Copper--alumina--organic matter mixed systems: alumina transformation and copper speciation as revealed by EPR spectroscopy

Environmentally persistent free radical generation on contaminated soil and their potential biotoxicity to luminous bacteria

Environmentally persistent free radicals (EPFRs) are detected in the clay, mineral or humic part of the soil, especially in soil contaminated with phenolic compounds. To clarify the detailed information on the formation of EPFRs, we used the contaminated soil with catechol to mimic their formation process in laboratory scale and tested their biotoxicity with luminescent bacteria (Photobacterium phosphoreum, P. phosphoreum). Our results showed that the concentration of EPFRs reached the maximum at pyrolysis temperature of 300 °C, and EPFRs could significantly inhibit the luminescence of P. phosphoreum. Based on the detection of OH radicals in the aquatic system we used, we speculated that the generation of OH may be a crucial contributor to the toxicity of EPFRs. Our results aid to understand the detailed process on the formation of EPFRs in contaminated soil, as well as the basic biotoxicity data of EPFRs, which will be helpful and essential for their potential environmental risk assessments.

Speciation of Phosphorus Zinc and Copper in Soil and Water-Dispersible Colloid Affected by a Long-Term Application of Swine Manure Compost

The objective of this study was to investigate the concentration and chemical species of Zn, Cu, and P in the bulk soil and water-dispersible colloid (WDC) fraction collected from a field where swine manure (SM) compost has been continually applied for 23 years. A filtration and ultracentrifugation process was used to separate and collect WDC (20-1000 nm) from the soil. The continual application of SM increased soil P from 1.6 to 4.5 g kg^-1, Zn from 109 to 224 mg kg^-1, and Cu from 87 to 95 mg kg^-1 for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg^-1) and Cu (62 mg kg^-1) were highly accumulated and P (25 g kg^-1) was greater than in the bulk soil. According to the result of X-ray absorption spectroscopy (XAS), the continual application of SM compost increased P associated with Fe hydroxides in the soil and WDC fraction. Iron K-edge XAS revealed the dominance of goethite and ferrihydrite in the WDC fraction, suggesting that P was bound to these (oxy)hydroxides. Copper K-edge XAS determined the dominance of Cu(II) associated with humus in the soil and WDC fraction. For Zn species in the SM-compost-applied soil, hopeite and Zn associated with humus were accumulated in the bulk soil, whereas Zn associated with humus was the primary species in the WDC fraction. Our study suggests that the formation of organic complexes in the WDC fraction could enhance the mobility of Zn and Cu as the repeated application of SM compost continues.

Molecular characterization of copper in soils using X-ray absorption spectroscopy

Bioavailability of Cu in the soil is a function of its speciation. In this paper we investigated Cu speciation in six soils using X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and synchrotron-based micro X-ray fluorescence (mu-XRF). The XANES and EXAFS spectra in all of the soils were the same. mu-XRF results indicated that the majority of the Cu particles in the soils were not associated with calcium carbonates, Fe oxides, or Cu sulfates. Principal component analysis and target transform of the XANES and EXAFS spectra suggested that Cu adsorbed on humic acid (HA) was an acceptable match. Thus it appears that Cu in all of the soils is primarily associated with soil organic matter (SOM). Theoretical fitting of the molecular structure in the soil EXAFS spectra revealed that the Cu in the soils existed as Cu atoms bound in a bidentate complex to O or N functional groups.