Fertilization with organic matter (farm yard manure and/or rice straw) is thought to enhance arsenic (As) mobilization into soil porewaters, with subsequent As assimilation by rice roots leading to enhanced translocation to the grain. Here, interlinked experiments (field manuring and soil batch culture) were conducted to find the effect of organic matter at a field application rate practiced in Bangladesh (5 t/ha) on As mobilization in soil for paddies impacted by As contaminated groundwater irrigation, a widespread phenomenon in Bangladesh where the experiments were conducted. Total As concentration in a paddy soil (Sonargaon) ranged from 21.9 to 8.1 mg/kg down the soil profile and strongly correlated with TOC content. Arsenic, Fe, Mn, and DOC release into soil solution, and As speciation, are intimately linked to OM amendment, soil depth and temporal variation. Organic matter amendments lead to increased mobilization of As into both soil porewaters and standing surface waters. The As speciation in the porewater was dominated by inorganic As (Asᵢ) (arsenite and arsenate), with traces amounts of methylated species (DMAⱽ and MMAⱽ) only being found with OM amendment. It was noted in field trials that OM fertilization greatly enhanced As mobility to surface waters, which may have major implications for the fate of As in paddy agronomic ecosystems.

The Sichuan Basin (SCB) in southwestern China is largely affected by air pollution. Understanding the responses of air pollutant concentrations to emission changes is critical for designing and evaluating effective control strategies. Thus, this study used the Community Multi-scale Air Quality (CMAQ) model to simulate PM₂.₅ (i.e., particulate matter with an aerodynamic diameter ≤ 2.5 μm) in winter (January 2015) and ozone (O₃) in summer (July 2015) under nine emission reduction scenarios. For each scenario, the anthropogenic emissions of each air pollutant in each SCB grid cell were reduced by the same percentage, ranging from 10% to 90%. We found that approximately 30–70% emission reductions are required to reduce the January mean PM₂.₅ concentrations in all the SCB urban centers to a value that is less than the Chinese standard for daily mean PM₂.₅ (24-h PM₂.₅: 75 μg m⁻³). However, the January mean PM₂.₅ concentrations under 90% emission reduction still exceeded the World Health Organization (WHO) guideline (25 μg m⁻³) in 16 SCB urban centers. Moreover, reducing both SCB and non-SCB emissions were critical for achieving the PM₂.₅ level recommended by WHO. An 80% emission reduction was required to prevent the occurrence of 8-h O₃ (i.e., daily maximum 8-h mean O₃) non-attainment days in all SCB urban centers. Under 90% emission reduction, July mean 8-h O₃ concentrations still exceeded the WHO guideline of 47 ppb in approximately 35% of the SCB areas. In conclusion, this study suggests that (1) compared with the governmental emission reduction targets for 2015–2020 (2–27%), more significant emission reductions are required to meet the Chinese and WHO pollution standards; and (2) both SCB and non-SCB emissions must significantly reduce to achieve the desired pollution targets.

Polybrominated diphenyl ethers (PBDEs) are listed as persistent organic pollutants (POPs) in the Stockholm Convention. It has been established that PBDEs may be released into the environment during improper handling and disposal of e-waste and other products containing PBDEs that is prevalent in developing countries. This research work assessed the status of PBDE contamination at dumpsites in Nigeria. Soil and edible plant samples were collected from the dumpsites and control sites for analysis. The concentrations of ∑₇PBDE in the topsoils around the dumpsites at 0–15 cm depth ranged from 112 to 366 ng/g dry weight (dw) while that of the topsoil of the control site 500 m from the dumpsite ranged from 26.8 to 39.7 ng/g dw. These high concentrations stem likely from open burning of waste including electronic waste on the landfills. Plant samples (bentgrass, spinach, tomatoes, pumpkin and sweet potatoes) around the dumpsites were found to be contaminated by PBDEs with levels ranging from 25.0 to 60.5 ng/g dw in plant roots and from 8.45 to 32.2 ng/g dw in plant shoots for ∑₇PBDE. This suggests that consumption of vegetables by humans and ingestion of contaminated soils and feed by chickens and cows can transfer PBDEs into the human food chain around the dumpsites. The comparison of PBDE levels in soils and the PBDE levels in chicken eggs from the former study indicate that PBDE levels in the soils are sufficient to explain the levels in the chicken eggs with a reasonable carry-over rate for PBDEs of 0.28 on average. The PBDE contamination in the soil was sufficient to result in a relevant exposure of humans via accumulation in eggs. The study shows that a better management of end-of-life products containing PBDEs is needed to reduce PBDE exposure risk in Africa.

PM₂.₅-bound PAHs were analyzed in a total of 135 daily samples collected during four seasons from 2018 to 2019, at three urban sites in Tehran, Iran. This study aims to investigate spatio-temporal variations, source apportionment, potential local and regional sources contributions and lung cancer risks associated with the 16 US EPA priority PAHs. PM₂.₅ concentrations ranged from 43.8 to 80.3 μg m⁻³ with the highest concentrations observed in summer. Total PAHs (TPAHs) concentrations ranged between 24.6 and 38.9 ng m⁻³. Autumn period exhibited the highest average concentration (48.3 ng m⁻³) followed by winter (29.5 ng m⁻³), spring (25.9 ng m⁻³) and summer (16.1 ng m⁻³). Five PAHs sources were identified by positive matrix factorization (PMF) analysis: diesel exhaust, unburned petroleum-petrogenic, industrial, gasoline exhaust and coal/biomass combustion-natural gas emissions, accounting for 22.3%, 15.6%, 7.5%, 30.9%, and 23.6% of TPAHs, respectively. Site-specific bivariate polar (BP) and conditional bivariate probability function (CBPF) plots were computed to assess PM₂.₅ and TPAHs local source locations. CBPF pointed out that TPHAs sources are likely of local origin, showing the highest probability close to the sampling sites associated with low wind speed (<5 m s⁻¹). The potential source contribution function (PSCF) and the concentration weighted trajectory (CWT) models were applied to investigate the long-range transport of PM₂.₅ and TPAHs. In addition to local sources contributions, Eastern areas were highly related to long-distance transport of PM₂.₅ and the Western areas showed the highest contribution of the total, medium molecular weight (MMW) (4 rings) and high molecular weight (HMW) (5–6 rings) PAHs. The upper bound of incremental lifetime cancer risk (ILCR) via inhalation exposure to PM₂.₅-bound PAHs was at a moderate risk level (3.14 × 10⁻⁴ to 6.17 × 10⁻⁴).

Urine sample tests are one of the most common methods of estimating human exposure to polycyclic aromatic hydrocarbons (PAHs) and assessing population health risks. To evaluate the reliability of the urine test and the impact of other PAH elimination routes on the health risk estimated by this test, we proposed a backward modeling framework integrating other common elimination routes of PAH metabolites to calculate the overall intake rate of the parent PAH based on the levels of corresponding main metabolites in urine. Due to limited biotransformation data, we selected naphthalene as an example to evaluate model performance and collected urine samples from 234 random adults in Shenzhen. The overall intake rates of naphthalene were then simulated and compared to current literature data. The simulated intake rates of naphthalene ranged from 3.70 × 10⁻³ mg d⁻¹ to 1.95 mg d⁻¹ and followed a lognormal distribution with a median value of 6.51 × 10⁻² mg d⁻¹. The results indicated that, if naphthalene exposure occurred only via food for the population of Shenzhen, the literature data fell within the most frequent interval [3.70 × 10⁻³, 4.45 × 10⁻²] but were lower than the simulated median value. However, if other exposure routes were considered, the allocation factor-adjusted literature data were close to the simulated median values. In addition, under normal physiological conditions, the simulated results were more sensitive to 1-hydroxynaphthalene (1-OHN) and 2-hydroxynaphthalene (2-OHN) levels in urine than other biometric variables, which is due to the limited load of 1-OHN and 2-OHN in human elimination routes. Furthermore, the suggested safety levels of 1-OHN and 2-OHN in urine to protect 99% of the general population of Shenzhen were 6.40 × 10⁻⁶ and 3.75 × 10⁻⁵ mg L⁻¹, which could be used as regulatory indicators based on the high reliability of the model.

Outdoor concentrations of particulate matter with an aerodynamic diameter of <2.5 μm (PM₂.₅) are often used as a surrogate for population exposure to PM₂.₅ in epidemiological studies. However, people spend most of their daily activities indoors; therefore, the relationship between indoor and outdoor PM₂.₅ concentrations should be considered in the estimation of population exposure to PM₂.₅. In this study, a population exposure model was developed to predict seasonal population exposure to PM₂.₅ in Seoul, Korea. The input data for the population exposure model comprised 3984 time-location patterns, outdoor PM₂.₅ concentrations, and the microenvironment-to-outdoor PM₂.₅ concentrations in seven microenvironments. A probabilistic approach was used to develop the Korea simulation exposure model. The determinants for the population exposure group were identified using a multinomial logistic regression analysis. Population exposure to PM₂.₅ varied significantly among the three seasons (p < 0.01). The mean ± standard deviation of population exposures to PM₂.₅ was 21.3 ± 4.0 μg/m³ in summer, 9.8 ± 2.7 μg/m³ in autumn, and 29.9 ± 10.6 μg/m³ in winter. Exposure to PM₂.₅ higher than 35 μg/m³ mainly occurred in winter. Gender, age, working hours, and health condition were identified as significant determinants in the exposure groups. An “unhealthy” health condition was the most significant determinant. The high PM₂.₅ exposure group was characterized as a higher proportion of males of a lower age with longer working hours. The population exposure model for PM₂.₅ could be used to implement effective interventions and evaluate the effectiveness of control policies to reduce exposure.

In the environment, microalgae are exposed to a multitude of stressors simultaneously, inducing physiological adjustments. It is well documented that both phosphorus (P) limitation and trace metals exposure affect microalgal physiology. However, investigations regarding the combination of both P limitation and excess trace metals still deserve attention. In the present study, we evaluated the changes in photosynthetic parameters in the green microalga Ankistrodesmus densus acclimated to different P concentrations prior to exposure to Cd. Our results indicate that different concentrations of P in the medium were responsible for significant changes in some parameters, especially those related to photoprotection mechanisms. Cadmium also altered some of these variables in all P scenarios, and greater damage (i.e., synergism) was observed in the combination P-limited and high Cd, with all the evaluated parameters affected under the adverse scenario. Among the parameters analyzed, rapid light curves were the most sensitive to exposure of one or the combination of both stressors (Cd and P limitation). Based on our data, we suggest that P-limited algae activated photoprotective mechanisms as a response to nutrient limitation, especially at the most limited condition. The addition of Cd did not change linearly the parameters related to photoprotection mechanisms under P-limitation, i.e., synergism was observed in the intermediate P-limitation combined with Cd, while in the most P-limited, P seems to be the driving force affecting these mechanisms. Based on our results, we suggest the use of rapid light curves as a tool to complement the assessment of the impacts of stressors, such as metals, in ecotoxicological studies.

Aquaculture activities in southern Chile demand floating devices to produce electricity powered by diesel generators. It has been recently proposed to replace this fuel with propane. However, little is known about the behaviour and possible environmental impacts of an accidental release of propane underwater. In this study we evaluated the impact of water temperature and salinity on the saturation and further release of propane under controlled laboratory experiments. Results showed that under extreme environmentally relevant scenarios (high and low temperature and salinity), propane saturated the water more quickly. However, while it is important to consider that saturation times can be similar (∼2 h), the magnitudes of propane dissolved can be different. Experiments showed that cold waters (5 °C) propane is dissolved twice than warm waters (20 °C). Residence time was more affected by water temperature and almost independent of water salinity. Propane may take at least 2 days to be released from waters (around 90% of the initial amount dissolved under laboratory conditions).Additionally, we evaluated the impact on dissolved oxygen displacement and the embryotoxicity of the dissolved fraction by using Zebrafish Embryo Toxicity Assay. Results showed that dissolved oxygen was quickly removed. However, the levels of dissolved oxygen were promptly recovered in the studied systems. We also observed that propane can generate genotoxic effects (3–10% mortality), but after 2 days the system can be almost free of propane and the effects may become much lower. Comparatively with the literature, propane showed to be less toxic than diesel and it is a viable and less environmentally hazardous replacement for diesel.

Both submerged macrophytes (SMs) and artificial macrophytes (AMs) have been widely used to improve water quality in eutrophic water. However, in heavily eutrophic aquatic ecosystems, the purification function of SMs is often restricted by the poor growth state due to competition from algae, while the purification function of AMs is often restricted by the limited carbon source supply for biofilm microbes attached to the AM surface. The objective of this study was to develop a new strategy to increase pollutant removal efficiency (RE) by combining the use of SMs and AMs. Pilot-scale microcosms, including treatments with both SMs and AMs (S&A), only SMs (SO) and only AMs (AO), were established to identify the performance of the new strategy. The results suggest that treatment S&A obtained REs of 88.9% for total nitrogen (TN) and 48.1% for chemical oxygen demand (COD); as comparison, treatments SO and AO obtained REs of 77.4% and 81.2% for TN and REs of −13.7% and 39.0% for COD, respectively. Compared with SO, the S&A treatment benefited SM growth in biomass, leaf chlorophyll concentration and root activity by inhibiting algae growth. In addition, compared with treatment AO, S&A increased the biofilm microbial biomass and the relative abundance of nitrifiers of families Nitrosomonadaceae and Nitrospira attached to AM surfaces. Therefore, by the mutual promotion of SMs and biofilms on AMs, the synergic application of SMs and AMs is a useful strategy for improving TN and COD REs in eutrophic water bodies such as rivers and constructed wetlands.A strategy was developed to increase nitrogen and COD removal in eutrophic water by the mutual promotion of submerged macrophytes and biofilms on artificial macrophytes.

The concentrations of PBDEs, NBFRs, DP, PCBs, and OCPs were analyzed in water samples of the Yellow River Basin (YRB) and in soil and maize samples collected from basin irrigation areas to understand the status of POPs and associated health risks. The results showed: (1) the congeners of eight PBDEs and seven NBFRs were detected in 10 tributaries, with average concentrations of 1575 and 4288 pg. L⁻¹. Thirty-three congeners of PCBs were detected, and the average concentration of PCB was 232 pg. L⁻¹. Five HCHs were the primary congeners among twenty-three congeners of OCPs in the ten tributaries, accounting for 79% of the total. The average concentration of OCPs was 8287 pg. L⁻¹. (2) Similar congeners of HFRs, PCBs, and OCPs were found in the trunk water. The ranking based on the HFR concentration was upstream > downstream > midstream, and that of the PCB and OCP concentration was downstream > upstream > midstream. (3) PCBs and OCPs in the trunk water of the YRB and in the soil and maize irrigated with river water pose potential carcinogenic and non-carcinogenic risks. The results indicate considerable organic pollution in the YRB, suggesting that national emission standards for POPs should be implemented soon.