at pH < 4: three months or longer were required to reach equilibrium. The results were used to constrain chromium-NOM complexation in the Stockholm Humic Model (SHM): a monomeric complex dominated at pH < 5, whereas a dimeric complex dominated at higher pH. The optimized constant for the monomeric chromium­(III) complex was in between those of the iron­(III) and aluminum­(III) NOM complexes. Our study suggests that chromium­(III)-NOM complexes are important for chromium speciation in many environments