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851.
Laboratory incubation trials were conducted to investigate the effects of several factors on the persistence as well as the
dissipation of three synthetic pyrethroid pesticides in red soils obtained from the Yangtze River Delta region in China. The
pyrethroids selected for investigation were cypermethrin, fenvalerate, and deltamethrin, which continue to be used extensively
to control pests on farmland in the region despite the concern that they are highly toxic to certain vertebrate and mammalian
species. Data from this exploratory study showed that the dissipation half-lives (T
1/2) tended to correlate with soil pH and soil organic matter contents, but not with soil cation-exchange capacity. The T
1/2 values were seen to be shorter in soil samples fertilized with glucose than without. The rates of pyrethroid dissipation
also tended to increase with increasing initial soil concentration, but were largely unaffected by whether the pesticides
were present in the soil separately or as a mixture. Another noteworthy observation is that microbial activity appeared to
dominate the degradation process. Findings of this type could offer valuable clues for future research directions in reducing
pesticide persistence in soil, which in turn could lead to the ultimate reduction of environmental pollution caused by pyrethroid
application to farmland in the region.
Project supported by Chinese Academy of Sciences (Project No. KSCX2-YW-N-038) and the National Key Basic Research Support
Foundation (973), China (No. 2002CB4108010). 相似文献
852.
This study focused on the sorption isotherms of 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE) on different original clays (i.e., zeolite, montmorillonite and attapulgite) and organoclay complexes. Sorption of organic pollutants was determined using gas chromatographic (GC) techniques to investigate the sorption behavior, and characterize the effect of, different organic cations. The original clays only sorbed low amounts of p,p'-DDT and p,p'-DDE, and the sorptive curves can be classified as L-shaped. Organoclays exhibited higher amounts of p,p'-DDT and p,p'-DDE sorption. The p,p'-DDT and p,p'-DDE sorption increased with increasing total organic carbon (OC) content of the organoclays. For hexadecyltrimethylammonium (HDTMA)-modified organoclays, the dominant adsorptive medium showed the partitioning sorption of hydrophobic-hydrophobic interaction, indicating no competitive sorption. The sorptive curves can be classified as C-shaped of constant partition (CP). However, benzyltrimethylammonium (BTMA)-modified organoclays exhibited competitive sorption. The sorption isotherm curves can be classified as S-shaped. The sorptive capacity of the HDTMA-modified organoclays for p,p'-DDT were higher than those for p,p'-DDE, but the BTMA-modified organoclays showed a reverse trend. This can be attributed to the different structures and shapes of organic cations, giving different sorptive mechanisms. The p,p'-DDT and p,p'-DDE sorption onto HDTMA-modified organoclays were caused by chemical interaction, with the BTMA modified organoclays occuring due to physical sorption. 相似文献
853.
不同生境条件下苦槠丛枝菌根对根际土壤磷酸酶活性的影响 总被引:4,自引:1,他引:3
以浙江千岛湖和宁波天童两个不同区域内的苦储(Castanopsis sclerophytta)为材料,对处于不同生境条件下的苦槠丛枝菌根(AM)进行了研究.结果表明:两地区土壤pH均处于苦储丛枝菌根生长发育的最适范围内,丛枝菌根的侵染率无明显差异;酸性磷酸酶为两区域内的主导磷酸酶,各种磷酸酶活性均是天童地区高于千岛湖地区;AM侵染率与根际土壤磷酸酶活性之间均呈现正相关,其中天童地区为显著相关,说明AM侵染率对根际土壤磷酸酶活性在某种程度上存在有一定的影响. 相似文献
854.
Simon Garnier Aurélie Guérécheau Maud Combe Vincent Fourcassié Guy Theraulaz 《Behavioral ecology and sociobiology》2009,63(8):1167-1179
We experimentally investigated both individual and collective behavior of the Argentine ant Linepithema humile as they crossed symmetrical and asymmetrical bifurcations in gallery networks. Ants preferentially followed the branch that
deviated the least from their current direction and their probability to perform a U-turn after a bifurcation increased with
the turning angle at the bifurcation. At the collective level, colonies were better able to find the shortest path that linked
the nest to a food source in a polarized network where bifurcations were symmetrical from one direction and asymmetrical from
the other than in a network where all bifurcations were symmetrical. We constructed a model of individual behavior and showed
that an individual’s preference for the least deviating path will be amplified via the ants’ mass recruitment mechanism thus
explaining the difference found between polarized and non-polarized networks. The foraging efficiency measured in the simulations
was three times higher in polarized than in non-polarized networks after only 15 min. We conclude that measures of transport
network efficiency must incorporate both the structural properties of the network and the behavior of the network users. 相似文献
855.
以塔克拉玛干沙漠边缘地区生长的柽柳为研究对象,测定了柽柳灌丛下及周围土壤中Na+和K+含量、电导率、pH值、水分以及柽柳营养枝Na+和K+含量等指标.结果表明,柽柳灌丛造成土壤盐分呈现斑块状分布,形成盐岛.柽柳体内较高的盐分含量可能是造成土壤盐分分布变化的重要因素之一(盐岛效应).相关分析表明,盐岛效应强弱与背景土壤水盐条件密切相关.在背景土水盐条件适中的冲积平原中部,盐岛效应最显著;而在背景土盐分最重的冲积平原中下部和水分含量最低的沙漠边缘,盐岛效应消失.在柽柳生长的适宜地下水位,盐岛效应最明显.柽柳还使冠下土壤Na/K发生改变,碱性增加,含水量降低. 相似文献
856.
Biofuels are sustainable fuels produced from modern biomass such as plants and algae. Biodiesel has high lubricity and ultra-low sulfur content. Biodiesel is produced from vegetable oil by transesterification. Actually, practical biodiesel production is limited by the low reaction rate of transesterification of vegetable oil with methanol catalyzed by CaO. Here we designed an efficient catalyst: benzyl bromide-modified CaO. Using benzyl bromide-modified CaO, we obtained a 99.2 % yield of fatty acid methyl esters in 3 h, compared with 35.3 % yield using commercial CaO under the same reaction conditions. The improved catalytic activity is explained by better fat diffusion to the surface of the benzyl bromide-modified CaO. The novelty of our findings is the much higher yield of our method compared to literature data on heterogeneous catalysis. In addition, the lifetime of our catalyst is excellent. 相似文献
857.
汽车门禁系统已成为汽车智能与安全领域的重要一部分.车主手持智能钥匙靠近汽车,通过车载基站与钥匙的双频通信,实现车门的开与关,还可实现发动机的一键启动.同时,对信号加密采用了改进的AES算法,加入了循环扩展密钥,加大了密码的破解难度.并对整个系统进行了建模仿真,分析了信号传输的误码率.图6,表1,参5. 相似文献
858.
Mehdi Adjeroud Aurélie Guérécheau Jeremie Vidal-Dupiol Jean-François Flot Sophie Arnaud-Haond François Bonhomme 《Marine Biology》2014,161(3):531-541
Clonality and genetic structure of the coral Pocillopora damicornis sensu lato were assessed using five microsatellites in 12 populations from four islands of the Society Archipelago (French Polynesia) sampled in June 2008. The 427 analysed specimens fell into 132 multilocus genotypes (MLGs), suggesting that asexual reproduction plays an important role in the maintenance of these populations. A haploweb analysis of ITS2 sequences of each MLG was consistent with all of them being conspecific. Genetic differentiation was detected both between and within islands, but when a single sample per MLG was included in the analyses, the populations turned out to be nearly panmictic. These observations provide further evidence of the marked variability in reproductive strategies and genetic structure of P. damicornis throughout its geographic range; comparison with results previously obtained for the congeneric species Pocillopora meandrina underlines the importance of life history traits in shaping the genetic structure of coral populations. 相似文献
859.
860.