Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in the sediments of Daihai Lake in Inner Mongolia, China

Lake shrinkage-induced terrestrial ecological environmental quality degradation in a semiarid lake basin

Lake water environmental problems caused by lake shrinkage in semiarid zones have attracted widespread attention, but few studies have quantified the impact of lake shrinkage on the terrestrial ecological environmental quality of watersheds. In this study, remote sensing image inversion, digital elevation modeling, and statistical analysis were applied to explore the impact of Lake Daihai shrinkage on the terrestrial ecological environmental quality of its receding water areas from 1986 to 2019. The results showed that the area of Lake Daihai shrank from 170.7 km2 in 1961 to 50.67 km2 in 2019, a shrinkage of 70.32%. The average annual shrinkage was 2.07 km2 during the period of 1986-2019 (r = -0.99, p < 0.01). The main conclusions of this study are as follows: The mean remote sensing ecological index values decreased significantly from 0.628 in 1986 to 0.441 in 2019 (r = -0.78, p < 0.05), which means that the terrestrial ecological environmental quality of the water receding area degraded from a good grade to a moderate grade. The increase in water use by residents in the basin was an important reason for the shrinkage of Lake Dahai. Approximately 90% of the wetlands in the receding water areas formed after the shrinkage of Lake Daihai were converted to farmland by local residents, which significantly degraded the terrestrial ecological environmental quality of these areas from good to moderate grade over the 34-year period (r = -0.83, p < 0.05). Correlation analysis indicated that the remote sensing ecological index was positively correlated with lake area (r = 0.85, p < 0.01). The results indicate that steps should be taken to decrease the impact of human activities on the terrestrial ecological environmental quality of lake basins in semiarid zones.

Distribution, sources, and health risk of polycyclic aromatic hydrocarbons and their derivatives in the watershed: the case of Yitong River, China

Polycyclic aromatic hydrocarbons (PAHs) and substituted PAHs (SPAHs) are persistent organic pollutants prevalent globally, and SPAHs have received widespread attention in recent years due to their stronger toxicity and carcinogenicity compared to PAHs. There is a lack of systematic examination of PAHs and their derivatives in watersheds. Thus, to clarify the current status, possible sources, and potential risks of PAHs and their derivatives in watersheds, a study was conducted on Yitong River in China. The results showed that the concentrations of ∑PAHs, ∑OPAHs, and ∑NPAHs ranged from 297.9-1158.3 ng/L, 281.1-587.2 ng/L, and 65.7-269.1 ng/L, respectively. Diagnostic ratio analysis showed that the PAHs were mainly derived from petroleum sources, agricultural waste, and coal combustion. Nitrated PAHs (NPAHs) were mainly derived from liquid combustion sources, and oxygenated PAHs (OPAHs) were derived mainly from petroleum source emissions and atmospheric deposition. The exposure risk model of PAHs revealed that 86% of the studied sites would pose carcinogenic risks after dermal contact. The contaminant causing a major carcinogenic risk was DahA, and none of the sites produced non-carcinogenic risks. The lifetime carcinogenic risk of NPAHs was 8.85 × 10^-10-1.44 × 10^-4, and some surface waters presented with potential carcinogenic risks.

Historical evolution of polycyclic aromatic hydrocarbon pollution in Chaihe Reservoir from 1863 to 2018

Pollution from polycyclic aromatic hydrocarbons (PAHs) spreads and changes worldwide. The pollution evolution in the regional water environment evolves in response to multiple factors, requiring considerable attention. PAH heterogeneity in the sediment core from Chaihe Reservoir was investigated to indicate dynamic changes in PAH pollution levels and sources and propose recommendations for controlling PAHs. Dynamic PAH patterns showed that the overall decline in PAH pollution was in association with local anthropogenic activities, temperature, and precipitation over the period 1863-2018. Nevertheless, coal, oil, and natural gas consumptions still played significant roles in transferring PAHs to the reservoir. Meanwhile, there were dominant local origins, including grass, wood, and coal combustion. The results highlight that the joint action of natural and anthropogenic interventions mitigated PAH pollution in the reservoir. Promoting improved fuels, new energy vehicles, and cleaner energy may further lower PAH pollution.

Assessment of seasonal variation in distribution, source identification, and risk of polycyclic aromatic hydrocarbon (PAH)-contaminated sediment of Ikpoba River, South-South Nigeria

The study aims to assess the seasonal variation in distribution, source identification, and risk of 20 polycyclic aromatic hydrocarbons (20 PAHs) in the sediment of the Ikpoba River, south-south Nigeria. The PAHs were extracted in an ultrasonic bath with a mixture of n-hexane and dichloromethane (1:1 v/v). The extract was cleaned by silica-alumina gel mixed with anhydrous Na₂SO₄ in a chromatography column, eluted by n-hexane, and analysed by gas chromatography-mass spectrometry. The range of the average PAHs in mg.kg-dw was 0.15 (Nap)-0.54 (Acy) and 0.13 (D.al.P)-0.99 (Acy) in wet and dry periods correspondingly, indicating an increase in concentration from wet to dry period. However, the rings of the average concentration of the PAHs show 6 and 3 rings to be the highest values during the wet and dry seasons, respectively. Based on the human health risk analysis, the hazard quotient (HQ) and hazard index (HI), and carcinogenic risk indices showed low non-carcinogenic and carcinogenic risk for both seasons. The ecological risk analysis showed the mean effect range median quotient (mERMQ) recorded a medium-low effect on the biota of the locations, except in AS3 during the wet season and also in WS8 and WS9 during the dry season. The minimum value of the toxic equivalent quotient (TEQ) was > 0.2 mg/kg, which indicated a recommendation for the clean-up of the Ikpoba River. The isomer ratio and the principal component analysis (PCA) revealed the sources of the PAHs to be majorly combustion, followed by pyrolytic and petrogenic sources for both seasons.

Polycyclic aromatic hydrocarbons in remote lakes from the Tibetan Plateau: Concentrations, source, ecological risk, and influencing factors

Polycyclic aromatic hydrocarbons (PAHs) have received worldwide attention due to their potential teratogenic, persistent, and carcinogenic characteristics. In this study, the PAHs concentrations in two dated sediment cores taken from central Tibetan Plateau (TP) were analyzed to study the deposition history, potential sources, ecological risks, and influencing factors. Total concentration of PAHs (∑PAHs) ranged from 50.0 to 195 ng g^-1 and 51.9-133 ng g^-1 in sediments of Pung Co (PC) and Dagze Co (DZC), respectively. 2-3-ring PAHs were dominant in the two lake sediments, accounting for an average of 77.5% and 80.1%, respectively. The historical trends of ∑PAHs in the two lakes allowed to distinguish three periods, namely, relative stability before the 1950s, a gradual increase between the 1950s and the 1990s, and then a decline to the present-day. In addition, the trend in the concentration level of each PAH composition was consistent with ∑PAHs before the 1990s, while they exhibited different trends since the 1990s, which may be the result of a combination of anthropogenic activities and climate change in recent years, whereas before the 1990s the PAH profile was mainly influenced by atmospheric deposition. The results of source apportionment examined according to diagnostic ratios and positive matrix factorization were consistent and revealed that PAHs were primarily derived from biomass and coal combustion. Significant correlations between PAHs and organic carbon (OC) indicate that OC might be a key factor influencing the concentration of PAHs in sediments. The ecological risk assessment demonstrated that PAHs in TP sediments occurred at a low risk level. Results of this study could be helpful to develop a deeper insight into the deposition history of PAHs in remote lakes of the TP region and explore the response of these variations to climate change and human activities.

Metagenomic analysis of microbial community structure and distribution of resistance genes in Daihai Lake, China

The emergence of resistance genes is a global phenomenon that poses a significant threat to both animals and humans. Lakes are important reservoirs of genes that confer resistant to antibiotics and metals. In this study, we investigated the distribution and diversity of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in the sediment of Daihai Lake using high-throughput sequencing and metagenomic analysis. The results indicated that all sampling sites had similar bacterial community structures, with Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes being the most abundant. A total of 16 ARG types containing 111 ARG subtypes were deposited in the sediment. Among the resistance genes to bacitracin, multidrug, macrolide-lincosamide-streptogramin (MLS), tetracycline, beta-lactam, and sulfonamide were the dominant ARG types, accounting for 89.9-94.3% of the total ARGs. Additionally, 15 MRG types consisting of 146 MRG subtypes were identified. In all samples, MRGs of the same type presented resistance to Pb, Ni, Hg, W, Zn, Ag, Cr, Fe, As, Cu, and multimetals. Overall, the distribution and diversity of antibiotic and metal resistance genes showed no significant differences in the samples. Plasmids (91.03-91.82%) were the most dominant mobile genetic elements in the sediments of Daihai Lake. Network analysis indicated that the target ARGs and MRGs were significantly positively correlated with the microorganisms. Potential hosts for various ARGs and MRGs include Proteobacteria, Euryarchaeota, Actinobacteria, Chloroflexi, and Bacteroidetes.

Spatial-temporal distributions and influential factors of phthalate acid esters in sediments of three lakes in Inner Mongolia

The spatiotemporal distributions, influential factors, and ecological risks of 15 phthalate acid esters (PAEs) in the sediments of three typical lakes in Inner Mongolia were investigated in this work. PAEs were widespread in all surface sediments ranging from 598.3 to 3873.8 μg/kg dry weight. Average PAE concentrations were highest in the surface sediments of Wuliangsuhai Lake followed by Daihai and Hulun Lakes, which were consistent with population density and intensity of anthropogenic activities. Dibutyl phthalate, di-iso-butyl phthalate (DIBP), and diethyl phthalate (DEP) were the dominant PAEs with similar abundance orders for the three lakes. The cold climate could explain the higher DEP abundance in the sediments of lakes at higher latitudes. The highest Σ PAE and most individual PAE concentrations were located at one of the discharge river estuaries because most PAEs were terrestrial pollutants. Σ PAE concentrations in the core sediments increased with years and fluctuations owing to the increasing PAE usage and input. The second highest PAE concentration peaks were associated with the high gross domestic product growth rates in 2003-2008. Redundancy analysis revealed that butyl benzyl phthalate and diamyl phthalate in the surface sediments of Hulun Lake were principally positively influenced by organic matter (65.6% contribution among geochemical variables), Fe oxides (25.1% contribution among metals), and Mn oxides (23.8% contribution among metals). The DIBP and DEP exhibited high risks to sensitive fish according to a risk quotient assessment. This work presents new insights into PAE status and deposition mechanisms in the lakes within high latitudes or cold climates, and provides important information for future environmental protection and management.