Application of portable gas chromatography-photo ionization detector combined with headspace sampling for field analysis of benzene, toluene, ethylbenzene, and xylene in soils.

A method based on headspace (HS) sampling coupling with portable gas chromatography (GC) with photo ionization detector (PID) was developed for rapid determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) in soils. Optimal conditions for HS gas sampling procedure were determined, and the influence of soil organic matter on the recovery of BTEX from soil was investigated using five representative Chinese soils. The results showed that the HS-portable-GC-PID method could be effectively operated at ambient temperature, and the addition of 15 ml of saturated NaCl solution in a 40-ml sampling vial and 60 s of shaking time for sample solution were optimum for the HS gas sampling procedure. The recoveries of each BTEX in soils ranged from 87.2 to 105.1 %, with relative standard deviations varying from 5.3 to 7.8 %. Good linearity was obtained for all BTEX compounds, and the detection limits were in the 0.1 to 0.8 µg kg(-1) range. Soil organic matter was identified as one of the principal elements that affect the HS gas sampling of BTEX in soils. The HS-portable-GC-PID method was successfully applied for field determination of benzene and toluene in soils of a former chemical plant in Jilin City, northeast China. Considering its satisfactory repeatability and reproducibility and particular suitability to be operated in ambient environment, HS sampling coupling with portable GC-PID is, therefore, recommended to be a suitable screening tool for rapid on-site determination of BTEX in soils.

Recent progress on in-situ chemical oxidation for the remediation of petroleum contaminated soil and groundwater.

Accidental oil leaks and spills can often result in severe soil and groundwater pollution. In situ chemical oxidation (ISCO) is a powerful and efficient remediation technology. In this review, the applications and recent advances of three commonly applied in-situ oxidants (hydrogen peroxide, persulfate, and permanganate), and the gap in remediation efficiency between lab-scale and field-scale applications is critically assessed. Feasible improvements for these measures, especially solutions for the 'rebound effect', are discussed. The removal efficiencies reported in 108 research articles related to petroleum-contaminated soil and groundwater were analyzed. The average remediation efficiency of groundwater (82.7%) by the three oxidants was higher than that of soil (65.8%). A number of factors, including non-aqueous phase liquids, adsorption effect, the aging process of contaminants, low-permeability zones, and vapor migration resulted in a decrease in the remediation efficiency and caused the residual contaminants to rebound from 19.1% of the original content to 57.7%. However, the average remediation efficiency of ISCO can be increased from 40.9% to 75.5% when combined with other techniques. In the future, improving the utilization efficiency of reactive species and enhancing the contact efficiency between oxidants and petroleum contaminants will be worthy of attention. Multi-technical combinations, such as the ISCO coupled with phase-transfer, viscosity control, controlled release or natural attenuation, can be effective methods to solve the rebound problem.

[Heavy Metals Pollution in Topsoil from Dagang Industry Area and Its Ecological Risk Assessment].

Based on previous studies and field investigation of Dagang industry area in Tianjin, a total of 128 topsoil samples were collected, and contents of 10 heavy metals (As, Cd, Cr, Co, Cu, Pb, Ni, V, Zn and Hg) were determined. The geoaccumulation index and geostatistics were applied to examine the degree of contamination and spatial distribution of heavy metals in topsoil. The assessment on ecological risk of heavy metals was carried out using Hakanson's method, and the main resources of the heavy metals were analyzed as well. It was found that As, Cd and Co had the highest proportions exceeding Tianjin background value, which were 100%, 97.66% and 96.88%, respectively; the heavy-metal content increased to some extent comparing with that in 2004, and the pollutions of As and Cd were the worst, and other metals were at moderate pollution level or below. The ecological risks of heavy metals were different in topsoil with different land use types, the farmland soil in the southwest as well as soils adjacent to the industrial land were at relatively high potential ecological risk level, and the integrated ecological risk index reached up to 1 437.37. Analysis of correlation and principal component showed that traffic and transportation as well as agricultural activities might be the main resources of heavy metals in the area, besides, the industrial activities in the region might also affect the accumulation of heavy metals.

[Microstructure morphology and flocculation mechanism of the decolorizing flocculant poly-aluminum (III)-magnesium (II)-sulfate].

Crystal structures and morphologic characteristics of poly-aluminum (III)-magnesium (II)-sulfate (PMAS) were discussed using X-radial diffraction and infrared spectrogram and the flocculation mechanism was explored here based on comparisons between decolorization effect of landfill leachate secondary effluent and the system Zeta potential. The results indicated that PMAS was a kind of macromolecular composite polymer of aluminum and magnesium based on -OH bonding. The flocculation mechanism of PMAS was mainly charge neutralization and co-precipitation netting. Charge neutralization was the main mechanism at low dose. Its flocculation behaviors were different along with different pH of wastewater at high doses, namely, it was mainly charge neutralization at low pH and co-precipitation netting at high pH and both of them work together at neutral condition.

[Research on the characteristic of toluene migration and distribution in fluvoaquic soil and its simulation using STOMP model].

Frequently accidental spill of hazard materials into soil environment posed significant threats to human health and natural environment in China. In this paper, simulated nonaqueous phase liquid (NAPLs) toluene sudden spill in fluvo-aquic soil was performed in a two-dimensional tank to investigate the migration and distribution characteristics of toluene as well as its simulation through STOMP model. Visual observation showed that the horizontal expansion of toluene with concentration > 1 g x kg(-1) and > 20 g x kg(-1) were approximate 2.3 and 3 times the length of the corresponding vertical transportation, respectively. The result revealed that toluene exerted a preferential tendency to lateral spread compared to the vertical migration trends, which may contribute to the impeding effect as a result of the low permeable capacity of soil (permeability coefficient was 0.12 cm x h(-1)). The behavior and fate of toluene in heterogeneous soil layers (combined fluvo-aquic-sand and sand-fluvo-aquic soil layers, respectively) after spill were simulated using STOMP model and the results indicated that the significant difference in relative permeability of interface layer, due to the much higher value of permeability coefficient of sand (29.70 cm x h(-1)) than that of fluvo-aquic soil, played an important role on the redistribution of toluene after its spill into the heterogeneous soil layers. For practical purposes, the results of this study may be beneficial to identify the distribution property of NAPLs in time after its release into the soil environment.

[Chemical speciation of rare metals in three natural soils of China].

Soil profile samples of isohumosol, primosol, and ferrosol were obtained in relatively clean areas of China. Concentrations and chemical speciation of rare metals [e.g., Ag (Silver), Bi (Bismuth), In (Indium) and Sn (Tin)] were determined, in which sequential extraction was used to fraction metals. Vertical distributions of elemental enrichment ratios (ERs) were used to study the anthropogenic influence. The mobility of metals was characterized by the sum of exchangeable form and carbonate-bound form. Average concentrations of Ag, Bi, In and Sn in the A horizon were (0.14 +/- 0.01), (0.49 +/- 0.09), (0.050 +/- 0.01), and (2.8 +/- 0.9) mg x kg(-1), respectively. The ERs were close to 1. Average distributions of metal speciation were: Ag, residual (65.8%) > H202-extractable organically bound (H2O2-Org) (25.9%) > Amorphous metal oxide-bound (am-MeOx) (4.2%) > Metal-organic complex-bound (Me-Org) approximately Crystalline Fe oxide-bound (cr-FeOx) (2.0%); Bi, residual (29.2%) > H2O2-Org (27.1%) > cr-FeOx (22.7%) > am-MeOx (18.8%) > Me-Org (1.0%) > carbonate-bound (0.9%) > easily reducible metal oxide-bound (re-MeOx) (0.3%); In, residual (67.8%) > cr-FeOx (17.0%) > am-MeOx (6.8%) > H2O2-Org (6.0%) > carbonate-bound (1.4%) > Me-Org (1.0%); Sn, residual (58.1%) > am-MeOx (23.0%) > cr-FeOx (15.6%) > H2O2-Org (1.8%) > Me-Org (1.1%) > exchangeable approximately carbonate-bound (0.2%). the results indicated that the exogenous elements enrichment was deficiency to minimal, and the concentrations of the rare metals were close to background values of soil in studied areas. Rare metals were stable in soils. The mobility of metals was in the order In > Bi > Sn > Ag.

[Health risk analysis of VOC/SVOC contaminated soil in an abandoned chemical plant].

Environmental health risk of contaminated soil in a typical abandoned industry was analyzed based on the full field investigation according to the site assessment procedure of American Society for Testing and Material (ASTM). Parameters were modified with the combination of Chinese crowd character and site specifics. Results indicated that the site was mainly contaminated with volatile and semi-volatile organic compounds in soil profiles. And the contents of carbon tetrachloride, tetrachloroethylene, pentachloroethane, hexachlorobutadiene, hexachloroethane and hexachlorobenzene in soil samples were exceeded the national environmental standard. These contaminants ranked the carcinogenic risks and hazard quotients more than 10(-2) and 1 in some locations with the exposure by oral ingestion, dermal contact and inhalation. Contaminants in this site had resulted in the high health risks to the residents and surrounding communities. The risk should be reduced to the health acceptable level by the treatment and remediation before further development for residential and commercial utilization.

[Synergy effect of dissolved oxygen in photodegradation of propisochlor in aqueous solution].

The synergetic effect of dissolved oxygen (DO) in the photodegradation of propisochlor aqueous solution was investigated in the presence of UV. With the increase of dissolved oxygen concentration, from 0 to 7.5 mg/L, photodegradation of propisochlor was accelerated. After the concentration of 7.5 mg/L, the rate and efficiency of photodegradation stopped increasing and began to decrease when the concentration became higher. During the photolysis process, dissolved oxygen was consumed. It suggested that the oxygen took an active part in the photolysis. It was found by analysis that the pohtolysis products under different dissolved oxygen concentrations were almost the same, but the production of several products was different. Singlet oxygen (1O2) as the resonance intermediate in the photolysis systems was confirmed by electron spin resonance spin trapping experiments.