Persistent organic pollutants in soil near the Changwengluozha glacier of the Central Tibetan Plateau, China: their sorption to clays and implication

Selected pesticidal POPs and metabolites in the soil of five Vietnamese cities: Sources, fate, and health risk implications

Large quantities of organochlorine pesticides (OCPs) have been used in tropical regions. The fate processes and risks of these legacy contaminants in the tropics are poorly understood. Herein, we investigated the occurrence of three classes of widely used OCPs and their metabolites in surface and core soil from five cities across Vietnam with a prevalent tropical monsoon climate and a long history of OCP application. We aimed to elucidate migration potentials, degradation conditions, and transformation pathways and assess current health risks of these contaminants. Generally, the concentrations of OCPs and metabolites in the soil core were slightly lower than those in surface soil except for hexachlorocyclohexane (HCH) isomers. 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane (p,p'-DDT), 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE), the sum of dicofol and 4,4'-dichlorobenzophenone (p,p'-DBP), and 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (p,p'-DDD) were the most abundant compounds in both surface and core soils. A uniform distribution of HCHs (the sum of α-, β-, γ-, and δ-HCH) at trace levels was found in almost all soils, serving as evidence of the lack of recent use of HCH pesticides. Higher concentrations of DDTs (the sum of DDT, DDD, and DDE) were observed in north-central Vietnamese soil, whereas appreciable concentrations of ENDs (the sum of α- and β-endosulfan and endosulfan sulfate) were only found in southern Vietnamese soils. Empirical diagnostic ratios indicated residuals of DDTs were mainly from technical DDT rather than dicofol, whereas aged HCHs could be explained by the mixture of lindane and technical HCH. Both historical applications and recent input explain DDTs and ENDs in Vietnamese soil. Total organic carbon performs well in preventing vertical migration of more hydrophobic DDTs and ENDs. The dominant transformation pathway of DDT in surface soil followed p,p'-DDE→2,2-bis(4-chlorophenyl)-1-chloroethylene or p,p'-DDMU→1,1-bis(4-chlorophenyl)ethylene or p,p'-DDNU→p,p'-DBP, whereas the amount of p,p'-DDMU converted from p,p'-DDD and p,p'-DDE is similar in soil core. Non-cancer risks of OCPs and metabolites in all soils and cancer risks of those chemicals in core soils were below the safety threshold, whereas a small proportion of surface soil exhibited potential cancer risk after considering the exposure pathway of vegetable intake. This study implied that organic matter in non-rainforest tropical deep soils still could hinder the leaching of hydrophobic organic contaminants as in subtropical and temperate soils. When lands with a history of OCP application are used for agricultural purposes, dietary-related risks need to be carefully assessed.

Pesticide pestilence: Global scenario and recent advances in detection and degradation methods

Increased anthropogenic activities are confronted as the main cause for rising environmental and health concerns globally, presenting an indisputable threat to both environment and human well-being. Modern-day industrialization has given rise to a cascade of concurrent environmental and health challenges. The global human population is growing at an alarming rate, posing tremendous pressure on future food security, and healthy and environmentally sustainable diets for all. To feed all, the global food production needs to increase by 50% by 2050, but this increase has to occur from the limited arable land, and under the present-day climate variabilities. Pesticides have become an integral component of contemporary agricultural system, safeguarding crops from pests and diseases and their use must be reduce to fulfill the SDG (Sustainable Development Goals) agenda . However, their indiscriminate use, lengthy half-lives, and high persistence in soil and aquatic ecosystems have impacted global sustainability, overshot the planetary boundaries and damaged the pure sources of life with severe and negative impacts on environmental and human health. Here in this review, we have provided an overview of the background of pesticide use and pollution status and action strategies of top pesticide-using nations. Additionally, we have summarized biosensor-based methodologies for the rapid detection of pesticide residue. Finally, omics-based approaches and their role in pesticide mitigation and sustainable development have been discussed qualitatively. The main aim of this review is to provide the scientific facts for pesticide management and application and to provide a clean, green, and sustainable environment for future generations.

Outdoor Atmospheric Micro-/Nanomineral-Mediated Organochlorine Pesticides in Sichuan Basin, China: Adsorption, Occurrence, and Risk Assessment

Atmospheric micro-/nanominerals play an important role in the adsorption, enrichment, and migration of organochlorine pesticides (OCPs). In the present study, the correlations between OCPs and minerals in outdoor atmospheric dustfall were investigated, and the correlations were used to speculate the source of p,p'-(dicofol+dichlorobenzophenone [DBP]), which is the sum of p,p'-dicofol and p,p'-DBP. Atmospheric dustfall samples were collected from 53 sites in the Chengdu-Deyang-Mianyang economic region in the Sichuan basin. In this region, 24 OCPs were analyzed by gas chromatography-tandem mass spectrometry. The average concentration of 24 OCPs was 51.2 ± 27.4 ng/g. The results showed that the concentration of Σ₂₄ OCPs in urban areas was higher than that in suburban areas (p < 0.05). Minerals in atmospheric dustfall were semiquantitatively analyzed by X-ray diffraction. The primary minerals were quartz, calcite, and gypsum. A Spearman correlation analysis of OCPs and minerals showed that low-volatility OCPs could be adsorbed by minerals in atmospheric dustfall. A density functional theory simulation verified that p,p'-(dicofol+DBP) in atmospheric dustfall was primarily derived from the p,p'-dicofol adsorbed by gypsum. Isomeric ratio results suggested that the samples had weathered lindane and chlordane profiles and confirmed that residents in the Sichuan basin used technical dichlorodiphenyltrichloroethane. Finally, the OCPs were evaluated to determine the potential risk of cancer in adults and children from OCP exposure. Exposure to OCPs via atmospheric dustfall was safe for adults. The cancer risk for children exposed to OCPs was slightly lower than the threshold value (10^-6 ) under a high dust ingestion rate, which poses a concern. Environ Toxicol Chem 2023;42:594-604. © 2022 SETAC.

Level and risk assessment of selected polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and organochlorine pesticides in walnut and soil

It is unknown how hydrophobic organic contaminants (HOCs) are distributed and how they affect the environment in high-fat nuts and their planted soil. The profile of HOCs in walnut/soil system was investigated in this study. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine pesticides (OCPs) were found in walnuts at concentrations of 0.67, 127, and 116 μg/kg, respectively. The target hazard quotients (THQ) of 17 PCBs, 16 PAHs, and 21 OCPs from walnut consumption by human were 0.06, 0.01, and 0.11, respectively. The highest concentrations of HOC in the soil were found in Nap and toxaphene, with concentrations of 2580 and 902 μg/kg, respectively. Bioaccumulation factors (BAF) and biota-sediment accumulation factors (BSAF) in walnuts were ranged from <0.01 to 7.04 and <0.01 to 3.83, respectively. Concentrations of most individual HOCs in soil samples were significantly correlated with soil organic matter (SOM) (p < 0.01) and minerals (p < 0.01), with maximum correlation coefficients of 0.70 (OM-PCB81) and -0.84 (P-BaP). According to this study, high-fat walnuts do not have a high bioaccumulation of HOCs from soil, and the risk of consumption is within the safe range.

A nationwide survey on the endosulfan residues in Chinese cotton field soil: Occurrence, trend, and ecological risk

The nationwide occurrence of endosulfan residues in cotton fields has not yet been investigated. Therefore, in this study, 202 surface soil samples from 27 cities were collected from cotton fields in 8 major cotton-planting provinces of China, covering more than 97% of the national cotton sown area. The results showed that endosulfan residues were detected in cotton fields throughout the country. The main type of residue found was endosulfan sulfate (ES-sulfate), followed by β-endosulfan and α-endosulfan, with average concentrations of 0.475, 0.129, and 0.048 μg/kg, respectively. Significant spatial variations in the endosulfan residues was noted, and the highest concentration of endosulfan residues was observed in the northwest inland cotton-growing area, followed by that in the Yellow River basin and Yangtze River basin cotton-growing areas. The endosulfan residues showed significant positive correlations with soil organic matter and soil clay contents. The α/β endosulfan ratio was determined to be in the range of 0.02-1.20, indicating that endosulfan residues originated from the endosulfan application performed in historical cotton cultivation efforts. Together with the literature data, the concentrations of α-endosulfan and β-endosulfan residues peaked in 2015 and 2017, respectively, and showed an overall decreasing trend from 2002 to 2021. The results of the ecological risk assessment suggested that Folsomia candida was most sensitive to endosulfan residues, with 20.8% of the sites presenting a high risk. However, in general, the soil ecological risk of cotton fields across the country was low. Our study demonstrated that China has achieved promising results in controlling the use and pollution of endosulfan, especially after 2014.

Soil-air partitioning of semivolatile organic compounds in the Lesser Himalaya region: Influence of soil organic matter, atmospheric transport processes and secondary emissions

After decades of imposed regulations about reducing the primary emissions of persistent organic pollutants (POPs), these pollutants are still present in the environment. Soils are important repositories of such persistent semivolatile organic contaminants (SVOCs), and it is assumed that SVOCs sequestered in these reservoirs are being re-mobilized due to anthropogenic influence. In this study, concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in soil and air, their fugacities, fluxes and the soil-air partition coefficient (K_SA) were determined for three different land cover types (glacial, remote/mountainous and urban) of the Lesser Himalayan Region (LHR). The concentrations of OCPs, PCBs and PBDEs in soils and air ranged between 0.01 and 2.8, 0.81-4.8, 0.089-0.75 ng g^-1; 0.2-106, 0.027-182, and 0.011-7.26 pg m^-3, respectively. The levels of SVOCs in the soil were correlated with soil organic matter (SOM) indicating that SOM is a substrate for the organic pollutants in soils. The Clausius-Clapeyron plots between ln P and inverse of temperature (1000/T) suggested that long range atmospheric transport was the major input source of PBDEs and higher chlorinated PCBs over the LHR. The uneven and wide distribution of local sources in LHR and up-slope enrichment of SVOCs explained the spatial variability and altitudinal patterns. The soils near mountain and urban lakes act as local sinks of SVOCs such as β-HCH, pp΄-DDT, CB-28, -118, -153, BDE-47, -99, and -154, with soil-air exchange fluxes tending more toward deposition. However, the soils near glacial lakes acted as local sources of more volatile congeners of α-HCH, γ-HCH, op'-DDT, pp'-DDE and lower to medium chlorinated PCBs such as CB-18, -28, -53, -42 and BDE-47, -99, with soil-air exchange tending more toward volatilization flux.

Chemical hazard in glacial melt? The glacial system as a secondary source of POPs (in the Northern Hemisphere). A systematic review

Toxicity of compounds belonging to persistent organic pollutants (POPs) is widely known, and their re-emission from glaciers has been conclusively demonstrated. However, the harmful effects associated with such secondary emissions have yet to be thoroughly understood, especially in the spatial and temporal context, as the existing literature has a clear sampling bias with the best recognition of sites in the European Alps. In this review, we elaborated on the hazards associated with the rapid melting of glaciers releasing organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs). To this end, we collated knowledge on: (1) the varying glacier melt rate across the Northern Hemisphere, (2) the content of POPs in the glacial system components, including the less represented areas, (3) the mechanisms of POPs transfer through the glacial system, including the importance of immediate emission from snow melt, (4) risk assessment associated with POPs re-emission. Based on the limited existing information, the health risk of drinking glacial water can be considered negligible, but consuming aquatic organisms from these waters may increase the risk of cancer. Remoteness from emission sources is a leading factor in the presence of such risk, yet the Arctic is likely to be more exposed to it in the future due to large-scale processes shifting atmospheric pollution and the continuous supply of snow. For future risk monitoring, we recommend to explore the synergistic toxic effects of multiple contaminants and fill the gaps in the spatial distribution of data.

Quantification of the sorption of organic pollutants to minerals via an improved mathematical model accounting for associations between minerals and soil organic matter

The retention of organic pollutant (OP) in soils is commonly attributed to interactions with soil organic matter (SOM), perhaps overlooking substantial involvement of soil minerals. In this study, 36 soil samples with far-ranging ratios of clay to organic carbon were used to examine contribution of minerals on soil sorption of pentachlorophenol (PCP) and phenanthrene (PHE). Sorption isotherms (n = 216) were fit individually using three typical sorption models, with the most fitted K_d values screened out for quantification of the net mineral contribution to total sorption via development of mathematical model accounting for associations between minerals and SOM. Two mineral-relevant parameters [adsorption distribution coefficient (K_min) and mineral contribution index (MCI)] were simultaneously defined. Previously reported soil sorption data of PCP, PHE and butachlor (13, 12 and 46, respectively) were also extracted and included to improve the credibility of mathematic model. The average MCI values were calculated as 0.421, 0.405 and 0.512 in PCP, PHE and butachlor treated soils, respectively, very close to or even over than the minerals dominant critical value (0.5). This suggested the significant, or even predominant, contribution of minerals - as compared to SOM. Significant dependence of MCI with four conventional parameters of soil property further offered the possibility to roughly evaluate mineral contributions based on estimated threshold values of soil property parameters (especially TOC). This study provides an accessible approach for predicting the contribution of minerals in soil OP retention, especially highlighting their predominant roles vs. SOM in regulating OP removal in most of subsurface soil or contaminated brownfields where organic carbon content of soil was very low, that was not like what previously believed.

Polycyclic aromatic hydrocarbons in sedimentary cores of Tibetan Plateau: Influence of global warming on cold trapping

Cold condensation is an important pathway for polycyclic aromatic hydrocarbons (PAHs) depositing at remote alpine lakes after long-range atmospheric transportation. However, in the context of global warming, the obvious temperature rise in the Tibetan Plateau (TP) might have an impact on the air deposition of PAHs by controlling the extent of cold condensation. To investigate the influence of rising temperatures on the atmospheric deposition of PAHs, two dated sedimentary cores from Pumoyum Co Lake (PC) and Selin Co Lake (SC) were collected, respectively and concentrations of 16 individual PAHs were measured. In both PC and SC, the total concentration of 16 PAHs presented relatively lower levels in four historical periods of "hot anomaly" including 1973-1975, 1988-1989, 1998-1999, and 2006-2007. This indicated that the hot temperatures might restrict the atmospheric deposition of PAHs. Besides, the results of the principal component analysis did discriminate those "hot anomalies". As the temperature kept increasing in TP, for low molecular weight PAHs and high molecular weight PAHs, the influence of rising temperatures on the cold condensation was different. Therefore, it was identified that the effect of global warming on the environmental fate of POPs cannot be neglected, especially in alpine regions like TP.

Agriculture Development, Pesticide Application and Its Impact on the Environment

Pesticides are indispensable in agricultural production. They have been used by farmers to control weeds and insects, and their remarkable increases in agricultural products have been reported. The increase in the world's population in the 20th century could not have been possible without a parallel increase in food production. About one-third of agricultural products are produced depending on the application of pesticides. Without the use of pesticides, there would be a 78% loss of fruit production, a 54% loss of vegetable production, and a 32% loss of cereal production. Therefore, pesticides play a critical role in reducing diseases and increasing crop yields worldwide. Thus, it is essential to discuss the agricultural development process; the historical perspective, types and specific uses of pesticides; and pesticide behavior, its contamination, and adverse effects on the natural environment. The review study indicates that agricultural development has a long history in many places around the world. The history of pesticide use can be divided into three periods of time. Pesticides are classified by different classification terms such as chemical classes, functional groups, modes of action, and toxicity. Pesticides are used to kill pests and control weeds using chemical ingredients; hence, they can also be toxic to other organisms, including birds, fish, beneficial insects, and non-target plants, as well as air, water, soil, and crops. Moreover, pesticide contamination moves away from the target plants, resulting in environmental pollution. Such chemical residues impact human health through environmental and food contamination. In addition, climate change-related factors also impact on pesticide application and result in increased pesticide usage and pesticide pollution. Therefore, this review will provide the scientific information necessary for pesticide application and management in the future.

Bioremediation of PAH-Contaminated Soils: Process Enhancement through Composting/Compost

Bioremediation of contaminated soils has gained increasing interest in recent years as a low-cost and environmentally friendly technology to clean soils polluted with anthropogenic contaminants. However, some organic pollutants in soil have a low biodegradability or are not bioavailable, which hampers the use of bioremediation for their removal. This is the case of polycyclic aromatic hydrocarbons (PAHs), which normally are stable and hydrophobic chemical structures. In this review, several approaches for the decontamination of PAH-polluted soil are presented and discussed in detail. The use of compost as biostimulation- and bioaugmentation-coupled technologies are described in detail, and some parameters, such as the stability of compost, deserve special attention to obtain better results. Composting as an ex situ technology, with the use of some specific products like surfactants, is also discussed. In summary, the use of compost and composting are promising technologies (in all the approaches presented) for the bioremediation of PAH-contaminated soils.

First evaluation of legacy persistent organic pollutant contamination status of stranded Yangtze finless porpoises along the Yangtze River Basin, China

Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis), inhabiting the Yangtze River, are an endangered species in China. They are threatened by various kinds of pollutants, among which persistent organic pollutants (POPs) are of special concern due to their toxicities, high persistency and bioaccumulation potential. To better understand the POP contamination status of Yangtze finless porpoises, an investigation of stranded porpoises along the Yangtze River and adjacent two major lakes in the Yangtze River basin was conducted; the concentrations of four groups of legacy POPs, i.e., hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyl (PCBs), were determined in the blubber samples. The mean concentrations of ΣHCHs (the sum of all congeners/isomers), ΣDDTs, ΣPBDEs and ΣPCBs, were 1670 ± 4210, 28,800 ± 52,300, 141 ± 174, and 1020 ± 1070 ng/g lipid weight, respectively; the high DDTs/PCBs ratio reflected a strong influence of agricultural pollution in the Yangtze River basin, and the high α/γ ratio of HCH isomers indicated the usage of lindane in the corresponding areas; the predominance of low-brominated congeners of PBDEs may be related to congruent patterns in the related environmental matrices. A hazard quotient risk assessment revealed that DDTs could pose a relatively high risk to Yangtze finless porpoises compared with the risks posed by the other POPs.

Influence of sediment parameters on the distribution and fate of PAHs in an estuarine tropical region located in the Brazilian semi-arid (Jaguaribe River, Ceará coast)

18 polycyclic aromatic hydrocarbons (PAHs) were evaluated in the Jaguaribe River to explore the influence of grain size, organic carbon, humic and fulvic acids and black carbon on their adsorption onto sediment. The ∑PAHs concentrations variated from 0.6 to 3752.0 ng g^-1 with highest concentrations in the estuarine zone. The PAHs predominant source along the river was from mixed sources, mainly related to biomass combustion, small oil spills related to recreational nautical activities and runoff from cities. Organic and inorganic parameters presented influence on PAHs distribution along the river, with humic acid as a determinant factor. These research findings are of importance to an assessment of the fate and transport of PAHs in estuarine systems.

The implications of water extractable organic matter (WEOM) on the sorption of typical parent, alkyl and N/O/S-containing polycyclic aromatic hydrocarbons (PAHs) by microplastics

Microplastics sorption of persistent organic pollutants (POPs) was the core processes that cause negative effects to biota, and their influencing factors and related mechanisms are poorly understood. In this study, we explored the impacts of water extractable organic matter (WEOM), an important source of endogenous dissolved organic matter in mangrove sediment, on the sorption coefficients of typical parent, alkyl and N/O/S-containing polycyclic aromatic hydrocarbons (PAHs) by microplastics. The presence of L-WEOM (D) impeded the PAHs sorption as the coefficients (K_f) decreased to 10.17 (μg/kg)/(μg/L)ⁿ and to 8.39 (μg/kg)/(μg/L)ⁿ for fluorene (Flu) and 1-methyl-fluorene (1-M-Flu), respectively. The K_f exhibited good linear relationships with the aliphaticity of L-WEOM (p < 0.05) rather than the aromatic carbon/alkyl carbon content (p > 0.05). Under the presences of L-WEOM (D), (S) and (K), the lone pair electrons of N/O/S-containing PAHs was the dominant factor contributing to the obvious difference of the K_f values from the other groups. Moreover, the largest impact of L-WEOM (D) on the Flu sorption was in the case of PVC microplastics, while almost no effect was in the case of PS microplastics. The findings of our work may be helpful in improving our understanding of the role of WEOM on the sorption of PAHs to microplastics in the field mangrove sediment.

Sorption kinetics, isotherms, and mechanism of aniline aerofloat to agricultural soils with various physicochemical properties

Aniline aerofloat (AAF), a high-toxic organic flotation reagent, is widely used in mineral processing industry. However, little information on its environmental fate is available. AAF sorption to four types of agricultural soils at low concentrations (1-10 mg/L) was investigated using batch experiments. AAF sorption kinetics involved both boundary layer diffusion and intraparticle diffusion, following pseudo-second-order kinetics with equilibrium time within 120 min. Both Langmuir and Freundlich models fitted well the AAF sorption with the former better. Sorption of AAF to soils was a spontaneous and favorable physical sorption that was controlled by ion bridge effect and hydrophobic interaction that was related to van der Waals force and π-π coordination based on FTIR analyses. AAF sorption was remarkably affected by soil constituents, positively correlating with the contents of organic matter and clay. The relatively higher logK_oc values (3.53-4.66) of AAF at environmental concentrations (1-5 mg/L) imply that soils are serving as a sink of AAF from beneficiation wastewater, posing great potential risks to environment and human health.

Sources and transformation pathways for dichlorodiphenyltrichloroethane (DDT) and metabolites in soils from Northwest Fujian, China

Dicofol (2,2,2-trichloro-1,1-bis-(p-chlorophenyl)ethanol) found in the environment is not only a miticide originated from commercial use, but also a metabolite of dichlorodiphenyltrichloroethane (DDT), which is often overlooked. To verify the sources and transformation pathways of DDT and related metabolites in soils, we measured p,p'-(dicofol + DBP) (sum of p,p'-dicofol and 4,4'-dichlorobenzophenone), DDT and six metabolites in soils from Northwest Fujian, China. The ratios of 1,1,1-trichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p'-DDT)/1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) and the mass balance demonstrated that p,p'-(dicofol + DBP) predominantly originated from p,p'-DDT transformation rather than from actual dicofol application. p,p'-(dicofol + DBP) accounted for 45.0% as the primary metabolites of DDT in this study, more than 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE) and 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD), which might lead to large overestimations of the fresh DDT input by using the traditional ratio of (∑₂DDD + ∑₂DDE)/∑₂DDT (with all o,p'- and p,p'- isomers included). In paddy fields where the conditions alternate between aerobic (dry period) and anaerobic (wet period), both p,p'-DDD and p,p'-DDE were likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU), which further transformed to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). Degradation of p,p'-DDMU to p,p'-DDNU mainly occurred in waterlogged paddy soils. However, p,p'-DDNU might not transform to other higher-order metabolites in aerobic surface soils. Overall, our study confirmed p,p'-(dicofol + DBP) as metabolites of p,p'-DDT, suggested DDE and DDD were parallel precursors of DDMU, and further verified the transformation pathways of DDT in surface soils.

The potential impact on the biodegradation of organic pollutants from composting technology for soil remediation

Large numbers of organic pollutants (OPs), such as polycyclic aromatic hydrocarbons, pesticides and petroleum, are discharged into soil, posing a huge threat to natural environment. Traditional chemical and physical remediation technologies are either incompetent or expensive, and may cause secondary pollution. The technology of soil composting or use of compost as soil amendment can utilize quantities of active microbes to degrade OPs with the help of available nutrients in the compost matrix. It is highly cost-effective for soil remediation. On the one hand, compost incorporated into contaminated soil is capable of increasing the organic matter content, which improves the soil environment and stimulates the metabolically activity of microbial community. On the other hand, the organic matter in composts would increase the adsorption of OPs and affect their bioavailability, leading to decreased fraction available for microorganism-mediated degradation. Some advanced instrumental analytical approaches developed in recent years may be adopted to expound this process. Therefore, the study on bioavailability of OPs in soil is extremely important for the application of composting technology. This work will discuss the changes of physical and chemical properties of contaminated soils and the bioavailability of OPs by the adsorption of composting matrix. The characteristics of OPs, types and compositions of compost amendments, soil/compost ratio and compost distribution influence the bioavailability of OPs. In addition, the impact of composting factors (composting temperature, co-substrates and exogenous microorganisms) on the removal and bioavailability of OPs is also studied.

Organochlorine pesticides in the sedimentary core of the southern Tibetan Plateau: The missing pieces induced by lateral remobilization

The sedimentary core in remote alpine lakes has been recognized as an ideal proxy to reconstruct the emission and air deposition histories of persistent organic pollutants (POPs). Nevertheless, POPs formerly stored in a catchment might also contribute to the variation in the lake sediment by lateral remobilization. In this study, to reveal the relative importance of lateral remobilization, we measured the vertical profiles and isomeric ratios of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs) and endosulfan in a dated sedimentary core collected from Lake Yamzho Yumco in the southern Tibetan Plateau. In addition to the flux peaks in the 1970s corresponding to the heavy atmospheric deposition of DDTs and HCHs, these pollutants' fluxes displayed rebounds in the flood periods, with characteristic low ratios of DDT/DDE (α-/β-HCH). This might indicate a massive remobilization of "weathered" pesticides from catchment soil to the lake because of strong hydro-dynamics. Moreover, the relative contribution of lateral remobilization to the lake sediment in the past decades was recognized through the correlation between DDT/DDE (α-/β-HCH) ratios and ∑DDT (∑HCH) fluxes. The results showed that the lateral remobilization contributed to 20-42% of the total fluxes. This study discriminated the air deposition from the contribution of lateral remobilization, which improves current understanding of the vertical POPs profiles in the sedimentary core.

The emerging source of polycyclic aromatic hydrocarbons from mining in the Tibetan Plateau: Distributions and contributions in background soils

The Tibetan Plateau (TP) serves as the background for persistent organic pollutants around the world. In addition to outside sources, local sources greatly contribute to the environment of the TP in recent decades. Mining activity could serve as an emerging source of polycyclic aromatic hydrocarbons (PAHs), although this issue has been neglected in the TP until now. To investigate the distributions and contributions of PAHs transported from mining activity, forty-one surface soil samples along six sampling directions were collected at a regular distance from the Jiama mining area (JMA) of the TP at altitudes between 3726 and 4863m. The total concentration of 16 PAHs was 52.34±22.58ng/g. The result of the source identification suggested that mining activity represented the primary source for heavy molecular weight (HMW) PAHs in soils, while light molecular weight (LMW) and middle molecular weight (MMW) PAHs were contributed by multiple sources. For HMW PAHs, the concentrations and proportions decreased logarithmically with transport distance from the JMA. Furthermore, the transport distance of HMW PAHs was found to be affected by the prevailing wind direction. In addition to transport from the source area, the distributions of LMW and MMW PAHs were also influenced by the altitude. In the impact area of Jiama mining activity, the soil mass inventory was estimated to be 6.4±0.8tons for HMW PAHs. In future decades, HMW PAHs emitted from Jiama mining activity are projected to exceed 5% of the annual local emission in the TP. Our study evidenced that Tibetan mining activity serves as an important emerging source of PAHs, which would be transported within the TP and threaten the fragile ecosystem of the TP.

Anthropogenic organochlorine compounds as potential tracers for regional water masses: A case study of estuarine plume, coastal eddy, wind-driven upwelling and long-range warm current

Water masses are the crucial factor driving the terrigenous anthropogenic organochlorine compounds (OCs) migration from the coast to open sea. Therefore, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were investigated in the Northern South China Sea (NSCS), where different types of water masses are generated by the East Asian summer monsoon: Pearl River estuary plume (PREP), Guangdong offshore eddy (GDEC), South China Sea warm current (SCSWC) and wind-driven upwelling current (WDUC). No discrepant distributions of OC concentrations were found in these water masses (p > 0.05). However, compositions and diagnostic ratios of HCHs, DDTs, trans- or cis-chlordane and PCBs could reflect the discrepancies in the input, transport and transformation of OCs caused by the hydrological characteristics of water masses, therefore, this allowing them to serve as potential tracers of regional water masses. In detail, α/γ-HCH and β-HCH percentages could indicate the weathered residue in the GDEC, long-range transport in the SCSWC, rapid photodegradation in the surface WDUC and biodegradation in the deep WDUC, respectively. The predominance of o, p'-DDT and p, p'-DDT could indicate fresh input in the PREP, GDEC and WDUC. DDT/DDTs of ratios <0.5 also reflected long-range transport in the SCSWC. Different DDD/DDE ratios indicated different oxygen environments of microbial degradation in the surface and deep water of the WDUC. Trans/cis-chlordane ratios could indicate the selective degradation of trans-chlordane in different water masses. Finally, a higher proportion of penta-PCB could reflect the strong paint additive sources carried by river erosion in the PREP.

Sources, atmospheric transport and deposition mechanism of organochlorine pesticides in soils of the Tibetan Plateau

Because of mountain cold-trapping, the soil in the Tibetan Plateau may be an important global sink of organochlorine pesticides (OCPs). However, there are limited data on OCPs in the soils of the Tibetan Plateau. In addition, the atmospheric transport and deposition mechanisms of OCPs also need to be further studied. In this study, the sampling area covered most regions of the Tibetan Plateau. The detection frequencies of ΣChlordane (sum of trans-chlordane, cis-chlordane and oxychlordane), HCB, ΣNonachlor (sum of trans- and cis-nonachlor), DDTs, ΣEndo (sum of endosulfan-I, endosulfan-II and endosulfate), aldrin, HCHs, ΣHeptachlor (sum of heptachlor and heptachlor epoxide), mirex and dieldrin were 100%, 98.3%, 96.6%, 94.8%, 89.7%, 87.9%, 62.1%, 55.2%, 32.8% and 6.9%, respectively. DDTs (with arithmetic mean values of 1050ngkg^-1 dw) and HCHs (393ngkg^-1) were the principal OCPs in cultivated soils, whereas ΣEndo (192ngkg^-1) and ΣChlordane (152ngkg^-1) were the principal OCPs in non-cultivated soils. Local use of DDTs, dicofol and HCHs may be an important source of OCP accumulation in the soil of the Tibetan Plateau. Aldrin and endosulfan are considered to be good indicators for studying atmospheric transport and deposition of OCPs from South Asia and Southeast Asia. Two zones with high OCP levels were found in the southeast and northwest of the Tibetan Plateau. The zones have dissimilar pollution sources of OCPs and are influenced by different factors that affect their precipitation scavenging efficiency. The amount of precipitation was the dominant factor in the southeast, whereas large differences in temperature and wind speed were the dominant factors in the northwest.

Composition and sources of polycyclic aromatic hydrocarbons in cryoconites of the Tibetan Plateau glaciers

Dark-colored cryoconite can absorb substantial solar radiation, reduce the surface albedo of glaciers, and thus greatly accelerate glacier melting. Organic matters in cryoconites such as polycyclic aromatic hydrocarbons (PAHs) are kind of the light absorbing compositions. In this study, 15 PAHs containing 3-7 rings were identified in 61 cryoconites samples collected from seven glaciers over the Tibetan Plateau (TP). The average concentration of total PAHs in cryoconites samples was in the range of 6.67-3906.66ngg^-1 dry weight. The highest average total PAH concentration was found in the southeastern TP, followed by the northern TP. The central TP contained the lowest amount of PAHs. Moreover, correlation analysis showed that total organic carbon (TOC) and grain size were only a minor factor for the accumulation of PAHs in cryoconites of the TP. Factor analysis and diagnostic ratios indicated that the PAHs were produced mainly from the incomplete combustion of coal, fossil fuels and biomasses. The exhaust gas of locomotives also contributed to the accumulation of PAHs in the glaciers. The PAHs in these seven glaciers showed low toxic equivalent quantity (TEQ), and thus had low biological risk. Nevertheless, the pollution of PAHs in the southeastern TP needs to be addressed.

Evidence for persistent organic pollutants released from melting glacier in the central Tibetan Plateau, China

Glacier alluvial deposits record persistent organic pollutants (POPs) not only derived from the atmospheric deposition but also from the release of glacial melting. The evidence for melting glacier in the Tibetan Plateau (TP) as a secondary source of pollutants is introduced through investigating the concentration of organochlorine pesticides (OCPs) in four deposited profiles collected at the edge of the Changwengluozha glacier. Two concentration peaks were observed for dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) in the past century. The first peak was observed in the 1970s, corresponding with the heavy usage of HCHs and DDTs in the surrounding countries and regions. The second one was in 2000 when the production and usage of DDTs and HCHs were strictly limited, which possibly indicated a significant release from melting glacier. This result was further supported by the enantiomeric fraction values for α-HCH and o,p'-DDT. On the other hand, the dramatic increase of polycyclic aromatic hydrocarbons (PAHs) from atmospheric deposition, which was associated with the socioeconomic development in Tibet, shaded the release of PAHs from melting glacier. This study reveals not only the air deposition history of legacy POPs but also a substantial release of OCPs from glacier to the adjacent environment. Our research supports the hypothesis that the melting glacier in the TP represents a secondary source of OCPs, which is consistent with the findings in the Alps glaciers.

A review of current knowledge and future prospects regarding persistent organic pollutants over the Tibetan Plateau

Since the turn of the century, our understanding of the quantities, transport pathways, and fate of persistent organic pollutants (POPs) over the Tibetan Plateau (TP), the largest and highest plateau on Earth, has greatly enhanced. We begin in this article by reviewing the available literature on the levels of POPs over the TP. In general, the levels of most POPs are similar or lower than values reported for other background regions. However, dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) levels in air and soil far exceed those measured in other mountainous areas. The East Asian monsoon, Indian Monsoon and westerly winds are responsible for the long-range atmospheric transport (LRAT) and arrival of POPs over the TP. Surface soil and vegetation act as "final sinks" for DDTs and other high molecular weight POPs. Linked to the continuous use of POPs in surrounding counties, LRAT and "cold trapping" by the TP can happen following emission-transport-deposition events, leading to the enrichment of POPs in the TP environment. Bioaccumulation of DDTs and high chlorinated PCBs have been found in Tibetan terrestrial and aquatic food chains, and newly emerging compounds such as polyfluoroalkyl substances and hexabromocyclododecanes have been widely detected in wild fish species. The corresponding ecological risks should be of great concern. Climate change, such as increased temperatures and changing coverage of snow and glaciers, has the potential to affect the behavior and distribution of POPs. Therefore, long-term monitoring data are required. Ineffective regulation regarding POPs has been reported for countries in South Asia, emissions patterns, the outflow of POPs, and their seasonal and inter-annual variability should therefore be clarified. Estimating the loading of POPs, as well as how they move, within the TP, especially under the impact of glacial melt and global warming, should be a priority.

An overview on the organic pollution around the Qinghai-Tibet plateau: The thought-provoking situation

The Qinghai-Tibet Plateau plays an important role in the ecological safety and human health of the surroundings due to its unique geographical position and function. Therefore, it is necessary to study the pollution status and potential risk in this area. This study summarizes the distribution of different organic pollutants in biota and environmental media of the Qinghai-Tibet Plateau. Moreover, it also pays attention to the potential health risks of these organic pollutants. Organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were the most frequently detected in different matrices. In general, the carcinogenic risks of organic pollutants were ranked in the very-low to moderate range for both children and adults. The carcinogenic risks of organic pollutants in fish, food, and water for children were 1-2 times higher than those for adults, while risks of organic pollutants in soil/sediment and in air for children were generally 10.6-16.5 and 2.6-2.8 times higher than those for adults, respectively. The maximal hazard quotient for non-carcinogenic risk was 0.95 (potential risk for children posed by organic pollutants in yak milk of Ruoergai), almost reaching an unacceptable level. Therefore, the potential health risks could not be neglected, especially for children who were more likely to be affected by the pollutants.

One century of air deposition of hydrocarbons recorded in travertine in North Tibetan Plateau, China: Sources and evolution

The characteristic distribution patterns of hydrocarbons have been used for fingerprinting to identify their sources. The historical air depositions of hydrocarbons recorded in natural media help to understand the evolution of the air environment. Travertine is a natural acceptor of air deposition that settles on the ground layer by layer. To reconstruct the historical air environment of hydrocarbons in the North Tibetan Plateau (NTP), a unique background region, twenty-seven travertine samples were collected systematically from a travertine column according to its precipitated year. For each sample, the precipitated year was dated while n-alkanes and polycyclic aromatic hydrocarbons (PAHs) were determined. Based on source identification, the air environment of hydrocarbons in the past century was studied for the region of NTP. Before World War II, the anthropogenic sources of hydrocarbons showed little influence on the air environment. During World War II and China's War of Liberation, hydrocarbons increased significantly, mainly from the use of fossil fuels. Between 1954 and 1963, hydrocarbons in the air decreased significantly because the sources of petroleum combustion decreased. From the mid-1960s through the end of the 1990s, air hydrocarbons, which mainly originated from biomass burning, increased gradually because agriculture and animal husbandry were developing steadily in Tibet and China. From the late 1990s, hydrocarbons in the atmosphere increased rapidly due to the rapid increase of tourism activities, which might increase hydrocarbon emissions from traffic. The reconstruction of the historical air hydrocarbons in NTP clearly reflects the evolution of the region and global development.

Sorption of dodecyltrimethylammonium chloride (DTAC) to agricultural soils

Quaternary ammonium compounds (QACs) used as cationic surfactants are intensively released into environment to be pollutants receiving more and more concerns. Sorption of dodecyltrimethylammonium chloride (DTAC), one of commonly used alkyl QACs, to five types of agricultural soils at low concentrations (1-50mg/L) was investigated using batch experiments. DTAC sorption followed pseudo-second-order kinetics and reached reaction equilibrium within 120min. Both Freundlich model and Langmuir model fitted well with DTAC isotherm data with the latter better. DTAC sorption was spontaneous and favorable, presenting a physical sorption dominated by ion exchanges. Sorption distribution coefficient and sorption affinity demonstrated that soil clay contents acted as a predominant phase of DTAC sorption. DTAC could display a higher mobility and potential accumulation in crops in the soils with lower clay contents and lower pH values. Sorption of DTAC was heavily affected by ions in solution with anion promotion and cation inhibition.

Identification of sources of polycyclic aromatic hydrocarbons based on concentrations in soils from two sides of the Himalayas between China and Nepal

To understand distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in the Himalayas, 77 soil samples were collected from the northern side of the Himalayas, China (NSHC), and the southern side of the Himalayas, Nepal (SSHN), based on altitude, land use and possible trans-boundary transport of PAHs driven by wind from Nepal to the Tibetan Plateau, China. Soils from the SSHN had mean PAH concentration greater than those from the NSHC. Greater concentrations of PAHs in soils were mainly distributed near main roads and agricultural and urban areas. PAHs with 2-3 rings were the most abundant PAHs in the soils from the Himalayas. Concentrations of volatile PAHs were significantly and positively correlated with altitude. Simulations of trajectories of air masses indicated that distributions of soil PAH concentrations were associated with the cyclic patterns of the monsoon. PAH emissions from traffic and combustion of biomass or coal greatly contributed to concentrations of PAHs in soils from the Himalayas.

Diurnal Variations of Air-Soil Exchange of Semivolatile Organic Compounds (PAHs, PCBs, OCPs, and PBDEs) in a Central European Receptor Area

Concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs) in air and soil, their fugacities, and the experimental soil-air partitioning coefficient (KSA) were determined at two background sites in the Gt. Hungarian Plain in August 2013. The concentrations of the semivolatile organic compounds (SOCs) in the soil were not correlated with the organic carbon content but with two indirect parameters of mineralization and aromaticity, suggesting that soil organic matter quality is an important parameter affecting the sorption of SOCs onto soils. Predictions based on the assumption that absorption is the dominant process were in good agreement with the measurements for PAHs, OCPs, and the low chlorinated PCBs. In general, soils were found to be a source of PAHs, high chlorinated PCBs, the majority of OCPs and PBDEs, and a sink for the low chlorinated PCBs and γ-hexachlorocyclohexane. Diurnal variations in the direction of the soil-air exchange were found for two compounds (i.e., pentachlorobenzene and p,p'-dichlorodiphenyldichloroethane), with volatilization during the day and deposition in the night. The concentrations of most SOCs in the near-ground atmosphere were dominated by revolatilization from the soil.

Polycyclic aromatic hydrocarbons in soils of the central Tibetan Plateau, China: Distribution, sources, transport and contribution in global cycling

Forty-four soil samples were collected across the central Tibetan Plateau (CTP) at altitudes between 3711 m and 5352 m, and their polycyclic aromatic hydrocarbons (PAHs) contents were measured to be from 0.43 to 26.66 ng/g. The main sources of PAHs were identified for each of four sub-areas, and their concentrations in soils were determined to be mainly influenced by local sources. Along a 600 km sampling trajectory from Lhasa, which served as the biggest local source, the concentrations of PAHs decreased logarithmically with increasing distances from the source. Meanwhile, the fractional proportions of PAHs were observed to change logarithmically according to the transport distances. Conclusively, PAHs from local sources were transported within the CTP and dominated PAHs concentrations in the soils, but few of them were transported outside the CTP. In global cycling, the soils in the CTP mainly serve as background and a "sink" for PAHs.

Polybrominated diphenyl ethers in surface soils near the Changwengluozha Glacier of Central Tibetan Plateau, China

Forty-two congeners of polybrominated diphenyl ethers (PBDEs) were detected for each of 27 surface-soil samples collected at an area near the Changwengluozha Glacier in the Central Tibetan Plateau (CTP), a remote background area at altitude from 5080 to 5217 m. The total concentrations of BDEs in soils ranged from 15.3 to 248.0 ng/kg, which were found to be positively correlated with the clay contents in the soil. In addition to adsorption, the clay was found to serve as a catalyst for the debromination of PBDEs in soils. Three pieces of evidence confirmed that the clay was significantly correlated with the debrominating transformation from the higher brominated congeners to the less brominated congeners. The transforming rate was found to be increased 3.5% with a 10% increase in clays. Debromination is an important way for highly brominated congeners to transform into lighter brominated congeners that are more toxic. This study first provided the direct field evidences for clays contributing to the debromination of PBDEs, and elucidated the importance of it in PBDEs' environmental fate.

Sorption/desorption of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane(4,4'-DDT) on a sandy loam soil

1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane(4,4'-DDT) is a pesticide well-known for its negative health and environmental effects. Despite being banned by a majority of world countries more than 30 years ago, its persistence in the environment is a continuing problem even today. The objective of the study was the investigation of sorption/desorption behavior of 4,4'-DDT in sandy loam soil. The impact of contaminant concentration and age was observed with three different experiments. The sorption percentages at the end of the short time step (8 h) were 50 and 92 %, for initial concentrations 2.26 and 5.28 mg/L, respectively. When freshly spiked soil was subjected to a conventional sorption study, 82 to 99.6 % of the initial aqueous DDT concentrations were sorbed within 24 h. When modeled with a Freundlich isotherm, the log K f was found to be 3.62. After six consecutive 24 h desorption steps, 33 to 96.6 % still remained in the soil. This was more pronounced for soils that had been aged for 60 days. After seven consecutive 24 h desorption steps of aged soil, the percent remaining sorbed to the soil were 44, 64, and 77 %, for 25, 250, and 500 mg/kg, respectively. All results show that 4,4-DDT has a tendency of sorbing to the soil rapidly and showing resistance to desorption. When comparing desorption values, aged soils were seen to desorb less than non-aged soils. This result was attributed to stronger binding to soil with increased contact time.

Polychlorinated biphenyls in surface soils of the Central Tibetan Plateau: altitudinal and chiral signatures

The soils in the Central Tibetan Plateau (CTP), which is a unique background region, play an important role in the fate of the global cycling of polychlorinated biphenyls (PCBs). Forty-four soil samples from across the CTP were collected at altitudes between 3711 m and 5352 m, and the concentrations of 122 PCB congeners were measured from 66.98 to 150.81 ng/kg. The concentration of PCBs was positively correlated with the sampling altitude and clay content. Furthermore, enantiomeric fractions (EFs) of CB-95, CB-136 and CB-149 in soils of CTP were first determined. A (+)-enantiomer excess was identified for CB-136 and CB-149 in all of the samples investigated. Additionally, enantiomer-specific excess was found for CB-95. The dominance of enantiomer-specific excess decreased with increased the sampling altitude and congener concentration. It is likely that the addition of enantiomeric mixtures of PCBs from the atmosphere changed the EFs in the soils according to the altitude.

Chiral signature of α-HCH and o,p'-DDT in the soil and grass of the Central Tibetan Plateau, China

Enantiomeric fraction (EF) of organochlorine pesticides (OCPs) has been used as a signature for tracing the source and following pathways. The chiral analysis was performed for α-HCH and o,p'-DDT in paired soil and grass samples from the Central Tibetan Plateau (CTP), a unique background region. In the case of α-HCH, excess of (-) α-HCH was predominant in 83.3% of soil samples, and 80% of grass samples showed excess of (+) enantiomer. For o,p'-DDT, 90.9% of grass samples showed excess of (-) o,p'-DDT while 50% of soil samples showed excess of the (-) enantiomer. A correlation between EFs of soil and grass was not observed for either compound. The EFs of both compounds were correlated with soil concentration and with change of sampling altitude, within EFs being lower than racemic. However, these trends were not found in grass. Our study provides a database of EFs and signatures for OCPs in the CTP, one background region of the world.

Correlations between PAH bioavailability, degrading bacteria, and soil characteristics during PAH biodegradation in five diffusely contaminated dissimilar soils

The natural biodegradation of seven polycyclic aromatic hydrocarbons (PAHs) by native microorganisms was studied in five soils from Normandy (France) from diffusely polluted areas, which can also pose a problem in terms of surfaces and amounts of contaminated soils. Bioavailability tests using cyclodextrin-based extractions were performed. The natural degradation of low molecular weight (LMW) PAHs was not strongly correlated to their bioavailability due to their sorption to geosorbents. Conversely, the very low degradation of high molecular weight (HMW) PAHs was partly correlated to their poor availability, due to their sorption on complexes of organic matter and kaolinites or smectites. A principal component analysis allowed us to distinguish between the respective degradation behaviors of LMW and HMW PAHs. LMW PAHs were degraded in less than 2-3 months and were strongly influenced by the relative percentage of phenanthrene-degrading bacteria over total bacteria in soils. HMW PAHs were not significantly degraded, not only because they were less bioavailable but also because of a lack of degrading microorganisms. Benzo[a]pyrene stood apart since it was partly degraded in acidic soils, probably because of a catabolic cooperation between bacteria and fungi.