Abandoned chemical smelting sites containing toxic substances can seriously threaten and pose a risk to the surrounding ecological environment. Soil samples were collected from different depths (0 to 13 m) and analyzed for metal(loid)s content and fractionation, as well as microbial activities. The potential ecological risk indices for the different soil depths (ordered from high to low) were: 1 m (D-1) > surface (S-0) > 5 m (D-5) > 13 m (D-13) > 9 m (D-9), ranging between 1840.65–13,089.62, and representing extremely high environmental risks, of which Cd (and probably not arsenic) contributed to the highest environmental risk. A modified combined pollution risk index (MCR) combining total content and mobile proportion of metal(loid)s, and relative toxicities, was used to evaluate the degree of contamination and potential environmental risks. For the near-surface samples (S-0 and d-1 layers), the MCR considered that As, Cd, Pb, Sb, and Zn achieved high and alarming degrees of contamination, whereas Fe, Mn, and Ti were negligible or low to moderate pollution degrees. Combined microcalorimetry and enzymatic activity measurements of contaminated soil samples were used to assess the microbial metabolic activity characteristics. Correlation analysis elucidated the relationship between metal(loid)s exchangeable fraction or content and microbial activity characteristics (p < 0.05). The microbial metabolic activity in the d-1 layer was low presumably due to heavy metal stress. Enzyme activity indicators and microcalorimetric growth rate (k) measurements were considered sensitive indicators to reflect the soil microbial activities in abandoned chemical smelting sites.

Many non-ferrous metal mining and smelting activities have caused severe metal(loid) contamination in the local soil environment. The metabolic activity of soil microorganisms in four areas affected by different metallurgical activities (production vs. waste disposal) was characterized using a contamination gradient from the contaminated site to the surrounding soils. Results indicated that the soil microcalorimetric and enzyme activities were correlated with the fractionated metal(loid) properties (p < 0.05). All four areas had high total As, Cd, Pb, Sb, and Zn concentrations, of which mobile As, Cu, Ni, Pb, Sb, and Zn were higher in the contaminated sites than the surrounding sites, reflecting an elevated environmental risk. Three contaminated site areas had lower microbial activities than their surrounding sites suggesting that high metal(loid) concentrations inhibited soil microbial communities. Interestingly, the fourth area (tailing pond) showed an opposite trend (i.e., increased microbial activity in contaminated vs. surrounding areas). The microbial thermodynamic parameters of this contaminated site were higher than its surrounding sites, suggesting that the selected microbial communities can develop a functional resistance to metal(loid)s stress. This study provides a theoretical basis for ecological prevention and control of metal-polluted areas.

Compound specific isotope analysis (CSIA) has been used to explore the degradation pathways of di-(2-ethylhexyl)phthalate (DEHP) in photosensitization experiments with H2O2, TiO2, Fe(III) and PMS. The reaction kinetics could be described by first order rate constants [k (h(-1))]. The highest degradation rates of DEHP were observed in UV/TiO2 catalyzed reactions. Carbon isotope fractionation factors (epsilon(C)) and metabolite patterns were examined to analyze the radical reaction. Similar carbon isotope fractionation factors have been found in experiments dominated by center dot OH radical reactions (UV/H2O2, 1.2 +/- 0.3 parts per thousand; UV/TiO2, 1.2 +/- 0.5 parts per thousand). An inverse carbon isotope fractionation has been found for UV/Fe(III) (0.8 +/- 0.2 parts per thousand) and SO4 center dot- (0.6 +/- 0.2 parts per thousand at pH 3) catalyzed reactions indicating that these reactions preferentially taking place at the H atom bond at tert-butyl carbon of the side chain. This hypothesis is further supported by an experiment with isobutyl acetate (epsilon(C) = 1.8 +/- 0.2 parts per thousand for UV/Fe(III) at pH 7; epsilon(C) = -1.1 +/- 0.2 parts per thousand for UV/PMS at pH 6 and epsilon(C) = 0.9 +/- 0.3 parts per thousand for UV/PMS at pH 3). Quenching experiments in the UV/PMS catalyzed reaction indicated a coexistence of SO4 center dot- and center dot OH at pH 7. SO4 center dot- was the predominant radical at pH 3. (OH)-O-center dot was found to be the predominant radical in UV/H2O2 and UV/ TiO2 reactions. CSIA indicated that the addition of (OH)-O-center dot to the aromatic ring of DEHP by the RAF pathway is the main reaction mechanism in UV/H2O2 and UV/TiO2 experiments. The SO4 center dot- attacks preferentially the C-H bond at the tert-butyl carbon position of the side chain of DEHP which causes an inverse carbon isotope effect. Thus, carbon isotope enrichment factors can be used to distinguish different radical reaction mechanisms with DEHP as a substrate.

The hydrogen and carbon isotope fractionation factor (82H, 813C) of dimethyl-, diethyl-and dibutyl phthalic acid ester during photosensitized degradation by artificial sunlight with Fe(III) ions and iron minerals (hematite, goethite and magnetite) in aqueous solution were examined by compound-specific isotope analysis (CSIA) in order to analyze the degradation mechanism. Hematite does not catalyze photosensitized degradation of phthalates. The correlation of 2H and 13C isotope fractionation (A = A82H/A813C) of phthalates with increasing chain length (dimethyl-; diethyl-; and dibutyl-) were compared with values of the center dot OH radical model reaction with the aromatic ring as well as acidic and alkaline hydrolysis. The A values of die photosensitized reaction of diethyl phthalate with goethite (-5.1 +/- 1.8) and magnetite (-18.9 +/- 3.9) show a large difference compared to Fe (III) solutions (4.7 +/- 0.9 to 4.8 +/- 1.0) suggesting specific reaction mechanisms. The fractionation factors determined here have potential to characterize the degradation of phthalates catalyzed by photo-induced re-action of Fe(III), goethite and magnetite in natural system and in remediation approaches.

The photosensitized transformation of organic chemicals is an important degradation mechanism in natural surface waters, aerosols, and water films on surfaces. Dissolved organic matter including humic-like substances (HS), acting as photosensitizers that participate in electron transfer reactions, can generate a variety of reactive species, such as OH radicals and excited triplet-state HS (3HS*), which promote the degradation of organic compounds. We use phthalate esters, which are important contaminants found in wastewaters, landfills, soils, rivers, lakes, groundwaters, and mine tailings. We use phthalate esters as probes to study the reactivity of HS irradiated with artificial sunlight. Phthalate esters with different side-chain lengths were used as probes for elucidation of reaction mechanisms using 2H and 13C isotope fractionation. Reference experiments with the artificial photosensitizers 4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein (Rose Bengal), 3-methoxy-acetophenone (3-MAP), and 4-methoxybenzaldehyde (4-MBA) yielded characteristic fractionation factors (−4 ± 1, −4 ± 2, and −4 ± 1‰ for 2H; 0.7 ± 0.2, 1.0 ± 0.4, and 0.8 ± 0.2‰ for 13C), allowing interpretation of reaction mechanisms of humic substances with phthalate esters. The correlation of 2H and 13C fractions can be used diagnostically to determine photosensitized reactions in the environment and to differentiate among biodegradation, hydrolysis, and photosensitized HS reaction.

Mining and smelting activities have brought potentially serious heavy metal(loid)s pollution to their surrounding locale. However, studies on microbial metabolic activities, community structure, and adaptation in soils proximal to non-ferrous metal mining and smelting areas are still lacking. Here the effects of biotic and abiotic characteristics of soil taken from sites surrounding inactive and active non-ferrous metal mine smelting facilities on microbial enzyme activity, microcalorimetry, and high-throughput sequencing of 16S rRNA gene barcoding were studied. Data indicated that the soils were heavily polluted by toxic metal(loid)s, of which As and Cd were the main contaminants. Microbial acid phosphatase activity and microcalorimetric total heat value were sensitive metabolic indicators in the studied areas. Actinobacteriota had the highest relative abundance, followed by Proteobacteria, Chloroflexi, and Acidobacteria. Microbial metabolic activity, bacterial community structure and phenotype varied between inactive and active sites (p < 0.05). Such analyses indicated that electrical conductivity, total As, Cu, and Mn contents, and bioavailable As, Cu, Cd, and Mn concentrations were key factors determining microbial activities, bacterial community structure, and phenotypes. Knowledge of microbial adaptation to heavy metal stressors is important for better understanding the aerial transfer of fugitive heavy metal(loid)s (and possibly microbes) and for designing future strategies for improved soil bioremediation.

In this study compound-specific isotope analysis (CSIA) has been used to explore the degradation mechanism of nano titanium dioxide (TiO2) catalyzes photodegradation of diethyl phthalate (DEP). TiO2 is a popular photosensitizer with potential in waste water treatment and application in advanced oxidation processes. The degradation process of DEP can be described with a first-order kinetics in the applied concentration ranges. The larger degradation rate constant has been found at neutral conditions. The 13C and 2H isotope fractionation associated with the nano TiO2 catalyzes photodegradation of DEP at pH 3, 7 and 11 yield normal isotope effects. In the TiO2/UV/DEP and TiO2/H2O2/UV/DEP systems, the correlation of 13C and 2H fractionation (Λ) were calculated to be 2.7 ± 0.2, 2.8 ± 0.2 at pH 3, 2.2 ± 0.4, 2.5 ± 0.2, 2.3 ± 0.6 at pH 7 and 2.6 ± 0.3, 2.2 ± 0.3, 2.7 ± 0.2 and 2.3 ± 0.3 at pH11, respectively. The dominant free radical species in studied systems were explored by combining free radical quenching method and electron paramagnetic resonance analysis. The hydroxyl radicals have been found as the main radical species at all pH conditions studied. Furthermore, the 13C and 2H fractionation suggested that the addition of •OH on the benzene ring of DEP is the main conversion pathway. Therefore, CSIA is a promising technology for the identification of reaction pathways of DEP for example in water treatment systems.

This study reports the C-13 and H-2 isotope fractionation associated with the oxidation of diethyl phthalate (DEP) by persulfate (PS) activated with zero-valent iron (ZVI) using three concentration levels (0.2, 0.5 and 1.0 g L-1) at different pH values, 3, 7 and 11, respectively. The results showed that the degradation of DEP followed a pseudo first-order kinetics. The fastest degradation was found at neutral conditions (pH 7). Similar carbon and hydrogen isotope fractionation (epsilon(C) and epsilon(H)) was observed during the oxidation of DEP by ZVI activated PS at pH 3, 7 and 11. At ZVI concentration of 0.5 g L-1, the correlation of C-13 and H-2 fractionation (A) were obtained to be 12.7 & PLUSMN; 3.5, 11.1 & PLUSMN; 4.2 and 12.0 & PLUSMN; 2.9 at pH 3, 7 and 11, respectively. The concentration of ZVI has no effect on the correlation of C-13 and H-2 fractionation (A). In addition, radical quenching approach and electron paramagnetic resonance (EPR) were combined to explore the dominant radical species in the ZVI activated PS reaction, and hydroxyl radical (& BULL;OH) was found to be the predominant radical at all pH studied. The results of CSIA show the addition of & BULL;OH to the aromatic ring of DEP is the main reaction mechanism, which is consistent with the results of radical quenching experiment and EPR study. Carbon and hydrogen apparent kinetic isotope effects (AKIEs) obtained from & BULL;OH reactions with DEP supported the hypothesis of C-H bond cleavage. Thus, carbon and hydrogen isotope enrichment factors clearly distinguish the different reaction mechanisms and hence, are a promising approach to improve understanding of radical species reaction pathways for chemical oxidation of DEP.

Here we combined microcalorimetry, enzyme activity measurements, and characterization of metal form in order to evaluate the effect of metal(loid)s on the activity of microbial community inhabiting tailings area with high toxic metal(loid)s concentration. Chromium (Cr), nickel (Ni), copper (Cu) and manganese (Mn) were the main pollutants. The exchangeable fractions (bioavailability) of Cu, Ni and Mn were higher in the tailings sample (Site Z), indicating a higher environmental risk. The total heat Qtotal (17,726.87 J/g), peak power Ppeak(541.42 mu W/g) and growth rate constant k (0.11 h-1) of Site Z were higher than that of the polluted soil around tailings (Site Y). Such observation may be explained by physiological changes within the microbial community in response to high levels of heavy metal stress, thereby increasing respiration and improving microbial activity. In contrast, enzyme activities and enzyme activities index (GmeA) of Site Z were lower than the Site Y, which is strongly influenced by changes on physical-chemical properties (TN and TOC) and the presence of Cr, Mn, and Ni. Correlation coefficient and principal component analysis (PCA) indicate that GmeA is significantly correlated (p < 0.05 or p < 0.01) with environmental factors (EC, TOC and TN), Mn and Ni concentration, Ni bioavailability, and peak time (Tpeak). Therefore, GmeA represents a potential biological indicator for reporting the pollution degree in tailings area. Our results provide a theoretical basis for the prevention and control of pollution in non-ferrous metal(loid) tailings area.

Butyl Xanthate (BX) is a typical flotation reagent used to extract non-ferrous nickel ores, discharged into the surrounding environment of mining areas in large quantities. However, few studies have focused on the toxicity of combined pollution of BX and nickel (Ni) on aquatic plants, especially phytoplankton, the main producer of aquatic ecosystems. The toxicity and potential mechanism of single and combined pollution of BX and Ni at different concentrations (0-20 mg L-1) on typical freshwater algae (Chlorella pyrenoidosa) were studied. BX slightly stimulated the growth of C. pyrenoidosa on the first day, but Ni and Ni/BX mixture significantly inhibited it during incubation. Results showed that the inhibition rate (I) of the pollutants on the growth of C. pyrenoidosa followed the order: Ni/BX mixture > Ni > BX. The 96-h 20% effective inhibitory concentrations (96h-EC20) of Ni and BX on C. pyrenoidosa growth were 3.86 mg L-1 and 19.25 mg L-1, respectively, indicating C. pyrenoidosa was sensitive to pollutants. The content of total soluble protein (TSP) and chlorophyll a (Chl-a) changed significantly, which may be caused by the damage of pollutants to cell structures (cell membranes and chloroplasts). In addition, the I of pollutants on C. pyrenoidosa growth was related to dose, superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA). The increasement of reactive oxygen species (ROS), antioxidant enzymes (SOD and CAT), and MDA content, suggested C. pyrenoidosa suffered from oxidative stress, leading to lipid oxidation. These results will help to understand the toxicity mechanism of pollutants in typical mining areas and assess the environmental risks of pollutants to primary producers in aquatic ecosystems.

Compound-specific isotope analysis (CSIA) is a useful technique that has received an increasing attention for studying the degradation mechanisms of organic contaminants based on stable isotope fractionation concepts. This study reports the degradation mechanisms of p-chloroaniline (PCA) at different pH values (3, 5, 7 and 9) induced by persulfate (PS) based on 13C isotope fractionation during its preferential oxidation with SO4 center dot- and center dot OH. The results showed that the degradation of PCA followed first-order kinetics (rate constants, 0.026, 0.0362, 0.0754 and 0.0497 h-1 at pH = 3, 5, 7 and 9, respectively), with the fastest degradation under neutral conditions (pH 7). The degradation rate was found to be higher under alkaline conditions (pH 9) compared to acidic conditions (pH 3 and 5). A normal carbon isotope fractionation of PAC was observed under neutral and alkaline conditions (eg., epsilon C = -0.8%o +/- 0.10 at pH 7 and epsilon C = -1.0%o +/- 0.17 at pH 9). However, a reverse carbon isotope effect at pH 3 (epsilon C = 0.6%o +/- 0.07) and pH 5 (epsilon C = 1.1%o +/- 0.06) was observed, respectively. Based on the identified transformation products and the insights revealed by CSIA, the degradation pathways were proposed. The current findings are crucial in understanding the PCA degradation mechanisms with SO4 center dot- and center dot OH in aqueous systems.

A reliable, simple and fast method was developed to detect four phthalic acid esters (PAEs) including dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP) and diethylhexyl phthalate (DEHP) in mine tailings based on the accelerated solvent extraction (ASE) combined with gas chromatography-mass spectrometry (ASE/GC-MS). Evaluation of extraction parameters including choice of extraction solvent, temperature, extraction time, and number of extraction cycles showed that dichloromethane, 120 degrees C, 3 min, and 2 cycles were optimal, respectively. Under these conditions, the limit of detection (LOD) and limit of quantitation (LOQ) values were in the range of 1.2-2.0 mu g kg(-1) and 3.0-4.6 mu g kg(-1), respectively, and precision of the analytical data, RSD <= 7.0% were determined. This method was used to analyze the PAEs-spiked mine tailing samples (100 mu g kg(-1) of each analyte). Acceptable recovery values of 71.3-77.1%, 100-110%, 105-116%, and 101-115% were obtained for DMP, DEP, DBP and DEHP, respectively. The technique was also successfully applied for the extraction of the PAEs in real samples collected from mine tailing pond. Finally, stable C and H isotope analyses were conducted using GC coupled to isotope ratio MS to investigate effect of the ASE method on H and C isotopic compositions of the target analytes. Results showed that the ASE procedure did not lead to significant isotope fractionation of the compounds. Overall, the major advantages of this method are: automated operation, high sensitivity, short extraction time, less solvent consumption, and compatibility with a variety of detecting equipment. Combined with CSIA, it could be used to study the degradation mechanisms of target PAEs in mine tailing environments.

The combined toxicological effects of nickel (Ni) and butyl xanthate (BX), that is commonly used in flotation reagents for non-ferrous metals ore processing such as Ni, copper and lead ores, on soil microbial communities were studied by determining soil microbial activity, soil enzyme activities and Ni bioavailability. The results revealed that the exchangeable (EXC) and reducible (RED) fractions of Ni were higher in Ni/BX mixture than Ni alone, probably because BX reacts with Ni to form complexes that lead an increase in bioavailability of Ni. The presence of BX and Ni inhibited microbial activity and enzyme activities during the first 30-days. Then, from 30 days to 180 days, different trends were observed according to the condition: microbial activity was stimulated with BX alone while it was inhibited with Ni/BX mixture. This observation was supported by the fact that the inhibitory ratio (I) was higher for Ni/BX mixture than BX alone. Results showed that the sensitivity to one or both contaminants followed the order: urease (UA) > invertase (INV). EXC fraction of Ni/BX mixture were significantly correlated with UA, INV, I, peak power (Ppeak) and peak time (Tpeak), respectively (p < 0.01), suggesting that Ni bioavailability might explain the Ni toxicity against microbial communities under combined pollution conditions. Such observations allow us to better understand toxic effects of Ni pollution when accompanied with BX, facilitating precisely evaluation of potential risks in mining areas.

Abandoned nonferrous metal(loid) tailings sites are anthropogenic, and represent unique and extreme ecological niches for microbial communities. Tailings contain elevated and toxic content of metal(loid)s that had negative effects on local human health and regional ecosystems. Microbial communities in these typical tailings undergoing natural attenuation are often very poorly examined. The diversity and inferred functions of bacterial communities were examined at seven nonferrous metal(loid) tailings sites in Guangxi (China), which were abandoned between 3 and 31 years ago. The acidity of the tailings sites rose over 31 years of site inactivity. Desulfurivibrio, which were always coupled with sulfur/sulfide oxidation to dissimilate the reduction of nitrate/nitrite, were specific in tailings with 3 years abandonment. However, genus beneficial to plant growth (Rhizobium), and iron/sulfur-oxidizing bacteria and metal(loid)-related genera (Acidiferrobacter and Acidithiobacillus) were specific within tailings abandoned for 23 years or more. The increased abundance of acid-generating iron/sulfur-oxidizing and metal(loid)-related bacteria and specific bacterial communities during the natural attenuation could provide new insights for understanding microbial ecosystem functioning in mine tailings. OTUs related to Sulfuriferula, Bacillus, Sulfurifustis, Gaiella, and Thiobacillus genera were the main contributors differentiating the bacterial communities between the different tailing sites. Multiple correlation analyses between bacterial communities and geochemical parameters indicated that pH, TOC, TN, As, Pb, and Cu were the main drivers influencing the bacterial community structures. PICRUSt functional exploration revealed that the main functions were related to DNA repair and recombination, important functions for bacterial adaptation to cope with the multi-contamination of tailings. Such information provides new insights to guide future metagenomic studies for the identification of key functions beyond metal-transformation/resistance. As well, our results offers novel outlooks for the management of bacterial communities during natural attenuation of multi-contaminated nonferrous metal(loid) tailings sites.

In non-ferrous metal tailings, combined pollution in the surrounding soil is caused by heavy metals and flotation chemicals. The combined effects of nickel (Ni) and its primary ore processing collector, sodium butyl xanthate (SBX), on soil microbial activity were investigated following the fluorescein diacetate hydrolase (FDA) and sucrase (SA) activities, and isothermal microcalorimetry during 60 days. FDA and SA activities as well as overall soil microbial activity were significantly affected by Ni, SBX and Ni/SBX mixture. The inhibition rate (I) of the growth rate constant (k) being higher with the Ni/SBX mixture than with SBX alone during the experiment. The growth rate constant (k) was positively correlated (p < 0.05 or p < 0.01) with enzyme activities (FDA and SA) indicating that k represented a valuable proxy to evaluate the toxic effect of metals and flotation reagents on soil microorganisms. Thus, microcalorimetry was a useful method to characterize soil microbial communities.

Toxic metal(loid)s released from tailing residues of mining operations have become a global issue with regard to environmental impacts. Biochar derived from the agriculture waste is considered as a cost-effective and stable material, which could be applied for remediation of sites contaminated with toxic metal(loid)s. In the present study, tailings were amended for 90 days with increasing concentrations of Arundo donax L. stem-derived biochar (ASBC; at 0, 1, 3, and 5%). The 7-day wheat seed germination toxicity test was then used to assess the bioavailability of toxicants in aqueous leachates of the biochar-amended tailing samples. Concentrations of As, Cd, Cu, Pb, and Sb in leachates and the Community Bureau of Reference chemical fractions were determined using ICP-OES. The results indicated that tailing leachates were phytotoxic, an effect that was partially decreased due to increasing concentrations of ASBC, with maximum effects (∼47% of tailing phytotoxicity) occurring at 3% ASBC. Results of further fractionation analyses indicated that increasing concentrations of ASBC amendment decreased the mobile fractions of Cd, Cu, and Pb in tailing samples, but increased the mobilities of As and Sb. A novel approach using the relative toxicity index (= sum of toxicities of individual potentially toxic elements) indicated that the toxicity of the tailings decreased when As was not present, since As decreased the biochar-reduced toxicity. Our results suggest that the ability of using biochar to decrease toxicity in tailings (by sequestration of cationic metals such as Cd, Cu, and Pb) is limited by its inability to immobilize oxyanionic metalloids such as As and Sb.