Substituted polycyclic aromatic hydrocarbons (sub-PAHs) are receiving increased attention due to their high toxicity and ubiquitous presence. However, the accumulation behaviors of sub-PAHs in crop roots remain unclear. In this study, the accumulation mechanism of sub-PAHs in crop roots was systematically disclosed by hydroponic experiments from the perspectives of utilization, uptake, and elimination. The obtained results showed an interesting phenomenon that despite not having the strongest hydrophobicity among the five sub-PAHs, nitro-PAHs (including 9-nitroanthracene and 1-nitropyrene) displayed the strongest accumulation potential in the roots of legume plants, including mung bean and soybean. The nitrogen-deficient experiments, inhibitor experiments, and transcriptomics analysis reveal that nitro-PAHs could be utilized by legumes as a nitrogen source, thus being significantly absorbed by active transport, which relies on amino acid transporters driven by H+-ATPase. Molecular docking simulation further demonstrates that the nitro group is a significant determinant of interaction with an amino acid transporter. Moreover, the depuration experiments indicate that the nitro-PAHs may enter the root cells, further slowing their elimination rates and enhancing the accumulation potential in legume roots. Our results shed light on a previously unappreciated mechanism for root accumulation of sub-PAHs, which may affect their biogeochemical processes in soils.

To understand the pollution status and risk levels in the Laizhou Bay, the spatiotemporal distribution, source, and ecological risk of 16 polycyclic aromatic hydrocarbons (PAHs) and 20 substituted PAHs (SPAHs) were studied in surface sediments in 2022. The findings indicated significant seasonal differences in the concentrations of PAHs and SPAHs under the influences of precipitation, temperature, light, and human activities, with higher storage levels in summer than in spring, and there was also a spatial distribution trend of estuary > coast > offshore. 2-Nitrofluorene (2-NF) and 2-methylnaphthalene (2-MN) were the most abundant components of SPAHs in both spring and summer, with levels of 21.44 ng/g and 17.89 ng/g in spring, 43.22 ng/g and 25.51 ng/g in summer, respectively. The results of the diagnostic ratio and principal component analysis - multiple linear regression identified sources of PAHs and SPAHs as combustion sources, including petroleum, coal, and biomass. The risk level of PAHs was low-to-moderate according to the toxicity equivalent quotient (TEQ) and risk quotient. A novel calculation method based on TEQ was proposed to assess the ecological risk of SPAHs, and the results indicated that the risk level of SPAHs was moderate-to-high.

Substituted polycyclic aromatic hydrocarbons (SPAHs) are a type of emerging pollutant that widely exist in the environment, which also exhibit carcinogenicity, mutagenicity, and teratogenicity. These pollutants belong to toxic pollutants because of their similar structures to polycyclic aromatic hydrocarbons (PAHs). Their environmental behavior and ecological risk have attracted increasing attention. Based on a literature review, we found a new breakthrough in the source, distribution, behavior, and risk of SPAHs with comparison to traditional pollutants PAHs. This paper reviewed the current research progress on the environmental occurrence and photochemical behavior of SPAHs. Their sources, formation mechanisms, and distribution characteristics in the multimedia environment were highlighted, and the photochemical transformation kinetics, pathways, and affecting factors of SPAHs in water, ice, and other media were discussed. Furthermore, the research prospects about the environmental behavior and risk of SPAHs were proposed.

In this study, a novel wastewater treatment process combining sequencing batch reactor, constructed wetland and microalgal membrane photobioreactor (BCM process) was proposed, and its performance on removal, transformation and toxicity reduction of polycyclic aromatic hydrocarbons (PAHs) was intensively explored. Satisfactory PAHs removal (90.58%-97.50%) was achieved and molecular weight had significant impact on the removal pathways of different PAHs. Adsorption dominated the removal of high molecular weight PAHs, while the contribution ratio of microbial degradation increased with the decrease of molecular weight of PAHs. More importantly, it was reported for the first time that substituted PAHs (SPAHs) produced by microbial degradation of PAHs would lead to increased toxicity during the BCM process. High PAHs (75.37%-88.52%) and SPAHs removal (99.56%-100.00%) were achieved in the microalgae unit due to its abundant cytochrome P450 enzyme, which decreased the bacterial toxicity by 90.93% and genotoxicity by 93.08%, indicating that microalgae played significance important role in ensuring water security. In addition, the high quantitative relationship (R2 = 0.98) between PAHs, SPAHs and toxicity exhibited by regression model analysis proved that more attention should be paid to the ecotoxicity of derivatives of refractory organic matters in wastewater treatment plants.

This paper reports for the first time the occurrence, fates, and carcinogenic risks of 20 substituted polycyclic aromatic hydrocarbons (SPAHs) and 16 priority PAH species in two coking wastewater treatment plants (WWTPs) (plant E and central WWTP). The measured total concentrations of PAHs and SPAHs in raw wastewater of coking plant E were 3700 and 1200 μg·L-1, respectively, with naphthalene (1400 μg·L-1), and fluoranthene (353 μg·L-1) as dominant PAH species and 2-methylnaphthalene (167 μg·L-1), anthraquinone (133 μg·L-1), and 1-methylnaphthalene (132 μg·L-1) as dominant SPAHs. For the 11 methyl-PAHs (MPAHs), 4 oxygenated-PAHs (OPAHs), and 5 nitrated-PAHs (NPAHs) investigated, the biological wastewater treatment process removed 98.6% MPAHs, 83.9% OPAHs, and 89.1% NPAHs. Mass balance analysis result revealed that transformation was the major mechanism to remove low-molecular-weight (LMW) MPAHs (59.9-77.3%), a large part of OPAHs, including anthraquinone, methylanthraquinone, and 9-fluorenone (46.7-49.6%), and some NPAHs, including 2-nitrofluorene and 9-nitroanthrancene (52.9-59.1%). Adsorption by activated sludge mainly accounted for removing high-molecular-weight (HMW) SPAHs (59.6-71.01%). The relatively high concentrations of SPAHs in excess sludge (15,000 μg·g-1) and treated effluent (104 μg·L-1) are of great concern for their potential adverse ecological impacts. SPAHS exhibited similar behaviors in central WWTP, though the influent concentrations were much lower. The concentration levels of SPAHs in the ambient air of coking plant E and central WWTP may also pose potential lung cancer risks (LCR) to the workers through inhalation, where all studied SPAHs except 3-nitrofluoranthene and 7-nitrobenz[a]anthracene exceeded the acceptable cancer risk standards (>10-6) recommended by U.S EPA. This study could help identify the ecological and healthy risks during coking wastewater treatment and provide useful information for policy-making.

Like their parent polycyclic aromatic hydrocarbons (PAHs), substituted polycyclic aromatic hydrocarbons (SPAHs), including methyl PAHs (MPAHs), oxygenated PAHs (OPAHs), and chlorinated PAHs (ClPAHs), exist ubiquitously in urban and agricultural rivers. Although laboratory studies have found the biological toxicities of certain SPAHs to be higher than that of their parent PAHs, the ecological risk of SPAHs in rivers has been largely ignored. Here, we studied the distribution, source and transport of PAHs and SPAHs as well as ecological risks in the Chaobai River System, which experiences a high level of anthropogenic activity. The results show that the concentration of ΣOPAHs (321 ± 651 ng/L) was higher than that of ΣPAHs (158 ± 105 ng/L), ΣMPAHs (28 ± 22 ng/L), and ΣClPAHs (30 ± 12 ng/L). We also found that (S)PAHs in Chaobai River mainly originated from Beiyun River (53%-65%), which receives considerable municipal wastewater treatment plant effluent from Beijing. The major transport pathway of (S)PAHs from Chaobai River was likely for irrigation (83%-86%) and transportation into Yongdingxin River (13%-16%), which finally merged into the Bohai Sea. The mixed chronic risk of (S)PAHs (risk quotient = 45 ± 53) was higher than the mixed acute risk (risk quotient = 1.9 ± 1.4), with all sites facing chronic risk and 90% of sites experiencing acute risk. Although the chronic and acute risks of (S)PAHs to plants, invertebrates, and vertebrates were mainly from PAHs (97.5% to chronic risk and 96.5% to acute), SPAHs still posed a chronic risk to invertebrates and vertebrates (risk quotient > 1). Accordingly, the ecological risk of (S)PAHs in Chaobai River should be taken into consideration for ecosystem protection. The transmission of PAHs and SPAHs from Chaobai River may also pose potential risks to farmland through irrigation, as well as to the Bohai Sea via river water discharge.

Sixteen polycyclic aromatic hydrocarbons (PAHs) and some typical substituted polycyclic aromatic hydrocarbons (SPAHs) were investigated in wastewater treatment plants (WWTPs) and effluent effluent-receiving rivers in order to indentify the elimination of these compounds in WWTPs, as well as the potantial potential risk in the effluent-receiving rivers. The concentrations of ΣPAHs in the total phase (combined dissolved and adsorbed phases) in influent were between 944.1 and 1246.5 ng·L-1, and ΣSPAHs, including methyl PAHs (MPAHs) and oxygenated PAHs (OPAHs), between 684.9 and 844.9 ng·L-1. Regarding the SPAHs, the concentrations of ΣOPAHs (312.3 ng·L-1) were higher than those of ΣMPAHs (271.8 ng·L-1). The total removal efficiencies of PAHs in the biological treatment processes were between 59% and 68%, and those of SPAHs were a little lower (58-65%). The removal efficiency in the adsorbed phase was higher than in the dissolved phase. The concentrations of PAHs and SPAHs in the effluent were a little higher than in the receiving river. According to a PAH risk assessment of the effluent, 7 carcinogenic PAHs accounted for a relatively high proportion. Benzo[a]pyrene (BaP) and Dibenz[a,h]anthracene (DBA) were major contributors to the TEQs in the effluent of WWTPs, which should be taken into consideration.

Substituted polycyclic aromatic hydrocarbons (SPAHs) occur ubiquitously in the whole global environment as a result of their persistence and widely-spread sources. Some SPAHs show higher toxicities and levels than the corresponding PAHs. Three types of most frequently existing SPAHs, oxygenated-PAHs (OPAHs), nitrated-PAHs (NPAHs), and methyl-PAHs (MPAHs), as well as the 16 priority PAHs were investigated in this study. The purpose was to identify the occurrence, possible transformation, and source and fate of these target compounds in a water shortage area of North China. We took a river system in the water-shortage area in China, the Haihe River System (HRS), as a typical case. The rivers are used for irrigating the farmland in the North of China, which probably introduce these pollutants to the farmland of this area. The MPAHs (0.02-0.40 μg/L in dissolved phase; 0.32-16.54 μg/g in particulate phase), OPAHs (0.06-0.19 μg/L; 0.41-17.98 μg/g), and PAHs (0.16-1.20 μg/L; 1.56-79.38 μg/g) were found in the water samples, but no NPAHs were detected. The concentrations of OPAHs were higher than that of the corresponding PAHs. Seasonal comparison results indicated that the OPAHs, such as anthraquinone and 2-methylanthraquinone, were possibly transformed from the PAHs, particularly at higher temperature. Wastewater treatment plant (WWTP) effluent was deemed to be the major source for the MPAHs (contributing 62.3% and 87.6% to the receiving river in the two seasons), PAHs (68.5% and 89.4%), and especially OPAHs (80.3% and 93.2%) in the rivers. Additionally, the majority of MPAHs (12.4 kg, 80.0% of the total input), OPAHs (16.2 kg, 83.5%), and PAHs (65.9 kg, 93.3%) in the studied months entered the farmland through irrigation.

Wastewater treatment plant (WWTP) effluent is the major source for substituted polycyclic aromatic hydrocarbons (SPAHs) to the receiving rivers, as well as the parent PAHs. Some of the SPAHs showed higher toxicities and levels than their parent PAHs. The occurrence and behavior of typical SPAHs were investigated in a representative biological WWTP in Beijing, China. Methyl PAHs (MPAHs) (149-221 ng/L in the influent; 29.6-56.3 ng/L in the effluent; 202-375 ng/g in the activated sludge), oxygenated PAHs (OPAHs) (139-155 ng/L; 69.9-109 ng/L; 695-1533 ng/g) and PAHs (372-749 ng/L; 182-241 ng/L; 2402-3321 ng/g) existed, but nitrated PAHs (NPAHs) were not detected. 2-Methylnaphthalene, anthraquinone, 9-fluorenone and 2-methylanthraquinone were the predominant SPAHs. OPAHs were deduced to be formed from PAHs especially during summer, based on the ratios variation and removal efficiencies of the two seasons, and the surplus mass in the outflows. Low molecular weight compounds (2-3 rings) might be mainly removed by mineralization/transformation and adsorption in the anaerobic unit, and by volatilization in the aerobic unit. High molecular weight compounds (4-6 rings) might be mainly removed by adsorption in the anaerobic unit. The total outflows of SPAHs and PAHs were 66 g/d in summer and 148 g/d in winter from the WWTP to the receiving river. The percentage of OPAHs was higher in summer than in winter.