Environmental contamination and human exposure of polychlorinated biphenyls (PCBs) in China: A review

Polychlorinated biphenyls (PCBs), together with 11 other organic compounds, were initially listed as persistent organic pollutants (POPs) by the Stockholm Convention because of their potential threat to ecosystems and humans. In China, many monitoring studies have been undertaken to reveal the level of PCBs in environment since 2005 due to the introduced stricter environmental regulations. However, there are still significant gaps in understanding the overall spatial and temporal distributions of PCBs in China. This review systematically discusses the occurrence and distribution of PCBs in environmental matrices, organisms, and humans in China. Results showed that PCB contamination in northern and southern China was not significantly different, but the PCB levels in East China were commonly higher than those in West China, which might have been due to the widespread consumption of PCBs and intensive human activities in East China. Serious PCB contamination was found in e-waste disassembling areas (e.g., Taizhou of Zhejiang Province and Qingyuan and Guiyu of Guangdong Province). Higher PCB concentrations were also chronicled in megalopolises and industrial clusters. The unintentionally produced PCBs (UP-PCBs) formed during industrial thermal processes may play an increasingly significant role in PCB pollution in China. Low PCB levels were recorded in rural and underdeveloped districts, particularly in remote and high-altitude localities such as the Tibetan Plateau and the South China Sea. However, these data are limited. Human exposure to PCBs is closely related to the characteristics of environmental pollution. This review also discusses existing issues and future research prospects on PCBs in China. For instance, the accumulation characteristics and migration regularities of PCBs in food webs should be further studied. More investigations should be undertaken to assess the quantitative relationship between external and internal exposure to PCBs. For example, bioaccessibility and bioavailability studies should be supplemented to evaluate human health risks more accurately.

Sedimentary evolution of PAHs, POPs and ECs: Historical sedimentary deposition and evolution of persistent and emerging organic pollutants in sediments in a typical karstic river basin

Knowledge on the occurrence and distributions of organic compounds, especially PAHs, POPs and ECs, in karstic river basins is limited. This study aims to determine the depositional history and sources of PAHs, PCBs, OCPs, antibiotics, EDCs and phenolic compounds and the ecological risk they have in the Panyang River Basin, an area with a typical karstic landscape and a high-longevity population. Sediment core analysis was adopted, correlation and principal component analyses were conducted to analyze pollution sources, and lead isotope technology was implemented for dating analysis. The sediment core covered 108 years. PCBs were detected with concentrations ranging from 3.80 to 16.18 μg/kg in the core with two concentration peaks in 1950 and 2005 that were related to anthropogenic effects. Eight of the 20 targeted phenolic compounds were detected, with concentrations ranging from 0.42 to 1.10 mg/kg. All PAHs were detected in the cores, with concentrations from 12.91 to 37.80 μg/kg. They were mainly related to natural diagenetic processes and domestic and agricultural sources. The concentrations of different OCP compounds ranged from undetected to 213.43 μg/kg and were mainly related to agricultural activities and long-range transportation. These key findings can assist environmental planning and management in this river basin.

Occurrence and sources of PCBs, PCNs, and HCB in the atmosphere at a regional background site in east China: Implications for combustion sources

Multiple types of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), and hexachlorobenzene (HCB), can be unintentionally released from combustion or thermal industrial processes, which are speculated to be the main sources of these contaminants, as they were banned on production and use since several decades ago. In this study, concentrations and sources of 40 PCBs, 39 PCNs, and HCB were analyzed in air samples collected during the period 2012-2015 at a background site in east China. ΣPCBs, ΣPCNs, and HCB were in the range of 9-341 pg/m³, 6-143 pg/m³, and 14-522 pg/m³, respectively. Seasonal characteristics with high levels in winter and low levels in summer were observed for PCNs and HCB. PCBs also exhibited slightly higher levels in winter. Source apportionment was conducted, using polycyclic aromatic hydrocarbons (PAHs) as combustion sources indicator, combined with principal component analysis (PCA) and positive matrix factorization (PMF) model. The results indicated that the legacy of past produced and used commercial PCBs was the dominant contributor (∼56%) to the selected PCBs in the atmosphere in east China. PCNs were mainly emitted from combustion sources (∼64%), whereas HCB almost entirely originated from combustion process (>90%).

Accumulation and fate processes of organochlorine pesticides (OCPs) in soil profiles in Mt. Shergyla, Tibetan Plateau: A comparison on different forest types

Previous work documented that forest plays an important role in the deposition of persistent organic pollutants (POPs) in the southeast Tibetan Plateau (TP) due to the "forest filter effect". However, forest types in the southeast TP are entirely different and the influence on POPs fate and forest filter effect by different forests remains unclear. This study focused on the distribution and transfer of organochlorine pesticides (OCPs) in soil of different forest types (quercus, birch, fir, and spruce dominated forests) in Mt. Shergyla, southeast TP under similar environmental and meteorological conditions. Total levels of ∑HCHs, ∑DDTs and HCB in soils ranged from < LOD to 2.25 ng/g dry weight (dw), < LOD-10.2 ng/g dw, and < LOD-0.95 ng/g dw, respectively. Concentrations of OCPs in humus layers were significantly higher than those in mineral layers in the four forest types. Relatively higher ∑DDTs concentrations were found in soil profile of broadleaved birch forest, while higher concentrations of ∑HCHs and HCB were found in soil profile of coniferous fir forest, and the same trend was observed in fresh leaf samples. Air-to-ground fluxes and mobility of OCPs in the four forest types were also evaluated. Relatively higher fluxes were found in fir forests than in other forest types, suggesting that fir forest could be more effective to transfer OCPs from the air into soil in the southeast TP. The findings in this study would be helpful for improving model simulation of POPs fate in different forest ecosystem.

Seasonal variations and sources of atmospheric polycyclic aromatic hydrocarbons and organochlorine compounds in a high-altitude city: Evidence from four-year observations

Lijiang is a high-altitude city located on the eastern fringe of the Tibetan Plateau, with complex seasonal atmospheric circulations (i.e. westerly wind, Indian Monsoon, and East Asia Monsoon). Very few previous studies have focused on seasonal variations and sources of organic pollutants in Lijiang. In this study, a four-year air campaign from June 2009 to July 2013 was conducted to investigate the temporal trends and the sources of polycyclic aromatic hydrocarbons (PAHs) and organochlorine compounds [including organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs)]. The atmospheric PAH concentrations in winter are 2-3 times of those in summer, probably because of the combined result of enhanced local emission and long-range atmospheric transport (LRAT) during winter. Traffic pollution was the primary local source of PAHs, while biomass burning is the dominant LRAT source. OCPs and PCBs also mainly underwent LRAT to reach Lijiang. The peak concentrations of most of OCPs occurred in pre-monsoon season and winter, which were carried by air masses from Myanmar and India through westerly winds. As compared with other sites of the Tibetan Plateau, without the direct barrier of the Himalaya, Lijiang is easily contaminated by the incursion of polluted air masses.

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.

Observations of atmospheric pollutants at Lhasa during 2014-2015: Pollution status and the influence of meteorological factors

Atmospheric pollutants including SO₂, NO₂, CO, O₃ and inhalable particulate matter (PM_2.5 and PM₁₀) were monitored continuously from March 2014 to February 2015 to investigate characteristics of air pollution at Lhasa, Tibetan Plateau. Species exhibited similar seasonal variations except O₃, with the peaks in winter but low valleys in summer. The maximum O₃ concentration was observed in spring, followed by summer, autumn, and winter. The positive correlation between O₃ and PM₁₀ in spring indicated similar sources of them, and was assumed to be turbulent transport. Temperature was the dominant meteorological factor for most species in spring. High temperature accelerates O₃ photochemistry, and favors air disturbance which is conductive to dust resuspension in spring. Relative humidity (RH) and atmospheric pressure were the main meteorological factors in summer. RH showed negative correlations with species, while atmospheric pressure posed opposite situation. Wind speed (WS) was the dominant meteorological factor in autumn, the negative correlations between WS and species indicated diffusion by wind. Most species showed non-significant correlations with meteorological factors in winter, indicating the dependence of pollution on source emission rather than restriction by meteorology. Pollution weather character indicated that emissions were from biomass burning and dust suspension, and meteorological factors also played an important role. Air stream injection from the stratosphere was observed during O₃ pollution period. Air parcels from Southwest Asia were observed during air pollution period in winter. An enhancement in air pollutants such as O₃ would be expected in the future, more attention should be given to countermeasures for prevention of air pollution in the future.

Occurrence and air-soil exchange of organochlorine pesticides and polychlorinated biphenyls at a CAWNET background site in central China: Implications for influencing factors and fate

Ambient air and soil samples were collected between March 2012 and March 2013 at Jinsha, a regional background site in central China, to measure the concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). The average concentrations of total OCPs and total PCBs were 191 ± 107 and 39.4 ± 27.1 pg/m³ in air (gaseous and particulate phase) and 0.585 ± 0.437 and 0.083 ± 0.039 ng/g in soil, respectively. The higher concentrations of p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) and p,p'-DDT/p,p'-DDE ratios in the soil indicated recent p,p'-DDT input to the soil. A strong positive temperature dependence and average fugacity fraction value > 0.5 were observed for p,p'-DDT, suggesting that volatilization of residual DDT in the soil was the main influencing factor on atmospheric p,p'-DDT. Highly average fugacity fractions (>0.7) of trans-chlordane (TC) and cis-chlordane (CC) and high TC/CC ratios both in the soil and atmosphere suggested fresh inputs. Higher gaseous concentrations of hexachlorobenzene (HCB) were observed in winter and negative temperature dependence was directly attributed to the surrounding ongoing source (e.g. fuel consuming activities), especially in winter. Overall, most targeted OCPs and PCBs were influenced by long-range transport, and fugacity fraction values indicated highly volatile compounds (e.g. α-hexachlorocyclohexane (α-HCH) and lower chlorinated PCBs) were volatilized and low volatility compounds (e.g. p,p'-DDE and higher chlorinated PCBs) were deposited at the air-soil interface. Knowing the source and sink of OCPs and PCBs can help to control their pollution in this area and provide a reference for other studies.

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.

Organochlorine pesticide distribution in an organic production system for cow's milk in Chiapas, Mexico

The objective of this study was to evaluate the presence of organochlorine pesticides in samples of forage, soil, water, and milk in four units of an organic production system for cow´s milk (samples of forage, milk, soil, and water) in Tecpatan, Chiapas, Mexico. The organochlorine pesticides were extracted from forage, soil and water based on the USEPA (2005) guideline and from milk based on the IDF 1991 guideline. The pesticides were identified and quantified by gas chromatography with electron capture detector (CG-ECD). In general, the highest average concentration of total pesticides was found in the samples of milk and forage (311 ± 328 and 116.5 ±77 ng g(-1) respectively). Although, the production systems analyzed are organic, organochlorine pesticides were detected in all environmental samples (forage, soil, water, and organic milk). Although no values surpassed the defined limits of Mexican and International regulation it is advisable that a monitoring program of contaminants in these production systems is continued.

Current status of persistent organic pesticides residues in air, water, and soil, and their possible effect on neighboring countries: a comprehensive review of India

Though the use of pesticides has offered significant economic benefits by enhancing the production and yield of food and fibers and the prevention of vector-borne diseases, evidence suggests that their use has adversely affected the health of human populations and the environment. Pesticides have been widely distributed and their traces can be detected in all areas of the environment (air, water and soil). Despite the ban of DDT and HCH in India, they are still in use, both in domestic and agricultural settings. In this comprehensive review, we discuss the production and consumption of persistent organic pesticides, their maximum residual limit (MRL) and the presence of persistent organic pesticides in multicomponent environmental samples (air, water and soil) from India. In order to highlight the global distribution of persistent organic pesticides and their impact on neighboring countries and regions, the role of persistent organic pesticides in Indian region is reviewed. Based on a review of research papers and modeling simulations, it can be concluded that India is one of the major contributors of global persistent organic pesticide distribution. This review also considers the health impacts of persistent organic pesticides, the regulatory measures for persistent organic pesticides, and the status of India's commitment towards the elimination of persistent organic pesticides.

DDT and HCH, two discontinued organochlorine insecticides in the Great Lakes region: isomer trends and sources

The uses of the insecticides 1,1'-(2,2,2-trichloroethylidene)bis[4-chlorobenzene] (p,p'-DDT) and γ-hexachlorocyclohexane (γ-HCH) have been discontinued for several years, but they are still consistently detected in air samples collected on the shores of the Great Lakes. Although the agricultural uses of DDT have been restricted in the United States since 1972, DDT continued to be used to manufacture the miticide, dicofol, up until 2011. The use of the technical HCH mixture in North America was restricted in the 1970s, when it was replaced by one of its purified conformers, γ-HCH, also known as lindane. In this study, we have focused on isomer-specific data to gain insights on the temporal trends and possible sources of these compounds. In particular, we calculated ratios of the concentrations of p,p'-DDE+p,p'-DDD versus the sum of the concentrations of the three p,p' isomers. These ratios are about the same at all five of our sampling sites and are about the same as observed globally. We also calculated the ratio of the concentrations of o,p'-DDT versus the sum of concentrations of o,p'-DDT+p,p'-DDT. This ratio has increased significantly at all five sites over the last 15-20 years. We suggest that dicofol, which contained about 11% o,p'-DDT, may now be a significant, additional source of DDT to the Great Lakes. The average ratio of the concentration of γ-HCH (lindane) versus the sum of the concentrations of γ-HCH+α-HCH did not vary significantly with time, but it did show an urban signature, suggesting that cities may be more important sources of these compounds than previously suspected.