Systematic Evaluation of Two Classical Receptor Models in Source Apportionment of Soil Heavy Metal(loid) Pollution Using Synthetic and Real-World Datasets

Due to the lack of a priori knowledge on true source makeup and contributions, whether the source apportionment results of Unmix and positive matrix factorization (PMF) are accurate cannot be easily assessed, despite the availability of built-in indicators for their goodness of fit and robustness. This study systematically evaluated, for the first time, the applicability and reliability of these models in source apportionment of soil heavy metal(loid)s with synthetic datasets generated using known source profiles and contributions and a real-world dataset as well. For eight synthetic datasets with different pollution source characteristics, feasible Unmix solutions were close to the true source component compositions (R2 > 0.936; total mean squared errors (MSEs) < 0.04), while those of PMF had significant deviations (R2 of 0.484–0.998; total MSEs of 0.04–0.16). Nonetheless, both models failed to accurately apportion the sources with collinearity or non-normal distribution. Unmix generally outperformed PMF, and its solutions showed much less dependence on sample size than those of PMF. While the built-in indicators provided little hint on the reliability of both models for the real-world dataset, their sample-size dependence indicated that Unmix probably yielded more accurate solutions. These insights could help avoid the potential misuse of Unmix and PMF in source apportionment of soil heavy metal(loid) pollution

Public Health Risk of Arsenic Species in Chicken Tissues from Live Poultry Markets of Guangdong Province, China

Arsenic-based feed additives, such as roxarsone (ROX), are still legally and widely used in food animal production in many countries. This study was conducted to systematically characterize the content and speciation of arsenic in chicken tissues from live poultry markets and in commercial chicken feeds in Guangdong, a major poultry production and consumption province in China, and to assess the corresponding public health risk. The total arsenic contents in the commercial feeds could be modeled as a mixture of two log-normal distributions (geometric means: 0.66 and 17.5 mg/kg), and inorganic arsenic occurred at high levels (0.19–9.7 mg/kg) in those with ROX detected. In general, chicken livers had much higher contents of total arsenic compared to the muscle tissues (breast and drumstick), and chicken muscle from the urban markets contained arsenic at much higher levels than that from the rural markets. The incremental lifetime cancer risk (bladder and lung cancer) from dietary exposure to arsenic contained in chicken meat products on local markets was above the serious or priority level (10^–4) for 70% and 30% of the adult populations in Guangzhou and Lianzhou, respectively. These findings indicate the significant need to phase out the use of arsenic-based feed additives in China

Bioaccessibility of PAHs in Fuel Soot Assessed by an in Vitro Digestive Model with Absorptive Sink: Effect of Food Ingestion

We investigated the effects of changing physiological conditions in the digestive tract expected with food ingestion on the apparent bioaccessibility (<i>B</i>_app) of 11 polycyclic aromatic hydrocarbons (PAHs) in a fuel soot. A previously established in vitro digestive model was applied that included silicone sheet as a third-phase absorptive sink simulating passive transfer of PAHs to intestinal epithelium in the small intestine stage. The <i>B</i>_app is defined as the fraction found in the digestive fluid plus sheet after digestion. We determined that <i>B</i>_app was independent of gastric pH and addition of nonlipid milk representing dietary proteins and carbohydrates, whereas it increased with bile acids concentration (2.0–10 g/L), small intestinal pH (5.00–7.35), and addition of soybean oil representing dietary lipid (100% and 200% of the mean daily ingestion by 2–5 year olds in the U.S.). <i>B</i>_app of PAHs increases with small intestinal pH due to the combined effects of mass transfer promotion from nonlabile to labile sorbed states in the soot, weaker sorption of the labile state, and increasingly favorable partitioning from the digestive fluid to the silicone sink. Under fed conditions, <i>B</i>_app increases with inclusion of lipids due to the combined effects of mass transfer promotion from nonlabile to labile states, and increasingly favorable partitioning into bile acid micelles. Our results indicate significant variability in soot PAH bioaccessibility within the range of physiological conditions experienced by humans, and suggest that bioaccessibility will increase with coconsumption of food, especially food with high fat content

Bioacessibility of PAHs in Fuel Soot Assessed by an <i>in Vitro</i> Digestive Model: Effect of Including an Absorptive Sink

Polycyclic aromatic hydrocarbons (PAHs) associated with soot or black carbon can enter the human digestive tract by unintentional ingestion of soil or other particles. This study investigated the bioaccessibility of 11 PAHs in a composite fuel soot sample using an <i>in vitro</i> digestive model that included silicone sheet as an absorptive sink during the small intestinal digestion stage. The sheet was meant to simulate the passive transfer of PAHs in lumen fluid across the small intestinal epithelium, which was postulated to promote desorption of labile PAHs from the soot by steepening the soot–fluid concentration gradient. We show that the presence of silicone sheet during a 4 h default digestion time significantly increased the apparent bioaccessible fraction (<i>B</i>_app, %), defined as the sum in the sheet and digestive fluid relative to the total PAH determined. The ability to increase <i>B</i>_app for most PAHs leveled off above a sheet-to-soot ratio of 2.0 g per 50 mg, indicating that the sheet is an effective absorptive sink and promotes desorption in the mentioned way. Enhancement of <i>B</i>_app by the sheet correlated positively with the octanol–water partition coefficient (<i>K</i>_ow), even though the partition coefficient of PAH between sheet and digestive fluid (which contains bile acid micelles) correlated negatively with <i>K</i>_ow. It was hypothesized that PAHs initially in the soot exist in labile and nonlabile states. The fraction of labile PAH still sorbed to the soot residue after digestion, and the maximum possible (limiting) bioaccessibility (<i>B</i>_lim) could be estimated by varying the sheet-to-soot ratio. We show conclusively that the increase in bioccessibility due to the presence of the sheet is accounted for by a corresponding decrease in fraction of labile PAH still sorbed to the soot. The <i>B</i>_lim ranged from 30.8 to 62.4%, independent of molecular size. The nonlabile fraction of individual PAHs (69.2–37.6% in this case) is therefore large and needs to be taken into account in risk assessment

Sorption Mechanisms of Organic Compounds by Carbonaceous Materials: Site Energy Distribution Consideration

Sorption of naphthalene, lindane, and atrazine on 10 kinds of carbonaceous materials which included four kinds of graphene, three kinds of graphite, two kinds of carbon nanotubes and one kind of mesoporous carbon was investigated. The approximate sorption site energy distributions were calculated based on Dubinin-Ashtakhov (DA) model. The average sorption site energy and standard deviation of the site energy distribution were deduced and applied to analyze the interaction between sorbents and sorbates, and the sorption site heterogeneity. The introduction of oxygen-containing functional groups to the sorbents caused a decrease in their average sorption energy for the studied compounds. However, relative to the decrease in average site energy, the reduction in number of sorption sites as indicated by surface area more strongly reduced their sorption capacity to the tested carbonaceous materials based on the result of the linear regression analysis. Sorption site heterogeneity of the sorbents decreased as their oxygen contents increased, which is attributed to the better dispersion of the oxygen-containing materials as indicated by their TEM images. The method proposed in this study to quantify the average sorption site energy and heterogeneity is helpful for a better understanding of the sorption mechanisms of organic pollutants to carbonaceous materials

Significance of Cooking Oil to Bioaccessibility of Dichlorodiphenyltrichloroethanes (DDTs) and Polybrominated Diphenyl Ethers (PBDEs) in Raw and Cooked Fish: Implications for Human Health Risk

The present study examined the bioacessibility of DDTs and PBDEs in cooked fish (yellow grouper; Epinephelus awoara) with and without heating using the colon extended physiologically based extraction test. The bioaccessibility of DDTs and PBDEs increased from 60 and 26% in raw fish to 83 and 63%, respectively, after the addition of oil to raw fish. However, they decreased from 83 to 66% and from 63 to 40%, respectively, when oil-added fish were cooked. Human health risk assessment based on bioaccessible concentrations of DDTs and PBDEs in fish showed that the maximum allowable daily fish consumption rates decreased from 25, 59, and 86 g day^–1 to 22, 53, and 77 g day^–1 for children, youths, and adults, respectively, after fish were cooked with oil. These findings indicated that the significance of cooking oil to the bioaccessibility of DDTs and PBDEs in food should be considered in assessments of human health risk

Long-Lived Species Enhance Summertime Attribution of North American Ozone to Upwind Sources

Ground-level ozone (O₃), harmful to most living things, is produced from both domestic and foreign emissions of anthropogenic precursors. Previous estimates of the linkage from distant sources rely on the sensitivity approach (i.e., modeling the change of ozone concentrations that result from modifying precursor emissions) as well as the tagging approach (i.e., tracking ozone produced from specific O₃ precursors emitted from one region). Here, for the first time, we tag all O₃ precursors (i.e., nitrogen oxides (NO_<i>x</i>), carbon monoxide (CO), and volatile organic compounds (VOCs)) from East Asia and explicitly track their physicochemical evolution without perturbing the nonlinear O₃ chemistry. We show that, even in summer, when intercontinental influence on ozone has typically been found to be weakest, nearly 3 parts per billion by volume (ppbv) seasonal average surface O₃ over North America can be attributed to East Asian anthropogenic emissions, compared with 0.7 ppbv using the sensitivity approach and 0.5 ppbv by tagging reactive nitrogen oxides. Considering the acute effects of O₃ exposure, approximately 670 cardiovascular and 300 respiratory premature mortalities within North America could be attributed to East Asia. CO and longer-lived VOCs, largely overlooked in previous studies, extend the influence of regional ozone precursors emissions and, thus, greatly enhance O₃ attribution to source region

Suspending Multi-Walled Carbon Nanotubes by Humic Acids from a Peat Soil

Suspension of the pristine and COOH-substituted multi-walled carbon nanotubes (P- and C-MWCNTs) with different outer diameters (ODs) by humic acids (HAs) from a peat soil was examined. Under shaking condition, MWCNTs were not suspended within 5 d. Without HAs, C-MWCNTs were slightly suspended by sonication within 16 h, but no suspension was observed for the pristine ones (P-MWCNTs). HAs greatly enhanced suspension of both P- and C-MWCNTs. The suspension enhancement was attributed to HA sorption, which increased electrostatic repulsion and steric hindrance between individual MWCNTs. Introduction of O-containing hydrophilic moieties to MWCNTs via HA sorption enhanced the interactions of their surfaces with water through H-bonding. Suspending capability of various MWCNTs on suspended mass concentration basis by four HAs showed inconsistent orders with the increasing or decreasing trend of their ODs. However, the suspended surface area concentrations of both P- and C-MWCNTs by individual HAs consistently followed an order of P8 > P30 > P50, and C8 > C30 > C50 (P and C, respectively, refer to P- and C-MWCNTs, and the numbers represent their ODs). These data implied that MWCNTs with smaller OD could be more strongly suspended by a given HA relative to those with larger OD under sonication condition

Sorption of Four Hydrophobic Organic Compounds by Three Chemically Distinct Polymers: Role of Chemical and Physical Composition

The sorption behavior of four hydrophobic organic contaminants (HOCs) (i.e., phenanthrene, naphthalene, lindane, and 1-naphthol) by three types of polymers namely polyethylene (PE), polystyrene (PS), and polyphenyleneoxide (PPO) was examined in this work. The organic carbon content-normalized sorption coefficients (<i>K</i>_oc) of phenanthrene, lindane, and naphthalene by PEs of same composition but distinct physical makeup of domains increased with their crystallinity reduction (from 58.7 to 25.5%), suggesting that mobility and abundance of rubbery domains in polymers regulated HOC sorption. Cross-linking in styrene–divinylbenzene copolymer (PS2) created substantial surface area and porosity, thus, <i>K</i>_oc values of phenanthrene, lindane, naphthalene, and 1-naphthol by PS2 were as high as 274.8, 212.3, 27.4, and 1.5 times of those by the linear polystyrene (PS1). The <i>K</i>_oc values of lindane, naphthalene, and 1-naphthol by polar PPO were approximately 1–3 orders of magnitude higher than those by PS1, and PPO had comparable sorption for phenanthrene but higher sorption for naphthalene and 1-naphthol than PS2. This can be a result that a portion of O-containing moieties in PPO were masked in the interior part, while leaving the hydrophobic domains exposed outside, therefore demonstrating the great influence of the spatial arrangement of domains in polymers on HOC sorption

Costs and Benefits of Household Fuel Policies and Alternative Strategies in the Jing-Jin-Ji Region

Air pollution is still one of the most severe problems in northern China, especially in the Jing-Jin-Ji region around Beijing. In recent years, China has implemented many stringent policies to address the air quality issue, including promoting energy transition toward cleaner fuels in residential sectors. But until 2020, even in the Jing-Jin-Ji region, nearly half of the rural households still use solid fuels for heating. For residents who are not covered by the clean heating campaign, we analyze five potential mitigation strategies and evaluate their environmental effects as well as the associated health benefits and costs. We estimate that substitution with electricity or gas would reduce air pollution and premature mortality more strongly, while the relatively low investment costs of implementing clean coal or biomass pellet lead to a larger benefit–cost ratio, indicating higher cost efficiency. Hence, clean coal or biomass pellet could be transitional substitution options for the less developed or remote areas which cannot afford a total transition toward electricity or natural gas in the short term