Distribution, source, and health risk assessment of polycyclic aromatic hydrocarbons in the soils from a typical petroleum refinery area in south China.

The ubiquity of polycyclic aromatic hydrocarbons (PAHs) in soils in petroleum refining areas is an important problem affecting human and ecological safety. In this study, 103 topsoil (0-0.50 m) samples were collected from a retired petroleum refinery area in Guangdong province, south China. The PAHs concentrations were determined by ultrasonic extraction and gas chromatography-mass spectrometry detection methods. Twelve PAHs controlled priority listed by the US Environmental Protection Agency (USEPA) were investigated. The results revealed that the concentration of Æ©12PAHs ranged from 2100 to 5200 µg kg-1, with a mean value of 3741.66 µg kg-1. The site was dominated by high rings PAHs (4-, 5-, and 6-ring), contributing 81.96% to Æ©12PAHs. The concentrations of 9 kinds of PAHs exceeded the Dutch soil quality standard. Besides, the PAHs were primarily distributed in the storage tank area and with high levels of contamination. The results of hierarchical cluster analysis (HCA) and principal component analysis (PCA) indicated that coal combustion was the source of PAHs in topsoil, followed by petroleum dripping and traffic emissions. The incremental lifetime cancer risk (ILCR) modeling illustrated that soil ingestion was the major pathway of PAH exposure for both adults and children. Notably, the total noncarcinogenic human health risk due to PAHs was within the limit of 1, while the carcinogenic risks alone caused by benzo(a)pyrene via soil ingestion to adults and children were obviously beyond the USEPA limit (1.00E -06). Therefore, PAHs in the petroleum refinery areas have potential carcinogenic hazards to human health, the area should be remediated before reuse.

Assessment of heavy metal pollution in soils and health risk consequences of human exposure within the vicinity of hot mix asphalt plants in Rivers State, Nigeria.

This study evaluated the level of heavy metal pollution in soils within the vicinity of hot mix asphalt (HMA) plants and the health risk consequences of human exposure to the heavy metals. Soil samples collected from two asphalt plants during dry and rainy seasons were analyzed for Cr, Co, Cu, Ni, Mn, Cd, Pb, and Zn with atomic absorption spectrophotometer (AAS). Health risk indices were assessed as chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR) while the degree of pollution was assessed with geo-accumulation index (Igeo) and contamination factor (CF). The pollution assessment revealed that the soil samples were moderately to highly polluted with Cd. In both seasons, Zn and Mn, respectively, had the highest CDI values for ingestion, inhalation, and dermal route for both asphalt plants while Cd has the least CDI values for all the routes in both plants. The HQ and HI values for all the metals were less than 1.00E + 00 indicating no non-carcinogenic risk from exposure to any of the metals. Furthermore, the dermal route was found to be the least likely model for health risks associated with human exposure to soil heavy metals within the vicinity of the plants. The CR values for the metals were also within threshold value indicating non-significant cancer risk from exposure to the metals. Though no significant health risks were observed in the study, clean and efficient production of hot mix asphalt should be encouraged to minimize health risks and environmental pollution during production and usage.

Adsorption of Polycyclic Aromatic Hydrocarbons from aqueous solution by Organic Montmorillonite Sodium Alginate Nanocomposites.

The adsorption method is generally considered a promising technique to remove inorganic and organic contaminants in an economically and environmentally friendly superior manner. In this study, organic montmorillonite sodium alginate composites were prepared, in which, montmorillonite and cationic surfactant (cetyltrimethylammonium bromide, CTAB) in different added amounts were coagulated with sodium alginate using CaCl2 as the crosslinking agent. The morphological properties of the composites were characterized thoroughly and employed in three typical target pollutants of polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, fluorene, and phenanthrene) by batch adsorption experiments from aqueous solution. The composites provide an efficient alternative for PAHs removals. The composites could be stably separated and regenerated with methyl alcohol. Furthermore, the adsorption kinetic and isotherm data were well described by the Elovich kinetic and the Freundlich isotherm model, respectively. According to these, the adsorption process occurred via multilayer adsorption on the composite's energetically heterogeneous surface. Moreover, pore diffusion and hydrophobicity played a dominant role in the adsorption mechanism. Overall, our study offers a developed adsorbent that has the advantage of being recyclable, low cost, biodegradable and biocompatible for effectively removing PAHs from aqueous solution.

Characteristics of cadmium accumulation and isotope fractionation in higher plants.

Cadmium (Cd) pollution of the soil is an important global environmental issue owing to its great toxicity. The study of metal isotope fractionation is a novel technique that could be used to identify and quantify metal uptake and transport mechanisms in plant. In this study, cadmium tolerant Ricinus communis and hyperaccumulator Solanum nigrum have been cultured in different Cd concentration nutrient solutions. The Cd isotope values, metal elements concentrations in the organs (root, stem and leaf) in the two plant species have been measured during the growth periods (10d, 15d, 20d, 25d, and 30d). The results indicate that the organs of S. nigrum could be enriched with lighter Cd isotopes compared with R. communis. In addition, the Cd isotope fractionation become smaller when the plants were subjected to high Cd toxicity, which indicates that Cd isotope fractionation reflected the extent of Cd toxicity to plants. This study advances our current view of Cd translocation machination in plants.

Stable isotope fractionation during uptake and translocation of cadmium by tolerant Ricinus communis and hyperaccumulator Solanum nigrum as influenced by EDTA.

The isotopic fractionation could contribute to understanding the Cd accumulation mechanisms in plant species. However, there are few of systematical investigations with regards to the Cd isotope fractionation in hyperaccumulator plants. The Cd tolerant Ricinus communis and hyperaccumulator Solanum nigrum were cultivated in nutrient solutions with varying Cd and EDTA concentrations. Cd isotope ratios were determined in the solution, root, stem and leaf. The two investigated plants were systematically enriched in light isotopes relative to their solutions (Δ114/110Cdplant-solution = -0.64‰ to -0.29‰ for R. communis and -0.84‰ to -0.31‰ for S. nigrum). Cd isotopes were markedly fractionated among the plant tissues. For both plant species, an enrichment in light Cd isotopes from solution to root was noted, followed by a slight depletion in light Cd isotopes from root to shoot. Noticeably, the chelation process has caused lighter Cd isotope enrichment in the root of R. communis and S. nigrum. Further, the good fits between △114/110Cdroot-plant and ln Froot (or between △114/110Cdshoot-plant and ln Fshoot) indicate that Cd isotopic signatures can be used to study Cd transportation during the metabolic process of plants. This study suggests that knowledge of the Cd isotope ratios could also provide new tool for identifying the Cd-avoiding crop cultivars.

Heavy metal contents and enrichment characteristics of dominant plants in wasteland of the downstream of a lead-zinc mining area in Guangxi, Southwest China.

A field investigation on the content of heavy metals in soils and 17 kinds of dominant plants from wasteland of the downstream of a Pb-Zn mine in Northwest Guangxi Zhuang Autonomous Region was carried out. The absorption and accumulation characteristics of heavy metals between plants and soil were compared, and the candidate species for ecosystem restoration of the area were selected. The results indicated that the soils had been subjected to pollution of heavy metals in varying degrees. The concentrations of Cd, Pb, Zn were 46.5, 57.3 and 23.7 times higher than their corresponding background values, respectively. The contents of Cd, Pb and Zn in the most analyzed plants exceed the normal ranges and the phytotoxic level. C. crepidioides, S. nigrum, B. pilosa, C. Canadensis, A. conyzoides, I. denticulata and E. crusgali showed strong capability in accumulation and transport of Cd, and they could be used as good candidates for Cd- phytoextraction. Among which, Cd concentration in the aerial part of C. crepidioides exceeded the threshold of Cd-hyperaccumulator. Thus, C. crepidioides demonstrated the basic characteristics of a Cd-hyperaccumulator. The lower translocation ratios for Cd, Cu, Zn and Pb in P. vittata and C. chinensis make them suitable for phytostabilization in the study area.

Characteristics, source, and potential ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the Songhua River Basin, Northeast China.

The concentration characteristics, sources, and potential ecological risk assessment of 16 PAHs were investigated in the surface water from the Songhua River Basin, Northeast China. A total of 48 river water samples, including 16 from the main streams and 32 from the tributaries, were collected. Samples were separated into dissolved phases and suspended particle matter (SPM) via filtration with 0.47 µm glass fiber filters. Each phase was analyzed for PAHs. The total PAH concentration in the dissolved phase in the water ranged from 32.5 to 108 ng L-1 and from 0.3 to 62.3 µg g-1 (dry weight) in the suspended particle matter (SPM). The total PAH concentration in the main stream was lower than in the tributaries; the volume of annual runoff of rivers had a significant effect on the Æ©PAH in the rivers. The 2- and 3-ring PAHs dominated in both the dissolved phase and SPM, indicating a relatively recent local source of PAHs in the study area. The concentrations of PAHs in the Songhua River Basin are lower when compared with the values previously reported in the literature from other rivers around the world. The sources of PAHs were assessed by diagnostic ratios and principal component analysis (PCA), and the ecological risk of the PAHs was assessed based on the risk quotient (RQ). The diagnostic ratios and PCA indicated that the main sources of PAHs originated from pyrogenic and petrogenic sources, and pyrogenic sources had a greater impact. The ecological risk assessment indicated that the PAHs presented low ecosystem risk in the Songhua River Basin.

Mechanism of dialkyl phthalates removal from aqueous solution using γ-cyclodextrin and starch based polyurethane polymer adsorbents.

Phthalate esters have been known as potent endocrine disruptors and carcinogens; and their removal from water have been of considerable concern recently. In the present study, γ-cyclodextrin polyurethane polymer (GPP), γ-cyclodextrin/starch polyurethane copolymer (GSP), and starch polyurethane polymer (SPP) have been synthesized and characterized. Their adsorption efficiencies for the removal of dimethyl phthalate (DMP) and diethyl phthalate (DEP) from aqueous solutions were investigated. The characterization results showed the success of the synthesis. The isotherms were L-type, and both the Langmuir and Freundlich adsorption isotherm gave good fittings to the adsorption data. Adsorption mechanisms suggested that these adsorbents spontaneously adsorb phthalate molecules driven mainly by enthalpy change, and the adsorption process was attributed to multiple adsorbent-adsorbate interactions such as hydrogen bonding, π-π stacking, and pore filling. The results showed that starch and γ-cyclodextrin polyurethane polymer adsorbents have excellent potential as adsorbent materials for the removal of phthalates from the contaminated water.

Cross-linked starch-based polymer as an SPE material for the determination of nitrophenols at trace levels in environmental water.

SPE using a cross-linked starch-based polymer (CSMDI) as an adsorbent for the determination of four nitrophenols at trace levels from aqueous solution was investigated. The CSMDI was synthesized from native starch using 4,4'-methylenebisphenyldiisocyanate as a cross-linking agent in dry DMF. Parameters affecting the extraction efficiency including the pH of the water sample, type of eluent and its volume, flow rate, sample volume, and methanol content were investigated and optimized. The optimized results exhibited excellent linear relationships (R(2) > 0.995) for all the nitrophenols over the range of 2.0-200 ng/mL, with the RSD values in the range of 2.9-5.7% (n = 5). The LODs ranged from 0.08-0.34 ng/mL (S/N = 3) for the four nitrophenols tested under optimum conditions. The developed method has been successfully applied for the analysis of several real environmental water samples including tap, river, and reservoir water. These results indicated that the CSMDI had a tremendous potential for the enrichment and determination of nitrophenols at trace levels in environmental water samples.

Application of quantum descriptors for predicting adsorption performance of starch and cyclodextrin adsorbents.

Adsorption trend of aromatic compounds on epichlorohydrin (EPI), 1,6-hexamethylene diisocyanate (HDI), and 4,4-methylene diphenyl diisocyanate (MDI) cross-linked starch and cyclodextrin adsorbents were comparatively studied by density functional theorem (DFT) based interaction descriptors and batch adsorption studies. The DFT quantum chemical descriptors predicted adsorption trend of MDI adsorbents>HDI adsorbents>EPI adsorbents. The values of the fractional number of electrons transferred (ΔN) for all the studied adsorbent-adsorbate pair were negative, indicating that the adsorbents were electron donors in the studied adsorption interaction. The batch adsorption performance for the studied cross-linked adsorbents was in agreement with the DFT predictions. Energy gap, chemical hardness, and softness showed good linear correlation (R(2)=0.8,073 ± 0.2259) to the batch adsorption performance for most of the studied adsorbent-adsorbate pairs. The present study demonstrated that DFT quantum chemical parameters are suitable adsorption descriptors for predicting adsorption performance of cross-linked adsorbents.