Carboxyl latex particles of two different sizes were used to study the early stages aggregation in dilute colloidal suspensions. The charging behavior as a function solution pH was characterized acid−base titration and electrophoresis experiments at fixed ionic strength; absolute rate constants measured by combined static dynamic light scattering strength. Up an strength 10 mM KCl solution, classical DLVO theory stability is seen work quantitatively. At higher strength, however, well-known...

Proton binding by a soil fulvic acid, humic and set of size fractions the acid was studied as function pH ionic strength potentiometric titrations. The negative charge substances resulting from deprotonation acidic functional groups generally increased with increasing strength. At any given strength, fraction exhibited much higher than fraction. For size-fractionated acids, decreased steadily apparent molecular weight, determined exclusion chromatography. Observed differences in proton...

Water management in paddy soils can effectively reduce the soil-to-rice grain transfer of either As or Cd, but not both elements simultaneously due to higher mobility under reducing and Cd oxidizing soil conditions. Limestone amendment, common form liming, is well known for decreasing accumulation rice grown on acidic soils. Sulfate amendment was suggested decrease rice, especially intermittent flooding. To study unknown effects combined sulfate limestone flooding we performed a pot...

Binding of Cu(II) and Pb(II) to a soil fulvic acid, humic two different size fractions the acid was investigated with metal titration experiments at pH 4, 6, 8. Proton free ion activities in solution were monitored after each step using selective electrodes (ISE), respectively. The amounts base required maintain constant conditions recorded used calculate stoichiometric proton-to-metal exchange ratios. Despite clear differences chemical composition protonation behavior, all exhibited very...

Summary To investigate the chemical heterogeneity of humic substances in relation to molecular size, fulvic and acids were extracted purified from surface horizon a Humic Gleysol northern Switzerland. A fractionation scheme using hollow‐fibre ultrafiltration cartridges was developed used obtain four size fractions acid with nominal weight ranges > 300 kDa, 100–300 30–100 10–30 kDa. The all characterized by exclusion chromatography, elemental analysis (C, H, N, S), as well spectroscopic...

Colloid release and deposition in soils sorption of inorganic organic pollutants to soil colloids are strongly influenced by the composition chemical heterogeneity colloidal particles. To investigate at particle scale, we used synchrotron scanning transmission X-ray microscopy (STXM) C-1s near-edge absorption fine structure (NEXAFS) spectroscopy on 49 individual particles isolated from surface horizons three forest soils. Stacks 130 images each were collected different energies between 280...

The influence of cation-induced coagulation on the chemical composition dissolved and coagulated fractions humic acid was investigated in batch experiments for additions aluminum at pH 4 5, iron 4, calcium lead 6. partitioning organic carbon metals determined by analyzing total metal contents phase. Both were characterized using synchrotron scanning transmission X-ray microscopy (STXM) C-1s near-edge absorption fine structure (NEXAFS) spectroscopy. Intensities π* transitions carboxyl σ*...

Previous studies on proton and metal binding to humic substances have not considered a potential influence of reduction oxidation functional groups. Therefore, we investigated how purified soil acid was affected by reduction. Reduction the carried out using an electrochemical cell that allowed us measure amounts electrons protons involved in reactions. We further applied spectroscopic methods (UV−vis, fluorescence, FT-IR, C-1s NEXAFS) detect possible chemical changes induced reoxidation. The...

Iron oxides and oxyhydroxides are important sorbents for arsenic in soils, sediments, water treatment systems, but their long-term potential retention may be diminished by the formation of polymeric silicate on surfaces. To study these interactions, we first investigated sorption to colloidal hematite (α-Fe(2)O(3)) short-term (48 h) (210 days) batch experiments. The polymerization surface was monitored attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. pH...

Natural organic matter (NOM) exerts strong influence on copper speciation and bioavailability in soils aquatic systems. In redox-dynamic environments, electron transfer reactions between redox-active moieties of NOM may trigger Cu(I) Cu(0) formation. To date, little is known about Cu-NOM redox interactions binding to NOM. Here, we present X-ray absorption spectroscopy results transformations upon addition Cu(II) or untreated electrochemically reduced soil humic acid (HA) under oxic anoxic...

We investigated the influence of humic and fulvic acid concentration (in range 1-1000 mg/L) on binding two trace metals Cu(II) Pb(II). The ability non-ideal competitive adsorption (NICA)-Donnan model to correctly predict Cu Pb at low or lower ionic strength (0.01 M NaNO3), based parameters obtained from experiments conducted high concentrations (approximately 1000 higher (0.1 was tested. in 0.01 NaNO3 determined over wide ranges proton metal ion activities using three different methods:...

Sorption of sulfathiazole (STA) and three structural analogs to Leonardite humic acid (LHA) was investigated in single- binary-solute systems elucidate the sorption mechanism sulfonamides soil organic matter (SOM). Cation binding STA+ anionic sites A− LHA governed up circumneutral pH, based on following findings: (i) From pH 7.7 3.3, increase extent nonlinearity (i.e., concentration dependence) STA paralleled STA+. (ii) 3.3 1.7, decreased increased, consistent with strong competition H+ for...

Naturally occurring variations of redox conditions are considered to affect the interactions between trace metals and humic substances in a 2-fold manner. First, additional proton binding sites formed under reducing may also act as for metals. Second, reduced transfer electrons redox-active In this study, we investigated influence electrochemical reduction purified soil acid on two chalcophile metal cations environmental concern, Cd2+ Ag+, with titrations conducted monitored conditions. The...

Numerous ionizable organic micropollutants contain positively charged moieties at pH values typical of environmental systems. Describing cation and zwitterion interaction with dissolved natural matter requires explicit consideration the pH-dependent speciation both sorbate sorbent. We studied pH-, ionic strength-, concentration-dependent binding relatively large, cations zwitterions (viz., antibiotics clarithromycin tetracycline) to humic acid in absence presence Ca2+ evaluated ability...

In submerged soils and sediments, clay minerals are often exposed to anoxic waters containing ferrous iron (Fe2+). Here, we investigated the sorption of Fe2+ onto a synthetic montmorillonite (Syn-1) low in structural Fe (<0.05 mmol per kg) under conditions effects subsequent oxidation. Samples were prepared at two Fe-loadings (0.05 0.5 mol added kg clay) equilibrated for 1 30 days (O2 < 0.1 ppm), followed by exposure ambient air. Iron solid-phase speciation mineral identity was analysed 57Fe...

Accumulation of inorganic arsenic (iAs) and dimethylarsenate (DMA) in rice threatens human health yield, respectively. We studied the yet unclear interactions soil sulfate amendment water management for decreasing As accumulation grain a pot experiment. show that (+200 mg S/kg soil) decreased iAs by 44% without clearly increasing DMA under intermittent flooding from booting stage to maturation. Under continuous during this period, only 25% but increased 68%. The mechanisms effects on were...

Abstract We performed a detailed study on the carbon build‐up over 140‐year‐long chronosequence of D amma glacier forefield, S witzerland, to gain insights into organic dynamics during initial stage soil formation and ecosystem development. determined nitrogen contents their stable isotopic compositions, as well molecular‐level composition bulk soils, recalcitrance parameters in different fractions. The was divided three age groups, separated by small end moraines that resulted from two...

Representing the staple crop for half of world population, rice can accumulate high levels cadmium (Cd) in its grain, posing concerns on food safety. Different soil amendments have been proposed to decrease Cd accumulation grain by either decreasing availability, introducing competitive ions uptake, or down-regulating expression transporters uptake. However, effectiveness applied alone combinations needs be tested under field conditions. Here, we present results trials with two cultivars...