[QSPR study on the lipid-water partition coefficients of dioxins based on DFT].

With computational method of density functional theory (DFT), quantified model study of equilibrium partitioning properties of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) between lipid phase of organism (Poecilia reticulata) and water phase was carried out based on quantum chemical and further calculated parameters, namely frontier orbital energies, entropies, traceless quadrupole moments as well as molecular absolute hardness, electronegativities and electrophilicity indices, which all were derived from full geometry optimization of PCDD/Fs. Through multiple linear regression (MLR) analyses, quantitative structure-property relationship (QSPR) was successfully proposed in the form of multi-parameter quadratic function: lgK(hw) = 5.343 - 0.001(S - 125.480)(2) - 0.355(omega - 3.239)(2) + 0.006( Q = - 2.950)(2) - 22.728(eta - 2.365)(2). It was shown that the obtained QSPR had higher goodness of fitting and robustness, determination coefficient and cross-validated correlation coefficient being 0.943 and 0.908 respectively, and it was also provided with ideal interior and exterior predictive abilities so that it could be used for prediction of unknown lipid-water partitioning properties. By comparison, QSPR in this research was superior to that from previous SOFA (solubility parameter for fate analysis) method on the whole. Lipid-water partitioning properties (coefficients) of PCDD/Fs should be mainly related to molecular volume and aryl hydrocarbon molecular interactions determined by charge distribution. To a certain degree, they also might be influenced by potential biotransformation and molecular reactivity.

[Effect of low-molecular-weight organic carbon on anaerobic degradation and volatilization of hexachlorobenzene in soils].

Batch incubation experiments in aid of anaerobic incubation flask were conducted to study the anaerobic degradation and volatilization of hexachlorobenzene (HCB), the change of pH in soil, the emission of CH4 and CO2, and the volatilization of HCB in the Hydragric Acrisol and Gleyi-Stagnic Anthrosol added with acetic acid, glucose and citric acid. Results showed that HCB was reduced by 20%-44% in Hydragric Acrisol during 8 weeks, and addition of acetic acid inhibited the dechlorination, indicating that dechlorination was impeded at low pH. Addition of glucose or citric acid decreased the dechlorination rate initially and then increased it. HCB was reduced by 21%-23% in Gleyi-Stagnic Anthrosol, and there was no obvious effect by adding low-molecular-weight organic carbon. The main product of HCB anaerobic dechlorination was pentachlorobenzene (PCB), which were 23-96 microg/kg and 64-92 microg/kg in Hydragric Acrisol and Gleyi-Stagnic Anthrosol respectively. Furthermore, the degradation of HCB had no statistically significant correlation with the productions of CH4 and CO2. Addition of low-molecular-weight organic carbon reduced HCB volatilization, which was stronger in Hydragric Acrisol than in Gleyi-Stagnic Anthrosol, indicating that soil organic matter was an important factor in HCB volatilization.

Aging activity of DDE in dissimilar rice soils in a greenhouse experiment.

A green-house study was conducted in late 2005 to investigate the aging behavior of p,p'-DDE in two types of soil, Hydragric Anthrosols (An) and Hydragric Acrisols (Ac), according to the World Reference Base (WRB) [FAO/ISRIC/ISSS. 1998. World reference base for soil resources. World soil resources reports, Rome. p. 87]. Paddy rice and dry rice were grown in submerged paddy soils and non-submerged upland soils, respectively. The concentration of extractable p,p'-DDE in fresh DDE-spiked soils was 746.2ngg(-1). During the first few weeks of the experiment, the extractability of p,p'-DDE became increasingly low as the aging period prolonged. However, certain amount of p,p'-DDE that had been captured by soil minerals and organic matter (OM) could be released and became extractable in the later period. The extractability of p,p'-DDE in submerged soils was significantly lower than that in non-submerged soil, because flooding could increase the binding of pollutants to soil particles. The plantation of both dry rice and paddy rice slowed down the aging process of p,p'-DDE. After one month's growth of rice, p,p'-DDE bound to soil particles was released and became extractable. The OM and silt content of An are higher than that of Ac, resulting in more bound residues and relative lower extractability of p,p'-DDE in An. In addition, the extractability of p,p'-DDE could be reduced by the addition of rice straw to soils.

Organochlorine pesticides in soils under different land usage in the Taihu Lake region, China.

A field study was conducted in the Taihu Lake region, China in 2004 to reveal the organochlorine pesticide concentrations in soils after the ban of these substances in the year 1983. Thirteen organochlorine pesticides (OCPs) were analyzed in soils from paddy field, tree land and fallow land. Total organochlorine pesticide residues were higher in agricultural soils than in uncultivated fallow land soils. Among all the pesticides, sigmaDDX (DDD, DDE and DDT) had the highest concentration for all the soil samples, ranging from 3.10 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and followed by sigmaHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and alpha-endosulfan were also found in soils with less than 15 ng/g. Ratios of p,p'-(DDD+DDE)/DDT in soils under three land usages were: paddy field > tree land > fallow land, indicating that land usage influenced the degradation of DDT in soils. Ratios of p,p'-(DDD+DDE)/DDT > 1, showing aged residues of DDTs in soils of the Taihu Lake region. The results were discussed with data from a former study that showed very low actual concentrations of HCH and DDT in soils in the Taihu Lake region, but according to the chemical half-lives and their concentrations in soils in 1980s, the concentration of DDT in soils seemed to be underestimated. In any case our data show that the ban on the use of HCH and DDT resulted in a tremendous reduction of these pesticide residues in soils, but there are still high amounts of pesticide residues in soils, which need more remediation processes.

Relationships between humic substance-bound mercury contents and soil properties in subtropical zone.

The bioavailability of humic substance-bound mercury (HS-Hg) has been established, while the distribution of HS-Hg in soils in relation to soil properties remains obscure. Path analysis and principal component analysis were employed in present study to investigate how soil factors influence the contents of HS-Hg in soils. Results showed that HS-Hg ranged from 0.0192 to 0.2051 mg/kg in soils. The two fractions existed in soils as humic acid-bound mercury (HA-Hg) > fulvic acid-bound mercury (FA-Hg) and the ratio of HA-Hg/FA-Hg was 1.61 on the average. Soil organic carbon (OC) and HS favorably determined soil HS-Hg and the two fractions. The mercury source forming HS-Hg derived from soil total mercury and HS-Hg. FA-Hg and HA-Hg served as mercury source for each other. In acidic soils, FA-Hg and HA-Hg consistently rose with the increase of OC, and generally HA-Hg increased more dramatically. Soils with lower pH and lighter texture contained more HS-Hg, particularly fraction of FA-Hg. Among all influencing factors, organic material source showed the strongest effect, followed by other soil properties and soil mercury source.

[Hysteretic characteristics of atrazine desorption from fluvo-aquic soil].

Kinetic batch experiments are carried out in order to investigate the effects of a wide range of atrazine initial concentrations and consecutive desorption time on the desorption characteristics of atrazine from fluvo-aquic soil. The results reveal that, atrazine concentrations in soil solution gradually decreased with desorption time increasing, whose relationship can be expressed with empirically exponential functions. After consecutive five steps (or 5 days), when atrazine initial concentrations increased from 50 microg x L(-1) to 2000 microg x L(-1), the average desorption percentages were 23.1%, 30.4%, 33.0%, 36.4% and 38.5%, respectively. The relationships between the amount of atrazine adsorbed by soil colloids and corresponding atrazine concentrations in soil solutions may be described through the traditional and time-dependent desorption isotherms. The obvious discrepancies in two families of both traditional and time-dependent desorption isotherms from adsorption isotherm, which retention time last for 168 hours before commencement of desorption, were indicative of hysteresis. Two sets of Freundlich parameters derived from both desorption isotherms can quantify the hysteresis between desorption and adsorption isotherms. However, hysteresis coefficient, omega, was applicable only for the traditional desorption isotherms, H and lamda applicable for both.

[Therapeutic effect of infrared radiation on skin scald in rats].

OBJECTIVE: To investigate the therapeutic effect of infrared radiation (IR) on the skin scald in rats. METHODS: Thirty-nine male Wistar rats were used in the study, and they were randomly divided into normal control (C, n = 13), scald (S, n = 13, no treatment after scalding) and treatment (T, n = 13, with IR radiation treatment for 5 days since 2nd post scalding day (PSD) groups. The rats in S and T groups were subjected to deep partial thickness scalding on the back. The cutaneous tissue samples from rat wound in each group were harvested on the 3rd and 7th PSD for pathomorphological examination. DNA synthesis in wound tissue was analyzed by 3H-TdR incorporation method, and the vascular permeability in cutaneous tissue, degree of tissue edema and MDA content were determined by corresponding methods. RESULTS: Epidermal exfoliation, cutaneous ulcer, follicular atrophy and damage, and massive formation of collagen were identified in the skin wound of rats in S group on the 7th PSD compared with C group. The skin in T group was smooth with slight atrophy and a few collagen fibers in follicles. The 3H-TdR incorporation amount in the rats in T group (1856.33 +/- 343.81 cpm/mg) on the 7th PSD was significantly higher than that in S group (1353.95 +/- 274.48 cpm/mg) (P < 0.01). The tissue permeability, edema degree and MDA content in the cutaneous tissue in S group were obviously higher than those in group C, while these indices were markedly lower in T group when compared with those in S group (P < 0.01-0.001). CONCLUSION: Treatment with IR seemed to be beneficial to the promotion of skin tissue metabolism and tissue repair.