Profiles, sources, and transport of polycyclic aromatic hydrocarbons in soils affected by electronic waste recycling in Longtang, south China.

We studied the profiles, possible sources, and transport of polycyclic aromatic hydrocarbons (PAHs) in soils from the Longtang area, which is an electronic waste (e-waste) recycling center in south China. The sum of 16 PAH concentrations ranged from 25 to 4,300 ng/g (dry weight basis) in the following order: pond sediment sites (77 ng/g), vegetable fields (129 ng/g), paddy fields (180 ng/g), wastelands (258 ng/g), dismantling sites (678 ng/g), and former open burning sites (2,340 ng/g). Naphthalene, phenanthrene, fluoranthene, pyrene, chrysene, and benzo[b]fluoranthene were the dominant PAHs and accounted for approximately 75 % of the total PAHs. The similar composition characteristics of PAHs and the significant correlations among individual, low molecular weight, high molecular weight, and total PAHs were found in all six sampling site types, thus indicating that PAHs originated from similar sources. The results of both isomeric ratios and principal component analyses confirmed that PAHs were mainly derived from the incomplete combustion of e-waste. The former open burning sites and dismantling sites were the main sources of PAHs. Soil samples that were taken closer to the point sources had high PAH concentrations. PAHs are transported via different soil profiles, including those in agricultural fields, and have been detected not only in 0- to 40-cm-deep soil but also in 40 cm to 80 cm-deep soil. PAH concentrations in soils in Longtang have been strongly affected by primitive e-waste recycling, particularly by former open burning activities.

Heterogeneous photodegradation of pentachlorophenol and iron cycling with goethite, hematite and oxalate under UVA illumination.

Heterogeneous photodegradation of pentachlorophenol (PCP) in the goethite (alpha-FeOOH) and hematite (alpha-Fe(2)O(3)) systems with oxalate under UVA illumination was investigated. The PCP degradation, dechlorination and detoxification, in terms of Microtox acute toxicity, were all achieved to the higher efficiency in the hematite suspension than in the goethite suspension. The optimal initial concentration of oxalic acid (C(ox)(0)) for the PCP degradation with goethite and hematite under the experimental conditions was found to be 1.2mM, since sufficient Fe(III) as Fe(C(2)O(4))(3)(3-) and Fe(II) as Fe(C(2)O(4))(2)(2-) can be formed at C(ox)(0)>or=1.2mM. The main intermediates of PCP degradation were identified by GC-MS, HPLC and IC analyses. It was found that the cycling process between Fe(III) and Fe(II) in both the goethite and hematite systems occurred more vigorously at the initial stage and gradually became gentle, while the rate of PCP photodegradation varied from fast to slow during the reaction time. Furthermore, the formation of H(2)O(2) during photoreaction was studied to explore its relationship with the photodegradation efficiency and the iron cycling process.

The oxidative transformation of sodium arsenite at the interface of alpha-MnO2 and water.

Arsenite is acute contaminant to human health in soil and water environment. In this study, Pyrolusite (alpha-MnO(2)) was used to investigate the oxidative transformation of arsenite into arsenate with batch experiments under different reaction conditions. The results showed that arsenite transformation occurred and was accompanied by the adsorption and fixation of both As(III) and As(V) on alpha-MnO(2). About 90% of sodium arsenite (10mg/L) were transformed by alpha-MnO(2) under the conditions of 25 degrees C and pH 6.0, 36.6% of which was adsorbed and 28.9% fixed by alpha-MnO(2). Increased alpha-MnO(2) dosages promoted As (III) transformation rate and adsorption of arsenic species. The transformation rate and adsorption of arsenic species raised with increasing pH values of reaction solution from 4.7 to 8.0. The oxidation rate decreased and adsorbed As(III) and As(V) increased with increasing initial arsenite concentration. The enhancement on oxidative transformation of sodium arsenite may result from abundant active sites of alpha-MnO(2). Along with adsorption and fixation of arsenic species during the reaction, the crystal structure of alpha-MnO(2) did not change, but the surface turned petty and loosen. Our results demonstrated that alpha-MnO(2) has important potential in arsenic transformation and removal as the environmentally friendly natural oxidant in soil and surface water.

Dependence of bisphenol A photodegradation on the initial concentration of oxalate in the lepidocrocite-oxalate complex system.

To understand the degradation of endocrine disrupting chemicals (EDCs) in natural environment with existence of iron oxides and carboxylic acids, the dependence of bisphenol A (BPA) photodegradation on the initial concentration of oxalate (COX) in lepidocrocite (gamma-FeOOH) aqueous suspension was investigated under both UV and visible lights in this study. Lepidocrocite powder was home-prepared by a hydrothermal process. It was found that BPA degradation was promoted greatly in the presence of oxalate owing to the formation of lepidocrocite-oxalate complex. And there was an optimal COX, which was 2.0 and 2.4 mmol/L, under UV and visible lights, respectively. The first-order kinetic constant, k value increased 38 times from 0.17 x 10(-2) min(-1) in the absence of oxalate to 6.39 x 10(-2) min(-1) in the presence of oxalate with an optimal COX (2.0 mmol/L) under UV irradiation, and almost 306 times from 0.02 x 10(-2) min(-1) in the absence of oxalate to 6.11 x 10(-2) min(-1) in the presence of oxalate with an optimal COX (2.4 mmol/L) under visible irradiation. The BPA degradation rate increased and the first-order kinetic constants decreased with the increase in BPA initial concentration. The dependence of the variation of pH value, total-Fe and Fe2+ during the photoreaction on COX was also investigated. The pH value increased obviously with the reaction time. Total-Fe increased dramatically at the first 5 min and then decreased quickly under UV irradiation and slowly under visible irradiation. The initial concentration of oxalate is a main factor to affect BPA photodegradation in aqueous suspension under both UV and visible lights.

The effect of erbium on the adsorption and photodegradation of orange I in aqueous Er3+-TiO2 suspension.

Pure TiO(2) and erbium ion-doped TiO(2) (Er(3+)-TiO(2)) catalysts prepared by the sol-gel method were characterized by means of XRD and diffusive reflectance spectra (DRS). The XRD results showed that erbium ion doping could enhance the thermal stability of TiO(2) and inhibit the increase of the crystallite size, and the DRS results showed that the optical absorption edge slightly shifted to red direction owing to erbium ion doping and the Er(3+)-TiO(2) catalysts had three typical absorption peaks located at 490, 523 and 654 nm owing to the transition of 4f electron from (4)I(15/2) to (4)F(7/2), (2)H(11/2) and (4)F(9/2). With a purpose of azo dyes degradation, orange I was used as a model chemical. And the adsorption isotherm, degradation and mineralization of orange I were investigated in aqueous suspension of pure TiO(2) or Er(3+)-TiO(2) catalysts. The results showed that Er(3+)-TiO(2) catalysts had higher adsorption equilibrium constants and better adsorption capacity than pure TiO(2). The adsorption equilibrium constants (K(a)) of Er(3+)-TiO(2) catalysts were about twice of that of pure TiO(2). The maximum adsorption capacity (Q(max)) of 2.0% Er(3+)-TiO(2) catalyst was 13.08x10(-5)mol/g, which was much higher than that of pure TiO(2) with 9.03x10(-5)mol/g. Among Er(3+)-TiO(2) catalysts, 2.0% Er(3+)-TiO(2) catalyst achieved the highest Q(max) and K(a) values. The kinetics of the orange I degradation using different Er(3+)-TiO(2) catalysts were also studied. The results demonstrated that the degradation and mineralization of orange I under both UV radiation and visible light were more efficient with Er(3+)-TiO(2) catalyst than with pure TiO(2), and an optimal dosage of erbium ion at 1.5% achieved the highest degradation rate. The higher photoactivity under visible light might be attributable to the transitions of 4f electrons of Er(3+) and red shifts of the optical absorption edge of TiO(2) by erbium ion doping.