The bioaccessibility of organic pollutants is a key factor in human health risk assessments. We developed a novel in vitro method for determining the mass fraction of bioaccessible atmospheric polycyclic aromatic hydrocarbons (PAHs) using an air-washing device containing simulated human lung fluid. The experimental parameters were optimized based on the deposition fractions (DFs) of PAHs in human lung fluids. The DFs were measured for PAHs based on the mass of compounds in the mainstream and exhaled cigarette smoke. The mass fractions of bioaccessible PAHs were measured by passing the mainstream cigarette smoke through the air-washing device, and they were calculated via a simple mass balance equation based on the PAHs in the fluid and mainstream cigarette smoke. The DFs of individual PAHs ranged from 20.5% to 78.1%, and the bioaccessible mass fractions varied between 45.5% and 99.8%. The octanol-water partition coefficients (KOW) significantly influenced both the DFs and bioaccessible mass fractions of PAHs, and the optimized in vitro method could be used to estimate the bioavailable atmospheric PAHs. This in vitro method can potentially be used to measure the mass fraction of bioaccessible atmospheric PAHs and to assess the health risk related to human exposure to airborne PAHs.

Given the sub-lethal risks of synthetic surfactants, rhamnolipid is a promising class of biosurfactants with the potential to promote the bioavailability of polycyclic aromatic hydrocarbons (PAHs), to provide a favorable substitute for synthetic surfactants. However, few previous studies have integrated the behavior and mechanism behind rhamnolipid-influenced PAH biosorption and biodegradation. This is, to our knowledge, the first report of a bacterial envelope regulated link between phenanthrene (PHE) biosorption and biodegradation by rhamnolipid-induced PHE-degrading strain Pseudomonas sp. Ph6. Rhamnolipid (0─400 mg L−1) can change the cell-surface zeta potential, cell surface hydrophobicity (CSH), cell ultra-microstructure and functional groups, and then alter PHE biosorption and biodegradation of Ph6. Greater amounts of PHE sorbed on cell envelopes results in more PHE diffusing into cytochylema, thus favoring PHE intracellular biodegradation of Ph6. Rhamnolipid (≤100 mg L−1) could change the microstructures and functional groups of cell envelopes of Ph6, enhance the cell-surface zeta potential and CSH, thus consequently favor PHE biosorption and biodegradation by strain Ph6. By contrast, rhamnolipid at higher concentrations (≥200 mg L−1) hindered PHE biosorption and biodegradation. Rhamnolipid, as a biosurfactant, can be successfully utilized as an additive to improve the microbial biodegradation of PAHs in the environments.

Using hybrid packing materials in biofiltration systems takes advantage of both the inorganic and organic properties offered by the medium including structural stability and a source of available nutrients, respectively. In this study, hybrid mixtures of compost with either lava rock or biochar in four different mixture ratios were compared against 100% compost in a methane biofilter with active aeration at two ports along the height of the biofilter. Biochar outperformed lava rock as a packing material by providing the added benefit of participating in sorption reactions with CH4. This study provides evidence that a 7:1 volumetric mixture of biochar and compost can successfully remove up to 877 g CH4/m3·d with empty-bed residence times of 82.8 min. Low-affinity methanotrophs were responsible for the CH4 removal in these systems (KM(app) ranging from 5.7 to 42.7 µM CH4). Sequencing of 16S rRNA gene amplicons indicated that Gammaproteobacteria methanotrophs, especially members of the genus Methylobacter, were responsible for most of the CH4 removal. However, as the compost medium was replaced with more inert medium, there was a decline in CH4 removal efficiency coinciding with an increased dominance of Alphaproteobacteria methanotrophs like Methylocystis and Methylocella. As a biologically-active material, compost served as the sole source of nutrients and inoculum for the biofilters which greatly simplified the operation of the system. Higher elimination capacities may be possible with higher compost content such as a 1:1 ratio of either biochar or lava rock, while maintaining the empty-bed residence time at 82.8 min.

Plastic pollution is a major global concern with several million microplastic particles entering every day freshwater ecosystems via wastewater discharge. Microplastic particles stimulate biofilm formation (plastisphere) throughout the water column and have the potential to affect microbial community structure if they accumulate in pelagic waters, especially enhancing the proliferation of biohazardous bacteria. To test this scenario, we simulated the inflow of treated wastewater into a temperate lake using a continuous culture system with a gradient of concentration of microplastic particles. We followed the effect of microplastics on the microbial community structure and on the occurrence of integrase 1 (int1), a marker associated with mobile genetic elements known as a proxy for anthropogenic effects on the spread of antimicrobial resistance genes. The abundance of int1 increased in the plastisphere with increasing microplastic particle concentration, but not in the water surrounding the microplastic particles. Likewise, the microbial community on microplastic was more similar to the original wastewater community with increasing microplastic concentrations. Our results show that microplastic particles indeed promote persistence of typical indicators of microbial anthropogenic pollution in natural waters, and substantiate that their removal from treated wastewater should be prioritised.

Organochlorine pesticides (OCPs), including dichlorodiphenyltrichloroethane (DDT) and its metabolites [dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane], hexachlorocyclohexanes (HCHs), and hexachlorobenzene (HCB), are widely detected in humans despite the considerable decline in environmental concentrations. To understand the placental transfer of OCPs and the possible maternal influence on them, we measured the concentrations of DDTs, HCHs, and HCB in 102 paired samples of maternal and cord sera, and placentas collected in Shanghai, China. The median concentrations of DDTs and HCHs were the highest in maternal sera (601, 188 ng g⁻¹ lipid), followed by umbilical cord sera (389, 131 ng g⁻¹ lipid), and placentas (65, 37 ng g⁻¹ lipid). 4,4′-DDE, β-HCH, and HCB were the predominant contaminants in the three matrices. The ubiquitous existence of OCPs, and the significant concentration relationships of DDTs, HCHs, and OCPs in the three matrices suggested placental transfer from mother to fetus. The lipid-based concentration ratios of 4,4′-DDE, β-HCH, and HCB in umbilical cord serum to those in maternal serum (F/M), and ratios of placenta to maternal serum (P/M) ranged from 0.66 to 1.01, and 0.12 to 0.25, respectively. Maternal variables affected the levels of fetal contamination. For primiparous women, significant correlations between maternal age and maternal HCHs, and between pre-pregnancy body mass index (BMI) and maternal HCHs were found. The negative effect of parity, and the positive effect of food consumption on maternal OCP concentrations were also observed, although there were no significant differences. The possible influence of parity on F/M and P/M of 4,4′-DDE suggested borderline significant differences between primiparous and multiparous women. Also, slight group differences were observed between elder and younger women, and between overweight and normal/underweight women. Parity seems to have a potential influence on transfer ratios of some OCP pollutants.

The aim of this study was to assess, for the first time, the concentrations, sources, dry deposition and human health risks of polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in total suspended particle (TSP) samples collected in Bizerte city, Tunisia (North Africa), during one year (March 2015–January 2016). Concentrations of PAHs, AHs, PCBs and OCPs ranged 0.5–17.8 ng m−3, 6.7–126.5 ng m−3, 0.3–11 pg m−3 and 0.2–3.6 pg m−3, respectively, with higher levels of all contaminants measured in winter. A combined analysis revealed AHs originating from both biogenic and petrogenic sources, while diesel vehicle emissions were identified as dominant sources for PAHs. PCB potential sources included electronic, iron, cement, lubricant factories located within or outside Bizerte city. The dominant OCP congeners were p,p′-DDT and p,p′-DDE, reflecting a current or past use in agriculture. Health risk assessment showed that the lifetime excess cancer risk from exposure to airborne BaP was negligible in Bizerte, except in winter, where a potential risk to the local population may occur.

Greenhouse vegetable production (GVP) is the major type of vegetable production in China. However, dietary exposure of heavy metals through vegetable consumption has been identified as a potential risk to human health. To ensure safety of vegetables, soil threshold values (STVs) of cadmium (Cd) in GVP systems were assessed based on analysis of soil-vegetable Cd contents in relation to human health risk. Contents of Cd were determined in 324 sampled soil-vegetable pairs from five GVP systems in three Chinese provinces. Soil Cd contents ranged from 0.07 to 1.32 mg kg−1, with 17.9% of sampled soils exceeding current Chinese threshold values. Vegetable Cd contents ranged from 0.0003 to 0.546 mg kg−1, with 8.6% exceeding permissible maxima. Vegetable type and soil pH significantly affected Cd transfer from soil to vegetable with lower transfer at neutral (6.5 < pH ≤ 7.5) to alkaline (pH > 7.5) soils and uptake decreasing in the order: Leafy > rootstalk > fruit. Consequently, both soil pH and vegetable type should be taken into consideration as suggested when revising current STVs for Cd in GVP systems in order to capture the health risk correctly and ensure safe vegetable consumption.

Cometabolism mechanisms of organic pollutants in environmental microbes have not been fully understood. In this study, a global analysis of Mycobacterium sp. strain A1-PYR transcriptomes on different PAH substrates (single or binary of pyrene (PYR) and phenanthrene (PHE)) was conducted. Comparative results demonstrated that expression levels of 23 PAH degradation enzymes were significantly higher in the binary substrate than in the PYR-only one. These enzymes constituted an integrated enzymatic system to actualize all transformation steps of PYR, and most of their encoded genes formed a novel gene cascade in the genome of strain A1-PYR. The roles of different genotypes of enzymes in PYR cometabolism were also discriminated even though all of their gene sequences were presented in the genome of this strain. NidAB and PdoA2B2 instead of NidA3B3 served the initial oxidization of PAHs, and PcaL replaced PcaCD to catalyze the formation of 3-oxoadipate. Novel genes associated with PYR cometabolism was also predicted by the relationships between their transcription profiles and PYR removal. The results showed that ABC-type transporters probably played important roles in the transport of PAHs and their metabolites through cell membrane, and [4Fe-4S] ferredoxin might be essential for dioxygenases (NidAB and PdoA2B2) to achieve oxidative activities. This study provided molecular insight in that microbial degrader subtly cometabolized recalcitrant PAHs with relatively more degradable ones.

Carbamazepine (CBZ) is an antiepileptic drug that is frequently detected in wastewater treatment plants, soil and plants after irrigation with treated wastewater or application of biosolids. However, little information is available on the fate and uptake of CBZ in edible vegetables. In this study, radioautographic visualization of the ¹⁴C distribution revealed that ¹⁴C-CBZ can be taken up by all three ready-to-eat vegetables. Furthermore, a mass-balance study was conducted to evaluate the dynamic processes of the uptake and translocation of CBZ by ¹⁴C labeling. ¹⁴C-CBZ was gradually taken up with the growth of vegetables, with maximum uptake ratios of 2.19 ± 0.15, 2.86 ± 0.24 and 0.25 ± 0.05% of applied ¹⁴C in celery, carrot and pak choi, respectively. The bioconcentration factors (BCFs) based on ¹⁴C measurements ranged from 7.6 to 26.1 for celery, 3.6–12.9 for carrot, and 4.4–44 for pak choi. ¹⁴C-CBZ was easily translocated from the roots to the leaves and/or stems. The amendment of biosolids had a significant inhibitory effect on the uptake and translocation of ¹⁴C-CBZ from soil.