F.L. Xu

Use of sequential ASE extraction to evaluate the bioavailability of DDT and its metabolites to wheat roots in soils with various organic carbon contents

An accelerated solvent extraction (ASE) procedure using water, n-hexane and a mixture of n-hexane and acetone as solvents in sequence was developed and tested to evaluate the bioavailability of DDT and its metabolites including p,p-DDT, o,p-DDT, p,p-DDE, and p,p-DDD (SigmaDDTs) to wheat uptake from soils characterized by varied organic carbon contents. Results indicated that the extractability of SigmaDDTs with water was enhanced considerably in the presence of water soluble organic carbon (WSOC), while the amount of SigmaDDTs extracted with n-hexane was negatively correlated to the content of water insoluble organic carbon (WIOC). The interaction between SigmaDDTs and WIOC also reduced the bioavailability of the pesticides to wheat roots during uptake. There was a good positive correlation between the amount of SigmaDDTs extracted by n-hexane and the amount of SigmaDDTs accumulated in wheat roots, suggesting some potential for the use of the n-hexane ASE-extracted fraction as an indicator of SigmaDDTs bioavailability to plant uptake. As such, the three sequentially extracted fractions may be viewed as representing the mobile, bioavailable, and fixed pools of SigmaDDTs in the soil.

Chapter 10 – Fractionation and bioavailability of copper, cadmium and lead in rhizosphere soil

ABSTRACT Chemical forms of copper, cadmium and lead in the rhizosphere of several plant species were investigated using rhizobox cultivation, sequential extraction and a set of specially designed experiments to examine dynamic changes in metal fractionation and bioavailability in the rhizosphere, and to experimentally evaluate the factors governing the variation in metal fractionation. The results from the dynamic change experiments demonstrated that there were continuous changes in metal fractionation within the maize rhizosphere. Initially, the amount of exchangeable copper and cadmium increased before dropping toward or below the initial levels after 40–70 days. Carbonate-associated copper followed a similar trend, but at a slower pace than the exchangeable fraction, while carbonate-bound cadmium and lead leveled off after an initial increase. The accumulation of the metals in the maize plant showed biomass-dependent characteristics. The amount of metals accumulated inside the plant material exceeded the initial quantity of the exchangeable metals in the soil, indicating a transformation from less bioavailable to more bioavailable forms. During cultivation, a decrease in redox potential, increases in pH and microbial activity, and an increase followed by a decrease in dissolved organic carbon in the maize rhizosphere were observed. The increase pattern of exchangeable copper and cadmium was affected by the relative magnitude of mobilization and bioaccumulation, which occured in opposite directions. The effects of acidification, alkalization and generation of root exudates were studied by the addition of acid, alkali or root exudates from the solution cultures of several plants to soil prior to incubation, and metal fractionation measurements. Changes in metal fractionation in the rhizospheres of unsterilized and sterilized soils were studied using rhizoboxes cultivated with seedlings of maize, wheat, pea and soybean. The comparison was also conducted for the soil receiving root exudate from solution cultures of the four plant species. For the calcareous soil and the plant species studied, pH was not the main cause of the corresponding alterations. The resulting significant influence of root exudates on metal fractions appears to have been brought about through complexation rather than acidification. Microbial activity also had significant effects on the metal fractionation changes.

Macrophage-Mediated Effects of Airborne Fine Particulate Matter (PM2.5) on Hepatocyte Insulin Resistance in Vitro

Fine particulate matter (PM2.5) pollution poses significant health risks worldwide, including metabolic syndrome-related diseases with the characteristic feature of insulin resistance. However, the mechanism and influencing factors of this effect are poorly understood. In this serial in vitro study, we aimed at testing the hypothesis that macrophage-mediated effects of PM2.5 on hepatic insulin resistance depend on its chemical composition. Mouse macrophages were exposed to PM2.5 that had been collected during summer or winter in Beijing, which represented different compositions of PM2.5. Thereafter, hepatocytes were treated with macrophage-conditioned medium (CM). PM2.5 induced interleukin-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 expression and secretion in macrophages, particularly after winter PM2.5 exposure. Correspondingly, winter CM weakened hepatocellular insulin-stimulated glucose consumption. Further investigation revealed that the normal insulin pathway was suppressed in winter CM-treated hepatocytes, with increased phosphorylation of insulin receptor substrate 1 at serine residue 307 (Ser307) and decreased phosphorylation of protein kinase B (PKB/AKT) and forkhead box transcription factor O1 (FoxO1). Moreover, c-Jun N-terminal kinase, a key moderator of the sensitivity response to insulin stimulation, was activated in hepatocytes treated with winter CM. Although further studies are warranted, this preliminary study suggested an association between PM composition and insulin resistance, thus contributing to our understanding of the systemic toxicity of PM2.5.

Seasonal variations in fine particle composition from Beijing prompt oxidative stress response in mouse lung and liver

Exposure to air pollution can induce oxidative stress, inflammation and adverse health effects. To understand how seasonal and chemical variations drive health impacts, we investigated indications for oxidative stress and inflammation in mice exposed to water and organic extracts from urban fine particles/PM2.5 (particles with aerodynamic diameteru202f≤u202f2.5u202fμm) collected in Beijing, China. Higher levels of pollution components were detected in heating season (HS, winter and part of spring) PM2.5 than in the non-heating season (NHS, summer and part of spring and autumn) PM2.5. HS samples were high in metals for the water extraction and high in polycyclic aromatic hydrocarbons (PAHs) for the organic extraction compared to their controls. An increased inflammatory response was detected in the lung and liver following exposure to the organic extracts compared to the water extracts, and mostly in the HS PM2.5. While reduced antioxidant response was observed in the lung, it was activated in the liver, again, more in the HS extracts. Nrf2 transcription factor, a master regulator of stress response that controls the basal oxidative capacity and induces the expression of antioxidant response, and its related genes were induced. In the liver, elevated levels of lipid peroxidation adducts were measured, correlated with histologic analysis that revealed morphologic features of cell damage and proliferation, indicating oxidative and toxic damage. In addition, expression of genes related to detoxification of PAHs was observed. Altogether, the study suggests that the acute effects of PM2.5 can vary seasonally with stronger health effects in the HS than in the NHS in Beijing, China and that some secondary organs may be susceptible for the exposure damage. Specifically, the liver is a potential organ influenced by exposure to organic components such as PAHs from coal or biomass burning and heating.

Effects on IL-1β signaling activation induced by water and organic extracts of fine particulate matter (PM 2.5 ) in vitro

Fine particulate matter (PM2.5) air pollution poses a major risk to human health worldwide, and absorbed chemicals play a key role in determining the toxicity of PM2.5. After inhalation and entry into the lungs, PM2.5 components induce pro-inflammatory cytokines (e.g., interleukin (IL)-1β) in pulmonary cells. To test whether PM2.5 components induce IL-1β through signing pathways that include the toll-like receptor 4 (TLR4)/nuclear factor-κ-gene binding (NF-κB), nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3), we exposed the mouse macrophage cell-line RAW264.7 to both water and organic extracts of PM2.5 sampled over a 1-year period in Beijing, China. Varying degrees of oxidative stress and inflammatory responses were induced following exposure, while organic extracts of PM2.5 collected during the heating season induced more significant responses. This response is attributed to high concentrations of polycyclic aromatic hydrocarbons (PAHs) originating from coal combustion and biomass burning for domestic heating. The inhibition of signaling molecules suggested that increased IL-1β was associated with the TLR4/NF-κB pathway and NLRP3 inflammasome activation, with a slightly difference between water and organic extracts exposure groups, which was likely the result of different chemical components. Our study elucidated a potentially important mechanism by which PM2.5 components could trigger pulmonary inflammation, thus improving our understanding of the deleterious effects of this important and prevalent form of air pollution.