Does an analysis of polychlorinated biphenyl (PCB) distribution in mountain soils across China reveal a latitudinal fractionation paradox?

Occurrence and fate of current-use pesticides in Chinese forest soils

Pesticides play a crucial role in securing global food production to meet increasing demands. However, because of their pervasive use, they are now ubiquitous environmental pollutants that have adverse effects on both ecosystems and human health. In this study, the environmental occurrence and fate of 16 current-use pesticides (CUPs) were investigated in 93 forest soil samples obtained from 11 distinct mountains in China. The concentrations of the target pesticides ranged from 0.36 to 55 ng/g dry weight. Cypermethrin, dicofol, chlorpyrifos, chlorothalonil, and trifluralin were the most frequently detected CUPs. The CUP concentrations were generally higher in the O-horizon than in the A-horizon. Chlorpyrifos, chlorothalonil, and dicofol were detected in most deep layers in soil profiles from three mountains selected to represent distinct climate zones. No clear altitudinal trend in organic carbon-normalized concentrations of CUPs was observed in the O- or A-horizons within individual mountains. A negative correlation was noted between the CUP concentrations and the altitudes across all sampling sites. This indicated that proximity to emission sources was a key factor affecting the spatial distribution of CUPs in mountain forest soil on a national scale. The ecological risk assessment showed that dicofol and cypermethrin pose potential risks to earthworms. This study emphasizes the importance of source control when setting management strategies for CUPs.

Persistent organic pollutants in global surface soils: Distributions and fractionations

The distribution and fractionation of persistent organic pollutants (POPs) in different matrices refer to how these pollutants are dispersed and separated within various environmental compartments. This is a significant study area as it helps us understand the transport efficiencies and long-range transport potentials of POPs to enter remote areas, particularly polar regions. This study provides a comprehensive review of the progress in understanding the distribution and fractionation of POPs. We focus on the contributions of four intermedia processes (dry and wet depositions for gaseous and particulate POPs) and determine their transfer between air and soil. These processes are controlled by their partitioning between gaseous and particulate phases in the atmosphere. The distribution patterns and fractionations can be categorized into primary and secondary types. Equations are developed to quantificationally study the primary and secondary distributions and fractionations of POPs. The analysis results suggest that the transfer of low molecular weight (LMW) POPs from air to soil is mainly through gas diffusion and particle deposition, whereas high molecular weight (HMW) POPs are mainly via particle deposition. HMW-POPs tend to be trapped near the source, whereas LMW-POPs are more prone to undergo long-range atmospheric transport. This crucial distinction elucidates the primary reason behind their temperature-independent primary fractionation. However, the secondary distribution and fractionation can only be observed along a temperature gradient, such as latitudinal or altitudinal transects. An animation is produced by a one-dimensional transport model to simulate conceptively the transport of CB-28 and CB-180, revealing the similarities and differences between the primary and secondary distributions and fractionations. We suggest that the decreasing temperature trend along latitudes is not the major reason for POPs to be fractionated into the polar ecosystems, but drives the longer-term accumulation of POPs in cold climates or polar cold trapping.

Spatial redistribution and enantiomeric signatures of hexachlorocyclohexanes in Chinese forest soils: Implications to environmental behavior and influencing factors

Hexachlorocyclohexanes (HCHs) are a group of highly persistent pesticides. The concentrations of HCHs and the enantiomeric fractions of α-HCH in the O- and A-horizons from 30 mountains across China were analyzed in this study. The concentrations of total HCHs ranged from 0.061 to 46.9 ng/g (mean 2.12 ng/g) and 0.046 to 16.1 ng/g (mean 0.792 ng/g) in the O- and A-horizons, respectively. The HCH residues were mainly derived from the historical applications of technical HCH and lindane. Higher concentrations of HCHs were typically found in northern China, and no significant correlations were found between historical technical HCH usage and HCH isomer concentrations in either the O- or A-horizons (p > 0.05). Conversely, the concentrations of HCH isomers were significantly correlated with the environmental parameters (temperature and precipitation), thus indicating a typical secondary distribution pattern. Some HCH isomers tended to be transported northward under the long-term effect of monsoon. Chiral α-HCH was non-racemic in soils and showed preferential degradation of (-) α-HCH in both the O- and A-horizons. The transformation from γ-HCH to α-HCH might alter the enantiomeric signatures of α-HCH in soils. Moreover, the deviation from racemic of α-HCH was positively correlated with the C/N ratio in the A-horizon (p < 0.01), thus suggesting that the C/N ratio could alter the microbial activity and significantly affect the enantioselective degradation extent of α-HCH in soils.

Distribution, sources, and ecological risk assessment of polychlorinated biphenyls (PCBs) in the estuary of Dagu River, China

Four different types of 0-30 cm soil/sediment samples were collected from aquaculture land, farmland, industrial land and river bottom sediment in the estuary area of Dagu River, and the pollution status and sources of 7 PCB congeners were analyzed. The results showed that the mean values of Σ7PCBs in soil/sediments of different land use types were 5.01 ng g-1 dw for industrial land, 3.6 ng g-1 dw for estuarine sediments, 2.09 ng g-1 dw for farmland soil and 1.78 ng g-1 dw for farming land. All samples were at low pollution levels and pose little ecological risks. PCBs in the samples are mainly comprised of highly chlorinated biphenyls, and their content decreases gradually with increasing sampling depth. Based on the principal component analysis, it is concluded that the main source of PCBs in the study area is shipping activities, in addition to atmospheric transport and sedimentation sources.

Chlorinated organic pollutants in global flooded soil and sediments: Pollution status and potential risk

Chlorinated organic pollutants (COPs) were widely detected in anaerobic environments while there is limited understanding of their pollution status and potential environmental risks. Here, we applied meta-analysis to identify the occurrence status, pollution sources, and environmental risk of COPs from 246 peer-published literature, including 25 kinds of COPs from 977 sites. The results showed that the median concentrations of COPs were at the ng g^-1 level. By the combination of principal component analysis (PCA) and positive matrix factorization (PMF), we established 7 pollution sources for COPs. Environmental risk assessment found 73.3% of selected sites were at a security level but the rest were not, especially for the wetlands. The environmental risk of COPs was usually underestimated by the existing evaluation methods, such as without the consideration of the non-extractable residues (NER) and the multi-process coupling effect. Especially, the synergetic coupling associations between dechlorination and methanogenesis might increase the risk of methane emission that has barely been previously considered in previous risk assessment approaches. Our results expanded the knowledge for the pollution control and remediation of COPs in anaerobic environments.

Role of low-latitude forests in modulating forest filter effect on a continental scale: Long-term simulation on PCB-153 in Chinese forests

Forests are important compartments influencing the environmental fate of persistent organic pollutants (POPs). To illustrate the effect of forests on the regional cycle of POPs, a level IV fugacity fate and transport model coupled with a detailed dynamic-forest module was applied to simulate the long-term variations of PCB-153 in China, where forest coverage accounts for approximately one fifth of land area. In the scenarios with forests, atmospheric outflow from China was 69% of that in the scenario without forests due to the enhanced storage in soil, degradation, and leaching. Previous studies regarded high-latitude areas, such as the polar region and boreal forests, as environments capable of reducing mobility of PCB-153, and they act as sinks of POPs. This modeling result suggests that tropical and subtropical forests may also play a similar role despite high temperatures favoring volatilization. Unlike boreal forest, the low-latitude forests may reduce the overall lifetime of PCB-153 in China due to enhanced degradation in warmer and moist soils of the tropical and subtropical area. Given that approximately half of the global forests are located in tropical and subtropical regions, they can be important environments influencing the global geochemical cycle and distribution of POPs, hence deserving more scientific attention by modeling and empirical studies.

Levels and enantiomeric signatures of organochlorine pesticides in Chinese forest soils: Implications for sources and environmental behavior

We investigated the levels and distributions of organochlorine pesticides (OCPs) in 159 background soil samples collected from 30 forested mountain sites across China. The sum of DDT was the most abundant OCP, with the concentrations of 0.197-207 ng/g and 0.033-122 ng/g in the O-horizon and A-horizon, respectively. High concentrations of OCPs usually occur near agricultural regions or high consumption areas. The spatial distribution was mainly influenced by the emission sources and soil total organic contents (TOC). The chiral compounds were generally nonracemic in the soils and showed preferential degradation of (-) o,p'- dichlorodiphenyltrichloroethane, (+) trans-chlordane, and (-) cis-chlordane in both the O- and A-horizons. The enantiomeric fraction (EF) distributions of chiral OCPs displayed no differences across the forest sites in the O-horizon or the A-horizon. Comparing the deviation of EFs from racemic (DEVrac = absolute value of 0.500 - EF) with environmental parameters, we found that DEVrac of cis-chlordane demonstrated a strong positive correlation with TOC (p < 0.05) and the C/N ratio (p < 0.01). This relationship suggests that these factors could affect the microbial activity and significantly impact the extent of enantioselective degradation of chiral compounds in the soils. Fresh and historical applications of DDT and historical chlordane and endosulfan uses may be prominent sources of OCP accumulation in Chinese forest soils.

Concentrations and risks of polychlorinated biphenyls (PCBs) in transformer oils and the environment of a power plant in the Niger Delta, Nigeria

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Soils and water resources around the power plant are contaminated with PCBs.

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The hepta- and octa-PCB homologues were dominant in the samples.

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Exposure to PCBs in soils from the power plant could cause human health risk.

The concentrations of Ʃ14 PCBs were determined, with the aid of gas chromatography-mass spectrometry (GC–MS), in transformer/turbine oils, soils, groundwater, and drainage water collected within a power plant in the Niger Delta of Nigeria. The Ʃ14 PCB concentrations in the transformer oils, drainage water, groundwater and soils ranged from 484 to 48506 mg kg⁻¹, 0.99 to 2.95 mg L⁻¹, 0.16 to 0.56 mg L⁻¹ and from 8.4 to 510 mg kg⁻¹ respectively. The congener distribution patterns in these samples indicate the dominance of highly chlorinated homologues (hepta- and octa-PCBs). The Σ14 PCB concentrations in the transformer oils were above the provisional definition of low persistent organic pollutant (POP) content for PCBs of 50 mg kg⁻¹ as defined in the guidelines on the management of POP waste of the Basel Convention. The concentrations of Ʃ14 PCBs in the soils were above the Dutch guideline value of 1000 μg kg⁻¹ and the estimated incremental lifetime cancer risks relating to exposure of humans to PCBs in soils indicate serious health risks. There is therefore a need to implement a surveillance programme in the vicinity of power plants to determine the impacts on the adjacent ecosystem.

Brominated flame retardants and dechlorane plus on a remote high mountain of the eastern Tibetan Plateau: implications for regional sources and environmental behaviors

We investigated the occurrence of halogenated flame retardants (HFRs) including polybrominated diphenyl ethers (PBDEs), six novel brominated flame retardants (NBFRs) and dechlorane plus in air and soils on the eastern slope of Mt. Gongga on the eastern Tibetan Plateau. We detected all of the NBFR except bis(2-ethylhexyl)-tetrabromophthalate and pentabromoethyl benzene. NBFRs constituted the most prevalent group. BDE-28 and BDE-47 dominated among the PBDE congeners. Decabromodiphenyl ethane was detected at relatively high levels up to 171 pg/m³ and 1450 pg/g dry weight in air and soils, respectively; however, it appeared to be easily degraded in the environment. A general decreasing trend was observed among the HFR concentrations with increasing altitude, and this was due to the prominent contribution of source emissions over possible influence of environmental conditions. This study also suggests that HFRs are supplied to forest soils mainly in the form of precipitation and retained in the O horizon layers.

Persistent organic pollutant emission via dust deposition throughout Pakistan: Spatial patterns, regional cycling and their implication for human health risks

In the current study, Persistent Organic Pollutants (POPs) in outdoor dustfall was monitored for the first time along the Indus river system of Pakistan. Among the studied OCPs (ng/g, dry weight), DDTs (0.16-62) were the predominant contaminants identified in deposited dust followed by HCHs (0.1-10.2), HCB (0.09-7.4) and chlordanes (0.1-2.8). The indicative diagnostic ratio for DDTs and HCHs suggested recent emission of DDTs as well as historical emission of both chemicals in regions where they were used for crop protection and malarial control. The levels of ∑₃₁PCBs (ng/g, dry weight) in dust ranged from 0.95-125, and compositional profiles suggested arochlor-1248, -1254 commercial mixtures as source. A few exceptions were samples from urban areas that reflected the use of aroclor-1260, and-1262 and/or unintentional leakage from several industrial processes. The WHO₀₅-TEQ values for dioxin-like PCBs (with major contributions of PCB-126) were found to be 0.07-34.5 (median; 1.87) pg TEQg^-1dw for all the studied samples. Correlation analysis identified that DDTs, HCHs, HCB and PCBs were significantly associated (r=90; p<0.01) with dusts collected in proximity to urban centers with widespread anthropogenic activities in these areas. A few cases where high levels of POPs from remote mountain highlands were detected, point to the potential for long range transport of these chemicals. Human risk assessment analysis of contaminated dust showed that DDTs and PCBs are major constituent chemicals of concern with regard to the development of cancer in children, with ingestion being the main route of exposure of dust-borne DDTs (0.12-1.03×10^-6) and PCBs (0.86-12.43×10^-6).

Polychlorinated biphenyls and polybrominated diphenylethers in soils from planted forests and adjacent natural forests on a tropical island

Transformation from natural forests to planted forests in tropical regions is an expanding global phenomenon causing major modifications of land cover and soil properties, e.g. soil organic carbon (SOC). This study investigated accumulations of POPs in soils under eucalyptus and rubber forests as compared with adjacent natural forests on Hainan Island, China. Results showed that due to the greater forest filter effect and the higher SOC, the natural forest have accumulated larger amounts of POPs in the top 20 cm soil. Based on correlation and air-soil equilibrium analysis, we highlighted the importance of SOC in the distribution of POPs. It is assumed that the elevated mobility of POPs in the planted forests was caused by greater loss of SOC and extensive leaching in the soil profile. This suggests that a better understanding of global POPs fate should take into consideration the role of planted forests.

Polycyclic aromatic hydrocarbons (PAHs) in Chinese forest soils: profile composition, spatial variations and source apportionment

Previous studies reported that forest ecosystems can play a vital role in scavenging anthropogenic polycyclic aromatic hydrocarbons (PAHs) and act as primary reservoirs of these environmental pollutants. The present study aimed to investigate the occurrence, spatial pattern and source apportionment of PAHs across Chinese background forest soils (O- & A-horizons). The 143 soils collected from 30 mountains showed significantly (p < 0.05) higher levels of ∑₁₅PAHs (ng g⁻¹ dw) in O-horizon (222 ± 182) than A-horizon (168 ± 161). A progressive increase in the levels of lighter PAHs was observed along altitudinal gradient, however heavier PAHs did not show any variations. Carbon contents (TOC & BC) of forest soils were found weakly correlated (p < 0.01) with low molecular weight (LMW)-PAHs but showed no relation with high molecular weight (HMW)-PAHs. Source apportionment results using PMF and PCA revealed that PAHs in forest soils mainly come from local biomass burning and/or coal combustion and attributed that forest soils may become a potential sink for PAHs in the region.

Long-Term Temporal Trends of Polychlorinated Biphenyls and Their Controlling Sources in China

Polychlorinated biphenyls (PCBs) are industrial organic contaminants identified as persistent, bioaccumulative, toxic (PBT), and subject to long-range transport (LRT) with global scale significance. This study focuses on a reconstruction and prediction for China of long-term emission trends of intentionally and unintentionally produced (UP) ∑₇PCBs (UP-PCBs, from the manufacture of steel, cement and sinter iron) and their re-emissions from secondary sources (e.g., soils and vegetation) using a dynamic fate model (BETR-Global). Contemporary emission estimates combined with predictions from the multimedia fate model suggest that primary sources still dominate, although unintentional sources are predicted to become a main contributor from 2035 for PCB-28. Imported e-waste is predicted to play an increasing role until 2020-2030 on a national scale due to the decline of intentionally produced (IP) emissions. Hypothetical emission scenarios suggest that China could become a potential source to neighboring regions with a net output of ∼0.4 t year^-1 by around 2050. However, future emission scenarios and hence model results will be dictated by the efficiency of control measures.

Impacts of Large-Scale Land-Use Change on the Uptake of Polycyclic Aromatic Hydrocarbons in the Artificial Three Northern Regions Shelter Forest Across Northern China

This study quantifies the influence of large-scale land-use change induced by the artificial Three-Northern Regions Shelter Forest (TNRSF) across northern China on the environmental cycling of organic chemicals. Atmospheric removal and long-term trends of two polycyclic aromatic hydrocarbon (PAH) species, phenanthrene (PHE) and benzo[a]pyrene (BaP), resulting from increasing vegetation coverage and soil organic carbon in the TNRSF over the last two decades were examined. Field sampling data and modeling result showed that the total atmospheric removal of PHE by TNRSF increased from 36.4 tons in 1990 to 76.8 tons in 2010, increasing at a rate of 5.6% yr^-1, and BaP from 2.2 to 4.5 tons, increasing at a rate of 5.2% yr^-1. Three model scenarios were designed to distinguish the effects of atmospheric emissions, and with and without TNRSF on the environmental fate of PAHs. Approximately 1-4% of PHE and BaP emitted in northern China were removed by the TNRSF during 1990-2010. Model simulations revealed that the TNRSF enhanced atmospheric removal of PHE by 29% and BaP by 53% compared with the simulation without the TNRSF, manifesting marked contributions of land-use change by the artificial TNRSF, the largest afforestation activity in human history, to the atmospheric removal of organic chemicals.

Research on persistent organic pollutants in China on a national scale: 10 years after the enforcement of the Stockholm Convention

As a signatory of the Stockholm Convention and the largest developing country, China plays a very important role in implementation of the convention to reduce and finally eliminate persistent organic pollutants (POPs) in the world. In the past ten years after the enforcement in 2004, Chinese Government and scientists have made great progress on the study of POPs. The present work aims to provide an overview on recent studies on POPs in China, with particular focus on usage/emission inventory, residue inventory, and pollution status of POPs on national scale. Several legend (old) and new target POPs were comprehensively summarized with progress on inventory. Furthermore, several national scale monitoring programs have been selected for the occurrence, spatial and temporal trends of POPs in China, which are compared with Asian data and Global data. Based on the observed results, some important scientific issues, such as the primary and secondary distribution patterns, the primary and secondary fractionations, and air-soil exchange of POPs, are also discussed. It is proposed that more studies should be carried out for the new targeted POPs in future for both the national and global interests.

Spatial distribution of dust-bound trace elements in Pakistan and their implications for human exposure

This study aims to assess the spatial patterns of selected dust-borne trace elements alongside the river Indus Pakistan, their relation with anthropogenic and natural sources, and the potential risk posed to human health. The studied elements were found in descending concentrations: Mn, Zn, Pb, Cu, Ni, Cr, Co, and Cd. The Index of Geo-accumulation indicated that pollution of trace metals were higher in lower Indus plains than on mountain areas. In general, the toxic elements Cr, Mn, Co and Ni exhibited altitudinal trends (P < 0.05). The few exceptions to this trend were the higher values for all studied elements from the northern wet mountainous zone (low lying Himalaya). Spatial PCA/FA highlighted that the sources of different trace elements were zone specific, thus pointing to both geological influences and anthropogenic activities. The Hazard Index for Co and for Mn in children exceeded the value of 1 only in the riverine delta zone and in the southern low lying zone, whereas the Hazard Index for Pb was above the bench mark for both children and adults (with few exceptions) in all regions, thus indicating potential non-carcinogenic health risks. These results will contribute towards the environmental management of trace metal(s) with potential risk for human health throughout Pakistan.

Polychlorinated biphenyls (PCBs) in sediments/soils of different wetlands along 100-year coastal reclamation chronosequence in the Pearl River Estuary, China

PCBs (polychlorinated biphenyls) were determined in sediment/soil profiles to a depth of 30 cm from three different wetlands (i.e., ditch wetlands, riparian wetlands and reclaimed wetlands) of the Pearl River Estuary to elucidate their levels, distribution and toxic risks along a 100-year chronosequence of reclamation. All detected PCB congeners and the total 15 PCBs (∑15 PCBs) decreased with depth along sediment/soil profiles in these three wetlands. The ∑15 PCBs concentrations ranged from 17.68 to 169.26 ng/g in surface sediments/soils. Generally, old wetlands tended to have higher PCB concentrations than younger ones. The dominant PCB congeners at all sampling sites were light PCB homologues (i.e., tetra-CBs and tri-CBs). According to the sediment quality guideline, the average PCB concentrations exceeded the threshold effects level (TEL, 21.6 ng/g) at most of the sampling sites, exhibiting possible adverse biological effects, which were dominantly caused by light PCB congeners. The total toxic equivalent (TEQ) concentrations of 10 dioxin-like PCBs (DL-PCBs) detected at all sampling sites ranged from 0.04 to 852.7 (10(-3) ng/g), mainly affected by PCB126. Only DL-PCB concentrations in ditch and riparian wetland sediments with 40-year reclamation histories (i.e., D40 and Ri40) exhibited moderate adverse biological effects according to SQGQ values. Principal component analysis indicated that PCBs in three wetland sediments/soils mainly originated from Aroclor 1016, 1242, and 1248. Correlation analysis showed that sediment/soil organic carbon content had a significant correlation with the concentrations of several PCB congeners (P < 0.05), whereas no significant correlations were observed between any PCBs congeners and grain size or aggregate content (P > 0.05).

Bacteria capable of degrading anthracene, phenanthrene, and fluoranthene as revealed by DNA based stable-isotope probing in a forest soil

Information on microorganisms possessing the ability to metabolize different polycyclic aromatic hydrocarbons (PAHs) in complex environments helps in understanding PAHs behavior in natural environment and developing bioremediation strategies. In the present study, stable-isotope probing (SIP) was applied to investigate degraders of PAHs in a forest soil with the addition of individually (13)C-labeled phenanthrene, anthracene, and fluoranthene. Three distinct phylotypes were identified as the active phenanthrene-, anthracene- and fluoranthene-degrading bacteria. The putative phenanthrene degraders were classified as belonging to the genus Sphingomona. For anthracene, bacteria of the genus Rhodanobacter were the putative degraders, and in the microcosm amended with fluoranthene, the putative degraders were identified as belonging to the phylum Acidobacteria. Our results from DNA-SIP are the first to directly link Rhodanobacter- and Acidobacteria-related bacteria with anthracene and fluoranthene degradation, respectively. The results also illustrate the specificity and diversity of three- and four-ring PAHs degraders in forest soil, contributes to our understanding on natural PAHs biodegradation processes, and also proves the feasibility and practicality of DNA-based SIP for linking functions with identity especially uncultured microorganisms in complex microbial biota.

Human Arsenic exposure via dust across the different ecological zones of Pakistan

The present study aims to assess the arsenic (As) levels into dust samples and its implications for human health, of four ecological zones of Pakistan, which included northern frozen mountains (FMZ), lower Himalyian wet mountains (WMZ), alluvial riverine plains (ARZ), and low lying agricultural areas (LLZ). Human nail samples (N=180) of general population were also collected from the similar areas and all the samples were analysed by using ICP-MS. In general the higher levels (p<0.05) in paired dust and human nail samples were observed from ARZ and LLZ than those of other mountainous areas (i.e., WMZ and FMZ), respectively. Current results suggested that elevated As concentrations were associated to both natural, (e.g. geogenic influences) and anthropogenic sources. Linear regression model values indicated that As levels into dust samples were associated with altitude (r(2)=0.23), soil carbonate carbon density (SCC; r(2)=0.33), and population density (PD; r(2)=0.25). The relationship of paired dust and nail samples was also investigated and associations were found for As-nail and soil organic carbon density (SOC; r(2)=0.49) and SCC (r(2)=0.19) in each studied zone, evidencing the dust exposure as an important source of arsenic contamination in Pakistan. Risk estimation reflected higher hazard index (HI) values of non-carcinogenic risk (HI>1) for children populations in all areas (except FMZ), and for adults in LLZ (0.74) and ARZ (0.55), suggesting that caution should be paid about the dust exposure. Similarly, carcinogenic risk assessment also highlighted potential threats to the residents of LLZ and ARZ, as in few cases (5-10%) the values exceeded the range of US-EPA threshold limits (10(-6)-10(-4)).

Polychlorinated naphthalenes (PCNs) in Chinese forest soil: Will combustion become a major source?

We collected O- and A-horizon soil samples in 26 Chinese mountainous forests to investigate the content, spatial pattern, and potential sources of polychlorinated naphthalenes (PCNs). Spatial patterns were influenced mainly by the approximation to sources and soil organic contents. High concentrations often occurred close to populated or industrialized areas. Combustion-related activities contributed to PCN pollution. Relatively high proportions of CN-73 in northern China may be attributed to coke consumption, while CN-51 could be an indicator of biomass burning in Southwest China. There are evidences that PCNs may largely derived from unintentional production. If uncontrolled, UP-PCN (unintentionally produced PCNs) emissions could increase with industrial development. The abnormally high concentrations at Gongga and Changbai Mountains appear to be associated with the high efficient of forest filter of atmospheric contaminants at these densely forested sites. We question whether this is caused by ecotones between forests, and raise additional questions for future analyses.

Elevated mobility of persistent organic pollutants in the soil of a tropical rainforest

Semivolatile persistent organic pollutants (POP) are bioaccumulative and toxic contaminants. Their global distribution depends on source distribution, atmospheric transport, degradation, and the exchange with ocean and land surfaces. Forests are crucial terrestrial reservoirs due to the commonly envisaged high capacity of their surface soils to store and immobilize airborne contaminants bound to soil organic matter. Our results show that POPs can be unexpectedly mobile in the soil of a tropical rainforest due to fast litter turnover (leading to rapid POP transfer to the subsoil) and leaching rates exceeding degradation rates especially for more hydrophobic congeners. Co-transport in association with leaching fine particulate and dissolved organic matter appears as a relevant driver of this PCB export. A markedly different distribution pattern is displayed in this soil in comparison to soils of colder environments with lower overall storage capacity. These findings show that biogeochemistry of organic matter degradation and weathering can influence POP soil fate. Because tropical forests represent 60% of the global terrestrial productivity, the highlighted dynamics might have an implication for the general distribution of these contaminants.

Spatial distribution of old and emerging flame retardants in Chinese forest soils: sources, trends and processes

The levels and distribution of polybrominated diphenylethers (PBDEs), novel brominated flame retardants (NBFRs) and Dechlorane Plus (DP) in soils and their dependence on environmental and anthropological factors were investigated in 159 soil samples from 30 background forested mountain sites across China. Decabromodiphenylethane (DBDPE) was the most abundant flame retardant (25-18,000 pg g(-1) and 5-13,000 pg g(-1) in O-horizon and A-horizon, respectively), followed by BDE 209 (nd-5900 pg g(-1) and nd-2400 pg g(-1) in O-horizon and A-horizon, respectively). FRs distributions were primarily controlled by source distribution. The distributions of most phasing-out PBDEs, DP isomers and TBPH were in fact correlated to a population density-based index used as proxy of areas with elevated usage and waste of FR containing products. High concentrations of some NBFRs were however observed in industrialized regions and FR manufacturing plants. Strongly positive correlations were observed between PBDEs and their replacement products suggesting similar emission pattern and environmental behavior. Exposure of mineral subsoils depended on precipitations driving leaching of FRs into the soil core. This was especially evident for some emerging BFRs (TBE, TBPH, and TBB etc.) possibly indicating potential for diffuse groundwater contamination.