Speciation and Possible Origins of Organosulfur Compounds in Rice Paddy Soils Affected by Acid Mine Drainage.

Although sulfur cycling in acid mine drainage (AMD)-contaminated rice paddy soils is critical to understanding and mitigating the environmental consequences of AMD, potential sources and transformations of organosulfur compounds in such soils are poorly understood. We used sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy to quantify organosulfur compounds in paddy soils from five AMD-contaminated sites and one AMD-uncontaminated reference site near the Dabaoshan sulfide mining area in South China. We also determined the sulfur stable isotope compositions of water-soluble sulfate (δ34SWS), adsorbed sulfate (δ34SAS), fulvic acid sulfur (δ34SFAS), and humic acid sulfur (δ34SHAS) in these samples. Organosulfate was the dominant functional group in humic acid sulfur (HAS) in both AMD-contaminated (46%) and AMD-uncontaminated paddy soils (42%). Thiol/organic monosulfide contributed a significantly lower proportion of HAS in AMD-contaminated paddy soils (8%) compared to that in AMD-uncontaminated paddy soils (21%). Within contaminated soils, the concentration of thiol/organic monosulfide was positively correlated with cation exchange capacity (CEC), moisture content (MC), and total Fe (TFe). δ34SFAS ranged from -6.3 to 2.7‰, similar to δ34SWS (-6.9 to 8.9‰), indicating that fulvic acid sulfur (FAS) was mainly derived from biogenic S-bearing organic compounds produced by assimilatory sulfate reduction. δ34SHAS (-11.0 to -1.6‰) were more negative compared to δ34SWS, indicating that dissimilatory sulfate reduction and abiotic sulfurization of organic matter were the main processes in the formation of HAS.

Inhibition Effect and Mechanism of Thiourea on Electrophilic Chlorination of Aromatics in Combustion Flue Gas.

Thiourea can effectively inhibit the formation of highly toxic chlorinated aromatics in postcombustion zone. However, the inhibition mechanism was still not adequately understood. In this study, naphthalene was adopted as a model aromatic compound to investigate the inhibition effect and mechanism of thiourea on the formation of chlorinated aromatics via electrophilic chlorination over Cu and Fe chlorides. Thiourea addition resulted in the reductions of 77.6-99.8% and 36.4-98.1% in the yield of polychlorinated naphthalenes from naphthalene chlorination mediated by CuCl2 and FeCl3 at 150-300 °C, respectively. The inhibition efficiency of chlorination presented a decreasing tendency with increasing reaction temperature and O2 content in flue gas. X-ray diffraction analysis revealed that the thiourea-induced reduction of highly active Cu (II) and Fe (III) chlorides to less active Cu (I) and Fe (II) chlorides was a primary mechanism for inhibiting aromatic chlorination. [thiourea-Cu]+ complex generated during the reduction process could be transformed into CuS and Cu2S, and isomeric reaction product NH4SCN could react with Cu2+ to produce Cu(SCN)2 and then also form Cu sulfides, suggesting sulfidization of Cu chloride was another important inhibition mechanism. Chlorination inhibition induced by the volatile decomposition products of thiourea might only play a minor role.

Electrophilic Chlorination of Naphthalene in Combustion Flue Gas.

Naphthalene chlorination is an important formation mechanism of polychlorinated naphthalenes (PCNs) in combustion flue gas. In this study, a total of 21 metal chlorides and oxides were screened for their activities in the electrophilic chlorination of naphthalene. Copper(II) chloride exhibited the highest activity at 200-350 °C, followed by copper(I) chloride. Copper(II) chloride primarily acted as a strong chlorinating agent to facilitate chlorine substitution on naphthalene. Iron (II and III) chlorides were only highly active at 200-250 °C. At 250 °C, the average naphthalene chlorination efficiency over CuCl2·2H2O was 7.5-fold, 30.2-fold and 34.7-fold higher than those over CuCl, FeCl3·6H2O and FeCl2·4H2O, respectively. The other metal chlorides were less active. Under heated conditions, copper(II) and iron(III) chlorides were transformed to copper(I) and iron(II) chlorides via dechlorination, and then transformed to oxychlorides and oxides, thereby forming dechlorination-oxychlorination cycles of copper and iron species, respectively. The results obtained suggest that electrophilic chlorination of naphthalene in combustion flue gas is primarily driven by dechlorination-oxychlorination cycles of copper and iron species, and the reaction produces a selective chlorination pattern at 1 and 4 positions of naphthalene.

Influence of Air Pollution on Inhalation and Dermal Exposure of Human to Organophosphate Flame Retardants: A Case Study During a Prolonged Haze Episode.

The health impact of haze is of great concern, but few studies have explored its influence on human inhalation and dermal exposure to trace pollutants. Size-segregated atmospheric particles ( n = 72) and forehead wipe samples ( n = 80) from undergraduates were collected in Xinxiang, China, during a prolonged haze episode and analyzed for 10 organophosphate flame retardants (OPFRs). ∑TCPP and TCEP were the most abundant OPFR substances in all samples. The arithmetic mean particle-bound and forehead OPFR concentrations under a heavy pollution condition (air quality index (AQI), 350-550) were 41.9 ng/m3 (∑8OPFRs) and 7.4 µg/m2 (∑6OPFRs), respectively, apparently greater than the values observed under a light pollution condition (AQI, 60-90) (19.5 ng/m3 and 3.9 µg/m2, respectively). Meteorological conditions played distinctive roles in affecting the OPFR occurrence in atmospheric particles (statistically significant for TCEP and ∑TCPP) and forehead wipes (excluding TPHP), implying that OPFR exposure through inhalation and dermal absorption was synchronously influenced by air quality, and OPFRs on the forehead may be mainly absorbed from the air. Inhalation contributed dominantly to the total OPFR exposure dose for humans when using the relative absorption method to assess dermal exposure, while according to the permeability coefficient method, dermal exposure was much more significant than inhalation. The results of this study indicate that OPFR exposure should attract particular concern in regions with heavy air pollution.

Influence of tartaric acid on the electron transfer between oxyanions and lepidocrocite.

Iron oxide minerals control the environmental behavior of trace elements. However, the potential effects of electron transfer directions by iron oxides between organic acids and trace elements remain unclear. This study investigates the redox capacity of tartaric acid (TA) with chromate (Cr(Ⅵ)) or arsenate (As(V)) on lepidocrocite (Lep) from the perspective of electron transfer. The results demonstrated the configurations of TA (bidentate binuclear (BB)), As(V) (BB), and Cr(Ⅵ) (BB and protonated monodentate binuclear (HMB)) on Lep. Frontier molecular orbital calculations and X-ray photoelectron spectroscopy (XPS) binding energy shifts further indicated different electron transfer directions between TA and the oxyanions on Lep. The iron of Lep might act as electron acceptors when TA is adsorbed, whereas the iron and oxygen of Lep act as electron donors when As(V) is adsorbed. The iron of Lep might accept electrons from its oxygen and subsequently transfer these electrons to Cr(Ⅵ). Macroscopic validation experiments showed the reduction of Cr(VI), whereas no reduction of As(V). The XPS analysis showed a peak shift, with the possible formation of As-Fe-TA ternary complexes and electron transfer on Lep. These findings indicate that mineral interfacial electron transfer considerably influences the transport and transformation of oxyanions.

Sulfidation of Cd-Sch during the microbial sulfate reduction: Nanoscale redistribution of Cd.

Schwertmannite (Sch) is found in environments abundant in iron and sulfate. Microorganisms that utilize iron or sulfate can induce the phase transition of Schwertmannite, consequently leading to the redistribution of coexisting pollutants. However, the impact of the molar ratio of sulfate to iron (S/Fe) on the microbial-mediated transformation of Schwertmannite and its implications for the fate of cadmium (Cd) have not been elucidated. In this study, we examined how S/Fe influenced mineral transformation and the fate of Cd during microbial reduction of Cd-loaded Schwertmannite by Desulfovibrio vulgaris. Our findings revealed that an increase in the S/Fe ratio facilitated sulfate-reducing bacteria (SRB) in mitigating the toxicity of Cd, thereby expediting the generation of sulfide (S(-II)) and subsequently triggering mineral phase transformation. As the S/Fe ratio increased, the predominant minerals in the system transitioned from prismatic-cluster vivianite to rose-shaped mackinawite. The Cd phase and distribution underwent corresponding alterations. Cd primarily existed in its oxidizable state, with its distribution being directly linked not only to FeS content but also showing a robust correlation with phosphorus. The coexistence of vivianite and FeS minerals proved to be more favorable for Cd immobilization. These findings have significant implications for understanding the biogeochemistry of iron (oxyhydr)oxides and Cd fate in anaerobic environments.

Effect of urea on chlorinated aromatics formation mediated by copper and iron species in combustion flue gas.

Urea ((NH2)2CO) is widely applied to the reduction of NOX in modern full-scale solid waste incineration systems, but there is a lack of knowledge about how urea affects the formation and emission of Cl-aromatics. In this study, we investigated the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated polychlorinated naphthalenes (PCNs) via electrophilic chlorination and precursor pathway mediated by model fly ashes containing Cu and Fe species with or without urea addition. The results indicated that the addition of urea promoted the direct chlorination of parent aromatics over Cu (Ⅱ) chlorides and the coupling reaction of chlorophenols over Fe species, while suppressed the catalytic chlorination of parent aromatics over Fe (Ⅲ) chlorides and the coupling reaction of chlorophenols over Cu species. The diverse effects should be mainly attributed to the formation of complex salts containing NH3 and NH4+. The formation of complex salts of Fe chlorides and NH4Cl could hinder the oxidization of Fe chlorides, and thus maintain the high activity of Fe species for catalyzing the coupling reaction of chlorophenols. The formation of complex salts of Cu (Ⅱ) chloride and NH3 could prevent the chemical sorption of phenoxyl groups, and thus suppress the coupling reaction of chlorophenols. NH3 released from the thermal decomposition of urea could not only react with Cl2 to suppress the catalytic chlorination of aromatics, but also neutralize HCl to accelerate the direct chlorination of aromatics. In general, urea should act as inhibitor for suppressing the formation of Cl-aromatics in solid waste incineration systems.

Suppressing the formation of chlorinated aromatics by inhibitor sodium thiocyanate in solid waste incineration process.

Suppressing the formation of chlorinated aromatics (Cl-aromatics) by chemical inhibitors is an important measure to reduce dioxin emission from the solid waste incineration plants. In this study, we first investigated the reduction effect of a novel inhibitor sodium thiocyanate (NaSCN) on the emission of dioxins in 2 full-scale solid waste incineration systems. Injection of NaSCN solution into the higher temperature flue gas resulted in about 60% reduction in the concentration of total tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans in stack flue gas. The suppression effect was further verified by a laboratory study on the chlorination of naphthalene over model fly ashes with or without NaSCN addition. By characterizing the reaction products between NaSCN and key catalysts Cu and Fe chlorides, two main suppression mechanisms were proposed: (i) reduction of highly active cupric chloride (CuCl2) and ferric chloride (FeCl3) to less active cuprous chloride (CuCl) and ferrous chloride (FeCl2), (ii) sulfidation of Cu chlorides. The laboratory study indicated that the unreacted NaSCN in the combustion flue gas could be mainly decomposed into Na2S, C3N4, Na2S2O3, NaS2, Na2SO4, CO2, SO2, NO2 and COS. These decomposition products are low toxic or can be effectively removed by the air pollution control devices. CAPSULE: NaSCN suppressed the formation of chlorinated aromatics in combustion flue gas mainly through inducing the reduction of highly active Cu (II) and Fe (III) chlorides.

Spraying polyacrylamide solution to improve the removal of particle-phase dioxins by bag filter in a full-scale municipal solid waste incineration system.

A field experiment was conducted in a modern municipal solid waste (MSW) incineration power plant to explore the feasibility of using chemical agglomeration agent anionic polyacrylamide (PAM) to reduce the atmospheric emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Spraying PAM solution into the cooling tower caused an obvious decrease in the volume fraction of ultrafine and fine particles with diameter of 0.3-30 µm in BF fly ash, and a significant reduction in dust content in stack gas. The increased agglomeration of particles promoted the removal of particle-phase PCDD/Fs by BF, and thus resulted in a lower atmospheric emission of PCDD/Fs. The calculated removal efficiency of PCDD/Fs by BF was almost positively proportional to the concentration of PAM solution, while inversely proportional to the average content of dusk in stack gas. Compared with the control treatment, the spraying of 0.1 g/L PAM solution enhanced the removal efficiency of total tetra-to octa-CDD/Fs (∑PCDD/Fs) from 93.8% to 97.8% by BF, and resulted in a decrease of 47.0% in the concentration of international toxicity equivalent (I-TEQ) in stack gas. During the experiment of 2 d, the spraying of PAM solution did not induce a significant change in the differential pressure of BF, and did not essentially affect the partitioning behaviors of PCDD/F homologues between flue gas and BF fly ash. In view of technical safety and low cost, PAM application is recommended for reducing the atmospheric emission of PCDD/Fs from MSW incineration system.

Identifying dust as the dominant source of exposure to heavy metals for residents around battery factories in the Battery Industrial Capital of China.

Heavy metals (HMs) are constantly released into the environment during the production and use of batteries. Battery manufacturing has been ongoing for over six decades in the "Battery Industrial Capital" (located in Xinxiang City) of China, but the potential exposure pathways of residents in this region to HMs remain unclear. To clarify the exposure pathways and health risk of human exposure to HMs, hand wipe samples (n=82) and fingernail samples (n=36) were collected from residents (including young children (0-6 years old), children (7-12 years old) and adults (30-60 years old)) living around battery factories. The total concentrations of the target HMs (Zn, Mn, Cu, Pb, Ni, Cr, Cd, Co) in hand wipes ranged from 133 to 8040 µg/m2, and those in fingernails ranged from 9.7-566 µg/g. HM levels in the hand wipe and fingernail samples both decreased with age, and higher HM levels were observed for males than females. The HM composition profiles in these two matrices represented a high degree of similarity, with Zn as the predominant element, and thus, oral ingestion and dermal exposure via dust were expected to be the most important HM exposure pathways for residents in this region. The non-carcinogenic risks (HQs) from dermal and oral ingestion exposure to Cd, Cr, and Pb were higher than those of the other five elements for all three populations, and the HQderm of Cd for young children was 2.1 (HQoral=0.6). Moreover, the hazard index (HI) values of ∑8HMs for young children (HItotal=5.2, HIoral=2.0, HIdermal=3.2) and children (HItotal=1.6, HIoral=1.3, HIdermal=0.3) exceeded the safe threshold (1.0). Therefore, young children and children should be prioritized for protection from HM pollution, and more attention should be paid to young children's dermal exposure to Cd in this region.

Electrophilic chlorination of dibenzo-p-dioxin and dibenzofuran over composite copper and iron chlorides and oxides in combustion flue gas.

Dibenzo-p-dioxin (DD) and dibenzofuran (DF) chlorination mediated by Cu and Fe chlorides can make a direct contribution to the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in combustion flue gas. In this study, a kind of composite Cu and Fe chlorides and oxides (CuFe9O9.5Cl10) was prepared by impregnating oxides with HCl solution to imitate the coexistence status of Cu and Fe species in combustion flue gas. Composite CuFe9O9.5Cl10 was active in promoting the electrophilic chlorination of DD/DF at 150-300 °C, with the highest activity at 200 °C. DD/DF chlorination could occur under inert atmosphere, and 5% O2 atmosphere was most favorable for DD/DF chlorination. Electrophilic chlorination of DD/DF primarily favored at 2,3,7,8 positions. Hybridization of Cu and Fe chlorides and oxides not only decreased the starting temperature and activation energy of DD/DF chlorination, but also induced a synergistic effect for accelerating the chlorination of DD/DF. The measured activities of composite CuFe9O9.5Cl10 for promoting the chlorination of DD/DF were near to those of composite Cu chloride and oxide (CuO0.2Cl1.6), whereas 2 orders of magnitude higher than those of composite Fe chloride and oxide (FeO0.3Cl2.4). Comparison of PCDD/F congener distribution patterns indicated that DD/DF chlorination should be a main source of Cl1-3DFs and Cl1-2DDs in combustion flue gases.

Partitioning and removal behaviors of PCDD/Fs, PCBs and PCNs in a modern municipal solid waste incineration system.

An extensive evaluation on a modern full-scale municipal solid waste incineration system was conducted for characterizing the distribution of highly toxic chlorinated aromatics, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs), and their corresponding mass fluxes in post combustion zone. It was found that the flue gas/fly ash partitioning behaviors of chlorinated aromatics could be essentially described by their octanol-air partition coefficients (KOA) and strongly affected by the flue gas temperature. Above 93% of chlorinated aromatics formed in boiler section was partitioned into the flue gas and transported into the subsequent flue gas cleaning system, in which above 92% of Cl3-8DDs, Cl3-7DFs, Cl5-10Bs and Cl4-8Ns in flue gas was removed by the discharge of fly ash. The results of mass flux calculation indicated that the memory effect in flue gas cleaning system remarkably elevated the emission levels of chlorinated aromatics, especially the less chlorinated ones. The memory effect should mainly result from the direct chlorination mechanism mediated by the deposited particles. In addition, activated carbon injection could cause an obvious increase in PCBs emission. The obtained results provided some important implications for further reducing the emission of highly toxic chlorinated aromatics.

The non-negligible environmental risk of recycling halogenated flame retardants associated with plastic regeneration in China.

To investigate halogenated flame retardant (HFR) contents in recycled plastic materials, 23 recycled plastic samples manufactured in five Chinese provinces were randomly purchased online, and the ∑12HFR concentrations of these samples (including 8 polybrominated diphenyl ethers (PBDEs, BDE 28, 47, 99, 100, 154, 153, 183 and 209), decabromodiphenylethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), and 2 dechlorane plus isomers (DP, syn-DP and anti-DP)) varied from ND to 169,000 ng g-1 (mean ±â€¯SD, 46,900 ±â€¯44,700 ng g-1). BDE 209 and DBDPE were the dominant components and their concentration ranges were from ND to 106,000 ng g-1 and ND to 81,900 ng g-1, respectively. Generally, the HFR content and plastic variety closely correlate, and the ∑HFR concentrations in the polyvinyl chloride (PVC, N = 5), polypropylene (PP, N = 9), acrylonitrile butadiene styrene (ABS, N = 5), polystyrene (PS, N = 1) and polyethylene (PE, N = 3) samples were 65,300 ±â€¯42,400, 36,700 ±â€¯56,000, 30,000 ±â€¯25,200, 24,300 and 4330 ±â€¯7500 ng g-1, respectively. The HFR abundance in plastic from Guangdong (76,000 ±â€¯56,400 ng g-1, N = 7) and Hebei (37,500 ±â€¯11,500 ng g-1, N = 4) was much higher than that for other provinces/cities.

Levels and fingerprints of chlorinated aromatic hydrocarbons in fly ashes from the typical industrial thermal processes: Implication for the co-formation mechanism.

Municipal solid waste incineration (MSWI) and iron and steel making plants are two of important sources of chlorinated aromatic hydrocarbons (CAHs). In this study, the typical CAHs including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs) and chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in fly ash samples collected from MSWI, iron ore sintering (IOS) and steel smelting (SS) plants were simultaneously identified and quantified. The total concentrations of quantified CAHs in different fly ashes showed a large variation (5.88-4255 ng/g). Cl-PAHs were found to be predominant CAH species in most of fly ash samples, and the concentrations of mono-chlorinated PAHs in all fly ashes were obviously higher than those of di-chlorinated PAHs. The fingerprints of CAHs in MSWI fly ashes were mainly characterized by the high content of PCDDs, especially the hexa-CDD homologue. However, in IOS and SS fly ashes, tetra- to hexa-CDF homologues showed the higher abundance, and tetra-to octa-CDFs predominated over tetra- to octa-CDDs by factors of 3-26. The strong concentration correlations were observed between tetra- to octa-CDF homologues, middle-chlorinated PCN and PCB homologues, between tetra- to octa-CDD homologues, between low-chlorinated PCB and PCN homologues, between di-chlorinated PAH homologues, and between deca-CB and highly chlorinated PCN homologues. These results implied that the main formation mechanism of CAHs might be significantly varied with the change of chlorination degree and aromatic ring structure.

[Simultaneous Removal of Polychlorinated Dibenzo-p-dioxins/dibenzofurans, Polychlorinated Biphenyls, and Polychlorinated Naphthalenes From Flues Gases From Coke Gas Burning Using Selective Catalytic Reduction Equipment].

The removal efficiencies of typical unintentionally produced persistent organic pollutants (UP-POPs) from flues gases from coke gas burning were obtained using selective catalytic reduction (SCR) equipment installed in a large coking plant. The total congeners of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) in the flue gases at the inlet and outlet of the SCR equipment and the dustfall were analyzed. The results show that the removal efficiency of the total PCDD/Fs was the highest (94.6%). The removal efficiencies of total PCBs and total PCNs were 74.7% and 78.4%, respectively. The homologue profile of UP-POPs in the flue gases at the inlet of the SCR equipment notably differed from that at the outlet. Highly chlorinated UP-POPs predominated over the homologue profile of UP-POPs in the inlet flue gas, while low-chlorinated UP-POPs were predominant in the outlet flue gas. The SCR equipment achieved a better removal efficiency with respect to highly chlorinated UP-POPs. Catalytic reduction and catalytic oxidation degradation are both important mechanisms for the removal of UP-POPs from flue gas using SCR equipment.

Higher health risk resulted from dermal exposure to PCBs than HFRs and the influence of haze.

To investigate the influence of haze on human dermal exposure to a series of halogenated flame retardants (HFRs) and polychlorinated biphenyls (PCBs), paired forehead wipes were collected from 46 volunteers (23 males, 23 females) using gauze pads soaked in isopropyl alcohol under heavy and light haze pollution levels. The median levels of ∑27HFRs and ∑27PCBs in all 92 samples were 672 and 1300ng/m2, respectively. Decabromodiphenyl ether (BDE-209) (171ng/m2) and decabromodiphenylethane (DBDPE) (134ng/m2) were the dominant components of HFRs, indicating that dermal exposure may also be the significant pathway for non-volatile compounds. PCB-37 contributed the most to ∑27PCBs, with a median concentration of 194ng/m2, followed by PCB-60 (141ng/m2). Generally, PBDE, PCB and DD (dehalogenated derivatives of DPs) levels on the foreheads of female participants (291, 1340, 0.92ng/m2) were higher (p=0.037, 0.001, and 0.031, respectively) than those of male participants (226, 989, and 0.45ng/m2). A significant difference (p=0.001) in PCBs was found between light (1690ng/m2) and heavy (996ng/m2) haze pollution conditions. Nevertheless, HFR levels under heavy (median=595ng/m2, ranging from 295 to 1490ng/m2) and light haze pollution conditions (ranging from 205 to 1220ng/m2 with a median of 689ng/m2) did not show significant differences (p=0.269). The non-carcinogenic health risk resulting from dermal exposure to ∑8HFRs and ∑27PCBs was 8.72×10-5 and 1.63×10-2, respectively, raising more concern about populations' exposure to PCBs than HFRs.