Global trade-driven transfer of atmospheric polycyclic aromatic hydrocarbon emissions and associated human inhalation exposure risk.

Polycyclic aromatic hydrocarbons (PAHs) are of significant public concern because of their toxicity and long-range transport potential. Extensive studies have been conducted to explore the source-receptor relationships of PAHs via atmospheric transport. However, the transfer of trade-driven regional and global PAHs is poorly understood. This study estimated the virtual PAHs emission transfer embodied in global trade from 2004 to 2014 and simulated the impact of international trade on global contamination and associated human inhalation exposure risk of PAHs. Results show that trade-driven PAHs flowed primarily from developed to less-developed regions, particularly in those regions with intensive heavy industries and transportation. As the result, international trade resulted in an increasing risk of lung cancer induced by exposure to PAHs (27.8% in China, 14.7% in India, and 11.3% in Southeast Asia). In contrast, we found decreasing risks of PAHs-induced lung cancer in Western Europe (63.2%) and the United States (45.9%) in 2004. Our findings indicate that final demand and emission intensity are the key driving factors contributing to rising and falling consumption-based PAHs emissions and related health risk respectively. The results could provide a useful reference for global collaboration in the reduction of PAHs pollution and related health risks.

Contamination, ecological-health risks, and sources of potentially toxic elements in road-dust sediments and soils of the largest urban riverfront scenic park in China.

Identifying the contamination and sources of potentially toxic elements (PTEs) in road-dust sediment (RDS) and the surrounding greenspace soil of urban environments and understanding their ecological-health risks are important for pollution management and public health. The contamination characteristics, ecological and probabilistic health risks, and source apportionment of eight PTEs (Cd, Pb, Cr, Cu, Ni, As, Zn, and Hg) in the Yellow River Custom Tourist Line of Lanzhou, which is the largest open urban riverfront scenic park in China, were investigated. The results showed that all the RDS PTE mean concentrations exceeded their soil background values, whereas for the surrounding greenspace soils, the concentrations of the PTEs, except for Cr and Ni, were also higher than their local background levels. Moreover, the RDS-soil system was mainly contaminated by Cd, Zn, Pb, Cu, and Hg to varying degrees, and the integrated ecological risks of PTEs in the RDS and soil were high and considerable at most sites, respectively. The probabilistic health risk assessment results demonstrated that the non-carcinogenic hazard risk for humans was negligible, but the total carcinogenic risks should be considered. Source apportionment using a positive matrix factorization model combined with multivariate statistical analyses revealed that Cr, Ni, and As in the RDS-soil system were from natural and industrial sources, Cd, Pb, Zn, Cu came from vehicle emissions and pesticide and fertilizer applications, and Hg was from natural and industrial sources and utilization of pesticides with fertilizers. This work provides scientific evidence for urban planning and human health protection in urban environments.

[Pollution Characteristics and Risk Assessment of Heavy Metals in Surface Dusts and Surrounding Green Land Soils from Yellow River Custom Tourist Line in Lanzhou].

In order to investigate the contamination levels of dust and its surrounding green land soil heavy metal pollution and potential ecological and health risks in the scenic areas of urban waterfront parks, the gardens, squares, and theme parks of the Yellow River Custom Tourist Line in Lanzhou were selected as the research area, using 27 dust samples and 26 soil samples from its surrounding green lands. The contamination characteristics and potential ecological risks of eight heavy metals (Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb) were evaluated using the geo-accumulation index (Igeo), single-factor pollution index (Pi), Nemerow integrated pollution index (PN), and improved potential ecological risk index (RI). The human health risk assessment was also evaluated using the exposure risk model. The results showed that the average concentrations of the other heavy metals in the surface dusts were higher than the background values of Gansu Province and Lanzhou City, except that the As mean concentrations in the surface dusts and the surrounding green land soils were slightly lower than the Gansu Province background values. For its surrounding green land soils, the mean concentrations of the other heavy metals (Cu, Zn, Cd, Hg, and Pb) exceeded the soil background values of Gansu Province and Lanzhou City, whereas the Cr and Ni mean concentrations were lower than their corresponding soil background values of Gansu Province and Lanzhou City. The geo-accumulation and single-factor pollution indices demonstrated that a slight to moderate pollution of Cr, Cu, Zn, Cd, Hg, and Pb occurred in surface dusts, and Cu, Zn, Cd, Hg, and Pb appeared in varying degrees of contamination levels in its surrounding green land soils. The Nemerow integrated pollution index analysis manifested that the overall contamination status of the study areas was between slightly and heavily polluted. The potential ecological risk index suggested that Cd and Hg were recognized as significant pollutant elements and that the RI of the other heavy metals were all below 40, presenting slight ecological risk. The health risk assessment indicated that ingestion was the dominant exposure pathway for heavy metals from the surface dusts and the surrounding green land soils, and no carcinogenic and noncarcinogenic risks posed threats to adults and children.

Assessing the contribution of global wildfire biomass burning to BaP contamination in the Arctic.

Polycyclic aromatic hydrocarbons (PAHs) have become cause for growing concern in the Arctic ecosystems, partly due to their stable levels despite global emission reduction. Wildfire is considered one of the primary sources that influence PAH levels and trends in the Arctic, but quantitative investigations of this influence are still lacking. This study estimates the global emissions of benzo[a]pyrene (BaP), a congener of PAHs with high carcinogenicity, from forest and grassland fires from 2001 to 2020 and simulates the contributions of wildfire-induced BaP emissions from different source regions to BaP contamination in the Arctic. We find that global wildfires contributed 29.3% to annual averaging BaP concentrations in the Arctic from 2001 to 2020. Additionally, we show that wildfires contributed significantly to BaP concentrations in the Arctic after 2011, enhancing it from 10.1% in 2011 to 83.9% in 2020. Our results reveal that wildfires accounted for 94.2% and 50.8% of BaP levels in the Asian Arctic during boreal summer and autumn, respectively, and 74.2% and 14.5% in the North American Arctic for the same seasons. The source-tagging approach identified that local wildfire biomass emissions were the largest source of BaP in the Arctic, accounting for 65.7% of its concentration, followed by those of Northern Asia (17.8%) and Northern North America (13.7%). Our findings anticipate wildfires to play a larger role in Arctic PAH contaminations alongside continually decreasing anthropogenic emissions and climate warming in the future.

Effects of African BaP emission from wildfire biomass burning on regional and global environment and human health.

The vegetation burning caused by wildfires can release significant quantities of aerosols and toxic chemicals into the atmosphere and result in health risk. Among these emitted pollutants, Benzo(a)pyrene (BaP), the most toxic congener of 16 parent PAHs (polycyclic aromatic hydrocarbons), has received widespread concerns because of its carcinogenicity to human health. Efforts have been made to investigate the environmental and health consequences of wildfire-induced BaP emissions in Africa. Still, uncertainties remain due to knowledge and data gaps in wildfire incidences and biomass burning emissions. Based on a newly-developed BaP emission inventory, the present study assesses quantitatively the BaP environment cycling in Africa and its effects on other continents from 2001 to 2014. The new inventory reveals the increasing contribution of BaP emission from African wildfires to the global total primarily from anthropogenic sources, accounting for 48% since the 2000 s. We identify significantly higher BaP emissions and concentrations across sub-Saharan Africa, where the annual averaged BaP concentrations were as high as 5-8 ng/m3. The modeled BaP concentrations were implemented to estimate the lifetime cancer risk (LCR) from the inhalation exposure to BaP concentrations. The results reveal that the LCR values in many African countries exceeded the acceptable risk level at 1 × 10-6, some of which suffer from very high exposure risk with the LCR>1 × 10-4. We show that the African BaP emission from wildfires contributed, to some extent, BaP contamination to Europe as well as other regions, depending on source proximity and atmospheric pathways under favorable atmospheric circulation patterns.

[Sources and Health Risks of Atmospheric Polychlorinated Biphenyls in an Urban/Industrial Areas, Northwest China].

A passive air sampler was used to monitor the concentration and contamination profile of 18 polychlorinated biphenyls (PCBs) in the atmosphere over the urban and industrial area of Gaolan, a city in northwest China, during the non-heating and heating seasons of 2018, and the sources, pollutant transport, and the health risks of PCB exposure were analyzed and assessed using principle component analysis, trajectory modeling, and inhalation exposure modeling. The atmospheric concentration in the study area ranged from 110.2 to 429.9 pg·m-3, and the highest average concentration was found at the industrial estate. Tetra-PCBs and penta-PCBs were the dominant homologue groups, and the percentage of tetra-PCBs increased in the heating season. Combustion and industrial thermal processes, PCB-containing electrical equipment, and the combined source of volatilization from paint, combustion, and industrial thermal processes were considered to be the main sources, and the source of combustion and industrial thermal processes contributed the largest proportion of PCBs at 40.8%. Largely, the emission of UP-PCBs would significantly influence PCB pollution in the study area. Trajectory analysis results illustrated that PCBs emitted from sources in the study area would be transmitted to Lanzhou City atmospherically; local pollution would be the main source of PCBs contamination in the study area during the non-heating season, while the atmospheric input of PCBs transmitted from the northwest region would be another source during the heating season. Health risk analysis showed that the non-cancer risk of PCBs exposure was low in all age groups; however, lifetime cancer risks exceeded 10-6. PCBs emitted from combustion and industrial thermal processes sources would have a strong impact on resident exposure to PCBs, and adverse health effects would be caused due to long-term inhalation exposure of the inhabitants to PCBs contamination in the study area.

[Atmospheric Pollution Characteristics and Inhalation Exposure Risk of Nitrated Polycyclic Aromatic Hydrocarbons in PM2.5 at the Ningdong Energy and Chemical Industry Base, Northwest China].

Atmospheric PM2.5 samples were collected by using the active sampling method to investigate the pollution characteristics of nitrated polycyclic aromatic hydrocarbons (NPAHs) at the Ningdong Energy and Chemical Industry Base, Northwest China. Furthermore, the primary sources and the contributions of secondary formation sources as well as the inhalation exposure risks were identified. The main results were as follows. The concentration levels of ∑12NPAHs in PM2.5 ranged from 2.06 ng·m-3 to 37.14 ng·m-3 at the Ningdong Energy and Chemical Industry Base. The average concentrations of ∑12NPAHs were (25.57±5.76) ng·m-3 in winter and (6.22±1.74) ng·m-3 in summer for the Baofeng sampling site associated with the energy industry. The average concentrations of ∑12NPAHs were (7.13±1.44) ng·m-3 in winter and (2.58±0.39) ng·m-3 in summer for the Yinglite sampling site associated with chemical and electricity industries. The levels of ∑12NPAHs in PM2.5 were higher in winter than those in summer because of the increased heating in winter. Atmospheric pollution levels of NPAHs at the Baofeng sampling site were generally higher than those at the Yinglite sampling because of the higher primary NPAHs emissions from coal mining and coke production in Baofeng compared with those from the chemical industry in Yinglite. The calculated nocturnal/diurnal ratios revealed that the concentrations of ∑12NPAHs in PM2.5 during the summer season were higher in the daytime than those in the nighttime, but the opposite trend occurred in winter, thus indicating that secondary formation processes made more contributions to NPAHs during summer in the daytime. The congener profiles of NPAHs were mainly composed of primary emission markers such as 2-nitrofluorene (2N-FLO) and 6-nitrochrysene (6N-CHR), which were the predominant ones in winter and summer for both the Baofeng and Yinglite sampling sites. Total proportions of 2N-FLO and 6N-CHR were 46% in winter and 73% in summer for Baofeng and 59% in winter and 55% in summer for Yinglite, respectively. Meanwhile, 3N-PHE, which is a marker compound of secondary formation processes, accounted for a higher percentage in summer especially at Yinglite. This finding revealed that the chemical production at Yinglite was associated with higher precursor emissions than that of Baofeng, and thus, more NPAHs were derived from secondary formation processes. Moreover, ∑12NPAHs/∑16PAHs ratios were calculated to identify the potential sources of NPAHs across the city. The results indicated that higher environmental temperatures in summer promoted the degradation of PAHs and secondary formation of NPAHs, and thus, secondary formation contributed more to NPAHs in summer than in winter. Furthermore, lung cancer risks induced by inhalation exposures to ∑5NPAHs were assessed based on the BaP equivalent toxicity factor. The results showed that the lung cancer risk values of ∑5NPAHs were (3.06×10-5±1.36×10-5) in winter and (1.79×10-5±0.80×10-5) in summer for the Baofeng sampling site, while the risk values were (2.85×10-5±1.20×10-5) in winter and (1.86×10-5±0.83×10-5) in summer for the Yinglite sampling site. Notably, the lung cancer risk values in our study for both sampling sites were higher than the standard limit value (1.00×10-5) of the California Environmental Protection Agency, which indicates that the local population at the Ningdong Energy and Chemical Industry Base has been subjected to potentially elevated lung cancer risks due to inhalation exposures to PM2.5-bound NPAHs.

[Pollution Characteristics and Occupational Exposure Risk of Heavy Metals in Indoor and Outdoor Ambient Particles at a Scaled Electronic Waste Dismantling Plant, Northwest China].

Atmospheric particle samples (PM1.0、PM2.5、PM10) were collected from three sampling sites (indoor and outdoor workplaces of a formal e-waste dismantling plant, and upwind area) in an arid area of Northwest China. The contents of six heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed using ICP-OES. Based on this data, the concentration levels, size distribution characteristics, and occupational exposure risks of heavy metals at the indoor and outdoor dismantling workplaces were studied. Particle analysis showed that Zn (4890 ng·m-3 indoors, 1245 ng·m-3 outdoors)、Pb (indoors 1201 ng·m-3, outdoors 240 ng·m-3), and Cu (indoors 1200 ng·m-3, outdoors 110 ng·m-3) showed higher pollution levels indoors and outdoors at the dismantling workplace. Moreover, the indoor concentration was much higher than that outdoors, indicating that the dismantling activity was the main cause of the high levels of heavy metal contamination. The indoor and outdoor air pollution characteristics were closely related to the types of electronic waste dismantled. Occupational exposure risk assessments showed that the total non-carcinogenic hazard quotient (HQ) of the indoor and outdoor dismantling workshops was 1.62×10-3, and 3.60×10-4, respectively, and the carcinogenic risk values were 2.69×10-7 and 2.59×10-9. Cd caused the greatest carcinogenic and non-carcinogenic risks at both indoor and outdoor dismantling workplaces, but it was still far below the limits (1.0) and acceptable ranges (1×10-6) stipulated by U.S. EPA, indicating that the health risks caused by heavy metals were minor or negligible. Heavy metals in the ambient particulate matter released from an adequately equipped and formally managed e-waste dismantling plant would not lead to any public health risk. The sedimentation characteristics of particulate heavy metals in different organs of the human respiratory system exhibited that the smaller the particle size was, the greater the proportion of deposition in the depths of the respiratory system was. Enterprises should make scientific and effective decisions on the respiratory health risks caused by such fine particles to the health of professional workers.

Estimating the spatial distribution of environmental suitability for female lung cancer mortality in China based on a novel statistical method.

Lung cancer as one of the major causes of cancer mortality has been demonstrated to be closely related to the ambient atmospheric environment, but little has been done in the synthetic evaluation of the linkage between cancer mortality and combined impact of ambient air pollution and meteorological conditions. The present study determined the environmental suitability for female lung cancer mortality associated with air contaminants and meteorological variables. A novel fuzzy matter-element method was applied to identify the spatial distribution and regions for the environmental suitability for the female lung cancer mortality across China in 2013. The membership functions between the cancer mortality and 6 environmental factors, including PM2.5, NO2, SO2, PM10, the annual mean wind speed, and mean temperature, were generated and the weights of each of the environmental factors were established by the maximum entropy (MaxEnt) model. We categorized the environmental suitability combined with GIS spatial analysis into three zones, including low-suitable, medium-suitable, and high-suitable region where the cancer mortality ranging from low to high rate was identified. These three zones were quantified by the MaxEnt model taking different air pollutants and meteorological variables into consideration. We identified that NO2 was a most significant factor among the 6 environmental factors with the weight of 24.88%, followed by the annual mean wind speed, SO2, and PM2.5. The high-suitable area, mainly in the North China Plain which is a most heavily contaminated region by air pollution in China, covers 1.6195 million square kilometers, accounting for 17.85% of the total area investigated in this study. Identification of the impact of various environmental factors on cancer mortality in the different suitable area provides a scientific basis for the environmental management, risk assessment, and lung cancer control.

Forecasting PM2.5 induced male lung cancer morbidity in China using satellite retrieved PM2.5 and spatial analysis.

The present study predicts a spatial distribution of lung cancer morbidity in Chinese males due to exposure to PM2.5 concentration from 2010 to 2015. A spatial autocorrelation method was used to evaluate the spatial relationship between the lung cancer morbidities from 2006 to 2009 and satellite-derived PM2.5 atmospheric levels. A comprehensive grey correlation degree analysis was carried out to assess the simultaneous and lag associations between the lung cancer morbidity and PM2.5 concentration. These relationships were subsequently applied to predict male lung cancer morbidity in a specific year. Annual mean PM2.5 levels in this specific year and previous 8years were used as 9 independent variables to establish four statistical models. These models include ridge regression (RR), partial least squares regression (PLSR), support vector regression (SVR), and the combined forecasting model (CFM) to predict the male lung cancer morbidity in China from 2010 to 2015. The model error evaluations suggested that the partial least squares regression model performed the best in the male lung cancer morbidity forecast. We calculated the male lung cancer morbidity by the optimal method among the established statistical forecasting models at 1948 sites in China. The gridded morbidity distribution from 2010 to 2015 across the country was obtained by Kriging interpolation method. Results showed that the male lung cancer morbidity increased significantly from western to eastern China, except for the far north region. This spatial pattern is in line with the spatial distribution of PM2.5 concentration, manifesting a significant relationship between PM2.5 concentration level and lung cancer morbidity in Chinese males.

Sources and potential health risk of gas phase PAHs in Hexi Corridor, Northwest China.

Gas phase polycyclic aromatic hydrocarbons (PAHs) in Hexi Corridor, Northwest China were determined during heating and non-heating seasons, respectively, using passive air samplers. Polyurethane foam (PUF) disks were chosen as the sampling medium. Fifteen PAHs out of the 16 PAHs classified by the United States Environmental Protection Agency (U.S. EPA) were detected in this field sampling investigation. The atmospheric levels of sampled PAHs were higher at urban sites than that at rural sites among 14 sampling sites and increased during heating season. The highest concentration (11.34 ng m(-3)) was observed in Lanzhou during the heating season, the capital and largest industrial city of Gansu Province. PAH contamination in air was dominated by three aromatic ring congeners. Possible sources of PAHs were apportioned using PAH species ratios and the principle component analysis (PCA) combined with a multiple linear regression (MLR) method. Fossil fuel consumption was identified to be the predominant source of PAHs over Hexi Corridor, accounting for 43 % of the concentration of total (15) PAHs. Backward and forward trajectory and cluster analysis were also carried out to identify potential origins of PAHs monitored at several urban and rural sites. Lung cancer risk of local residents to gas phase PAHs via inhalation exposure throughout the province was found to be around a critical value of the lung cancer risk level at 10(-6) recommended by the U.S. EPA risk assessment guideline.

[Ecological risk assessment of organophosphorus pesticides in aquatic ecosystems of Pearl River Estuary].

The risk quotient method and a probabilistic risk assessment method were applied for assessing aquatic ecological risk of nine organophosphorus pesticides, including thimet, dichlorovos, disulfoton, dimethoate, dimethyl parathion, chlorpyrifos, ethoprophos, sumithion and malathion on eight aquatic organisms in the Pearl River Estuary. Results using the risk quotient method revealed that the risk level of opossum shrimp was the highest among eight aquatic organisms of the Pearl River Estuary. The risk of water flea and midge was in medium level, followed by the rest six aquatic organisms, including diatom, oyster, carp, catfish and eel, which were in the low risk by the examined organophosphorus pesticides. It was found that thimet made the largest contribution to total aquatic ecological risk among nine organophosphorus pesticides to every organism. The results from probabilistic risk assessment showed that the total ecological risk in high water period was higher than that in low water period determined by the HC5 under the 95% confidence level. The largest contribution of thimet to total aquatic ecological risk subject to the HC5 in 50% confidence level was regarded as the toxic reference value. The probabilistic risk of a single contaminant showed that thimet and disulfoton were harmful to exceeded 10% organisms in the estuarine. The probabilistic risk of nine pesticides mixture in high water period was also higher than that in low water period, and both risks were greater than 5% which exceeded safety threshold for 95% organisms in the Pearl River Estuary.

[Residual levels in air, soil and soil-air exchange of organochlorine pesticides in Hami region of Xinjiang and its potential ecological risk].

The concentrations of HCHs and DDTs in soil and air of urban/rural/forestry centre locations in the Hami region of Xinjiang were monitored for a year by passive atmospheric sampling in order to study the residual levels and air-soil exchange and evaluate ecological risk. The study results showed that the annual average concentrations of HCHs and DDTs in the air of Hami were 107.1 pg x m(-3) and 43.9 pg x m(-3), respectively, and the concentrations of HCHs and DDTs in summer and autumn were generally higher than those in winter and spring. It was deduced that the HCHs and DDTs tended to evaporate into the air because of the higher temperatures in summer and autumn. For OCPs in the air of study area, HCHs were dominanted the main pollution compared with DDTs. Meanwhile, alpha-HCH contributed the largest portion among all HCHs isomers, and p,p'-DDE dominated the residual levels of DDTs. Moreover, the values of alpha-HCH/gamma-HCH were in the range of 3 to 7, which indicated that the use of technical HCHs or the long distance atmosphere transport of HCHs may play a significant role for HCHs in the air of Hami region. Furthermore, ratios of (DDD + DDE)/DDTs were in the range of 0.4-0.9, 71.4% of which were higher than 0.5, indicating that DDTs in the air were mainly from historical usage and no new DDTs sources emerged in Hami recently. The concentrations of HCHs and DDTs in soil were between 0.344-6.954 ng x g(-1) and 0.104-26.397 ng x g(-1), respectively, which did not exceed the National Soil Quality Standard Level I. In addition, DDTs predominated in soil OCPs, in which beta-HCH accounting for a huge percentage in HCHs isomers, while o,p'-DDT predominated in pollution caused by DDTs isomers. From study results, it was also suggested that the important cause of DDTs residues in soil of Hami area could be the recent inputs of new sources since the value of (DDD + DDE)/DDTs were lower than 0.5. The sources of HCHs and DDTs in soil and atmosphere were not consistent, which was mainly caused by the different characteristics of soil and atmosphere and the complex geographical environment and climatic conditions in Hami region. The study on air-soil exchange showed that the escaping tendency of the various isomers of HCHs and p, p'-DDE was mainly from the soil to the air, on the contrary, the escaping tendency of o,p'-DDE,o,p'-DDD,p,p'-DDD,o,p'-DDT,p,p'-DDT was mainly from the air to the soil in Hami, which indicated that the soil was the sink of most of DDTs, and the air was the source of most of DDTs; while the air was the sink of HCHs and p,p'-DDE, and the soil was the source of HCHs and p,p'-DDE. There were potential risks of DDTs to birds and soil organisms in urban soil and forestry centre soil of Hami region, while the ecological risk of HCHs was light in Hami surface soil.

[Seasonal variation and spatial distribution of typical organochlorine pesticides in the atmosphere of Hexi Corridor and Lanzhou, northwest China].

Air samples were seasonally collected in Hexi Corridor and Lanzhou, Gansu province, using polyurethane foam (PUF) based passive air samplers for a year and determined hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs). Atmospheric concentrations of sigma HCHs (alpha-HCH +beta-HCH +gamma-HCH +delta-HCH) and sigma DDTs (p,p'-DDT + o,p'-DDT + p,p'-DDE + p,p'-DDD) were 86.22 pg x m(-3) and 34.06 pg x m(-3) in Hexi Corridor and Lanzhou with background concentrations of 54.41 pg x m(-3) and 21.56 pg x m(-3), respectively, which were lower than previously reported values elsewhere. In general, the seasonal pollution characteristics of sigma HCHs and sigma DDTs exhibited higher levels with the average concentrations of 127.4 pg x m(-3) and 47.06 pg x m(-3) in autumn, respectively. Furthermore, relatively higher residual concentrations of HCHs and DDTs were found in Jiuquan, Anxi and Zhangye, relating to their more arable lands and more intensively historical usage. Source apportionment indicated HCHs were mainly originated from historical technical-HCHs residues and recent Lindane usage. Recently introduced technical-DDTs was highly responsible for DDTs contamination, whereas the higher concentrations of o,p'-DDT observed in Jiuquan and Anxi may be attributed to dicofol usage. In addition, human exposure to HCHs and DDTs in Hexi Corridor and Lanzhou via inhalation could be relatively low.