Jianteng Sun

Contamination of phthalate esters, organochlorine pesticides and polybrominated diphenyl ethers in agricultural soils from the Yangtze River Delta of China.

To reveal the pollution status associated with rapid urbanization and economic growth, extensive areas of agricultural soils (approximately 45,800 km(2)) in the Yangtze River Delta of China were investigated with respect to selected endocrine disruptor compounds (EDCs), including phthalate esters (PAEs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs). The residues of sum of 15 PAEs, sum of 15 OCPs and sum of 13 PBDEs were in the range of 167-9370 ng/g, 1.0-3520 ng/g, and <1.0-382 ng/g, respectively. The OCPs residuals originated from both historical usage and recent input. Agricultural plastic film was considered to be an important source of PAEs. Discharge from furniture industry was potential major source of PBDEs in this region. The selected pollutants showed quite different spatial distributions within the studied region. It is worth noting that much higher concentrations of the EDCs were found on the borders between Shanghai and the two neighboring provinces, where agriculture and industry developed rapidly in recent years. Contaminants from both agricultural and industrial activities made this area a pollution hotspot, which should arouse more stringent regulation to safeguard the environment and food security.

Organic contamination and remediation in the agricultural soils of China: A critical review

Soil pollution is a global problem in both developed and developing countries. Countries with rapidly developing economies such as China are faced with significant soil pollution problems due to accelerated industrialization and urbanization over the last decades. This paper provides an overview of published scientific data on soil pollution across China with particular focus on organic contamination in agricultural soils. Based on the related peer-reviewed papers published since 2000 (n=203), we evaluated the priority organic contaminants across China, revealed their spatial and temporal distributions at the national scale, identified their possible sources and fates in soil, assessed their potential environmental risks, and presented the challenges in current remediation technologies regarding the combined organic pollution of agricultural soils. The primary pollutants in Northeast China were polycyclic aromatic hydrocarbons (PAHs) due to intensive fossil fuel combustion. The concentrations of organochlorine pesticides (OCPs) and phthalic acid esters (PAEs) were higher in North and Central China owing to concentrated agricultural activities. The levels of polychlorinated biphenyls (PCBs) were higher in East and South China primarily because of past industrial operations and improper electronic waste processing. The co-existence of organic contaminants was severe in the Yangtze River Delta, Pearl River Delta, and Beijing-Tianjin-Hebei Region, which are the most populated and industrialized regions in China. Integrated biological-chemical remediation technologies, such as surfactant-enhanced bioremediation, have potential uses in the remediation of soil contaminated by multiple contaminants. This critical review highlighted several future research directions including combined pollution, interfacial interactions, food safety, bioavailability, ecological effects, and integrated remediation methods for combined organic pollution in soil.

Detection of methoxylated and hydroxylated polychlorinated biphenyls in sewage sludge in China with evidence for their microbial transformation.

The concentrations of methoxylated polychlorinated biphenyls (MeO-PCBs) and hydroxylated polychlorinated biphenyls (OH-PCBs) were measured in the sewage sludge samples collected from twelve wastewater treatment plants in China. Two MeO-PCB congeners, including 3′-MeO-CB-65 and 4′-MeO-CB-101, were detected in three sludge with mean concentrations of 0.58 and 0.52 ng/g dry weight, respectively. OH-PCBs were detected in eight sludge samples, with an average total concentration of 4.2 ng/g dry weight. Furthermore, laboratory exposure was conducted to determine the possible source of OH-PCBs and MeO-PCBs in the sewage sludge, and their metabolism by the microbes. Both 4′-OH-CB-101 and 4′-MeO-CB-101 were detected as metabolites of CB-101 at a limited conversion rate after 5 days. Importantly, microbial interconversion between OH-PCBs and MeO-PCBs was observed in sewage sludge. Demethylation of MeO-PCBs was favored over methylation of OH-PCBs. The abundant and diverse microbes in sludge play a key role in the transformation processes of the PCB analogues. To our knowledge, this is the first report on MeO-PCBs in environmental matrices and on OH-PCBs in sewage sludge. The findings are important to understand the environmental fate of PCBs.

Uptake, translocation, and metabolism of hydroxylated and methoxylated polychlorinated biphenyls in maize, wheat, and rice

Hydroxylated polychlorinated biphenyls (OH-PCBs) have been found in the environment with high toxicity. Recently, methoxylated polychlorinated biphenyls (MeO-PCBs) were identified as new pollutants and detected in sewage sludge. This study presents a detailed investigation on the uptake, translocation, and metabolism of OH-PCBs and MeO-PCBs in typical crops including maize, wheat, and rice. The interconversion between OH-PCBs and MeO-PCBs were observed. Demethylation of MeO-PCBs was favored over methylation of OH-PCBs. The metabolites were mainly generated in the roots and then translocated to the shoots. Analog-specific differences showed that the accumulation amounts of MeO-PCBs were higher than those of OH-PCBs in the crops. The translocation abilities followed this order: 3′-OH-CB-65 > 4′-OH-CB-101 > 3′-MeO-CB-65 > 4′-MeO-CB-101. The conversion rates were generally higher for 4′-OH-CB-101 than 3′-OH-CB-65 and higher for 4′-MeO-CB-101 than 3′-MeO-CB-65. Interspecies variability among the crops was also observed. The amounts of metabolites and acropetal translocation inside the plants were the greatest for maize. However, the concentration of compounds normalized by the mass of corresponding plant tissue was highest in wheat. These findings provide valuable information for a better understanding of the phytoaccumulation and phytotransformation of OH-PCBs and MeO-PCBs.

Formation of hydroxylated and methoxylated polychlorinated biphenyls by Bacillus subtilis: New insights into microbial metabolism

The detoxification and degradation of polychlorinated biphenyls (PCBs) have been studied. However, little information is available about the biological mechanisms involved in the metabolism of hydroxylated polychlorinated biphenyls (OH-PCBs) and methoxylated polychlorinated biphenyls (MeO-PCBs) by specific microorganism. In this study, the simultaneous formation of OH-PCB (major metabolite) and MeO-PCB (minor metabolite) was found in Bacillus subtilis after exposure to PCB. Interconversion between MeO-PCB and OH-PCB was also observed and the demethylation ratio of MeO-PCB was higher than the methylation ratio of OH-PCB. The high-throughput RNA-sequencing (RNA-Seq) was conducted to analyze the genes involved in the metabolism processes. The potential metabolism pathways of PCB by Bacillus subtilis were proposed. PCB can be transformed to OH-PCB by Cytochrome P450 encoded by the genes bioI and cypA. The genes ycgJ and ycgI that are related with methyltransferase are potentially involved in the subsequent biotransformation from OH-PCB to MeO-PCB. MeO-PCB was prone to be transformed to OH-PCB by a group of hydrolases. This is the first study considering the mechanism involved in the interconversion between OH-PCBs and MeO-PCBs by microorganism. These findings broaden our insights into the biotransformation mechanism of PCBs in the environment.

Transformation of hydroxylated and methoxylated 2,2′,4,4′,5-brominated diphenyl ether (BDE-99) in plants

The occurrence and fate of hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) have received significant attention. However, there is limited information on the metabolism relationship between OH-pentaBDEs and MeO-pentaBDEs that were frequently detected with relatively high concentrations in the environment. In this study, the biotransformation between OH-BDE-99 and MeO-BDE-99 was investigated in rice, wheat, and soybean plants. All the three plants can metabolize OH-BDE-99 to corresponding homologous methoxylated metabolites, while the transformation from MeO-BDE-99 to OH-BDE-99 could only be found in soybean. The conversion of parent compounds was the highest in soybean, followed by wheat and rice. Transformation products were found mainly in the roots, with few metabolites being translocated to the shoots and solution after exposure. The results of this study provide valuable information for a better understanding of the accumulation and transformation of OH-PBDEs and MeO-PBDEs in different plants.

Multimedia modeling of the PAH concentration and distribution in the Yangtze River Delta and human health risk assessment

Emissions of polycyclic aromatic hydrocarbons (PAHs) in China remain at a high level compared to those in developed countries. The Yangtze River Delta (YRD) is an economic and industrial center in China with an extremely large population. The potentially high emissions and excess cancer risk from human exposure in this region cannot be neglected. This study applied a multimedia model to estimate the concentrations of 16 US EPA priority PAHs in the environment in the YRD with a well-developed PAH-emission inventory for 2014. The model predicted that the average concentrations of ΣPAHs were 274 ng/m3 in the air, 255 ng/g in the soil, 15 ng/g in vegetation, 147 ng/L in freshwater and 144 ng/g in sediment, as well as 99 ng/L and 80 ng/g in seawater and sediment, respectively. Soil is the PAH sink in this region, and the net flux of the total PAHs is always from air to soil for each isomer. A deterministic assessment observed that the ELCR (excess lifetime cancer risk) ranged from 2.5 × 10-6 to 3.0 × 10-5 for exposure by air inhalation and from 3.5 × 10-7 to 7.9 × 10-6 for exposure by soil ingestion. The probabilistic results did not find any probability of ELCR >10-4 by exposure via soil ingestion in the YRD. The probabilistic ELCR induced by inhalation exposure varied from 8.1 × 10-7 to 3.1 × 10-4 in the YRD. This study provided a comprehensive overview of PAHs occurrence in natural environments and of the relevant human health risks. The information presented in this study could help authorities to enact a strategy regarding emission reduction and pollution control relevant to PAHs. CAPSULE Multimedia modeling predicted distributions and compositions of PAHs in different environmental compartments, and deterministic and probabilistic ELCRs induced by air inhalation and soil ingestion were also provided.

The role of artificial root exudate components in facilitating the degradation of pyrene in soil

Root exudates play an important role in the phytoremediation of soils contaminated by organic pollutants, but how root exudate components affect the remediation process is not well understood. In this study, we explored the effects and mechanisms of the major root exudates, including glucose, organic acids, and serine, in the rhizoremediation of pyrene-contaminated soil. The results showed that glucose increased the degradation of pyrene (54.3 ± 1.7%) most significantly compared to the organic acids (45.5 ± 2.5%) and serine (43.2 ± 0.1%). Glucose could significantly facilitate the removal of pyrene in soil through promoting dehydrogenase activity indicated by a positive correlation between the removal efficiency of pyrene and the soil dehydrogenase activity (p < 0.01). Furthermore, root exudates were able to change soil microbial community, particularly the bacterial taxonomic composition, thereby affecting the biodegradation of pyrene. Glucose could alter soil microbial community and enhance the amount of Mycobacterium markedly, which is dominant in the degradation of pyrene. These findings provide insights into the mechanisms by which root exudates enhance the degradation of organic contaminants and advance our understanding of the micro-processes involved in rhizoremediation.

Comparison of greenhouse and open field cultivations across China: Soil characteristics, contamination and microbial diversity

A national scale survey was conducted to determine an array of inorganic and organic contaminants in agricultural soils from two cultivation modes (greenhouse vs. open field) in 20 provinces across China. The investigated contaminants include organochlorine pesticides (OCPs), phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), lead (Pb), zinc (Zn), copper (Cu) and cadmium (Cd). The large amounts of agrochemicals used and special cultivation mode in greenhouse caused substantial soil pollution and deterioration of soil quality. Mean concentrations of both OCPs and PAEs in greenhouse soil were approximately 100% higher than those in open field. The pH values were 6.85 ± 1.04 and 7.34 ± 0.84 for greenhouse and open field, respectively (p > 0.05). The soil microbial community was predicted to be affected by pollution in greenhouse through the PICRUSt analysis of 16s rRNA sequences. The 12 variables including various chemicals and soil properties together explained 15% of the observed variation in the community composition. In the studied variables, PAEs and lead were the primary factors affecting microbial diversity in greenhouse soils, while pH had the greatest impact on the microbial community in open field soils. These findings enhanced our understanding of the environmental impact and contamination management of greenhouses worldwide.