Sources, distribution, and risk assessment of organochlorine pesticides in Nairobi City, Kenya

The distribution and sources of organochlorine pesticides (OCPs) in air and surface waters were monitored in Nairobi City using triolein-filled semipermeable membrane devices (SPMDs). The SPMDs were extracted by dialysis using n-hexane, followed by cleanup by adsorption chromatography on silica gel cartridges. Sample analysis was done by GC-ECD and confirmed by GC–MS. Separation of means was achieved by analysis of variance, followed by pair-wise comparison using the t-test (p≤ 0.05). The total OCPs ranged between 0.018 – 1.277 ng/m³ in the air and <LOD – 1391.000 ng/m³ in surface waters. Based on the results, the means of Industrial Area, Dandora and Kibera were not significantly different (p≤ 0.05), but were higher (p≤ 0.05) than those of City square and Ngong’ Forest. The results revealed non-significant (p≤ 0.05) contribution of long-range transport to OCP pollution in Nairobi City. This indicated possible presence of point sources of environmental OCPs in the city. The water-air fugacity ratios indicated that volatilization and deposition played an important role in the spatial distribution of OCPs in Nairobi City. This indicated that contaminated surface waters could be major sources of human exposure to OCPs, through volatilization. The incremental lifetime cancer risks (ILCR) determined from inhalation of atmospheric OCPs were 2.3745  ×  10^?13 – 1.6845  ×  10^?11 (adult) and 5.5404  ×  10^?13 – 3.9306  ×  10^?11 (child) in the order: Dandora > Kibera > Industrial Area > City Square > Ngong’ Forest. However, these were lower than the USEPA acceptable risks, 10^?6 – 10^?4. This study concluded that atmospheric OCPs did not pose significant cancer risks to the residents.     

短期干旱胁迫对马尾松排放挥发性有机物的影响

为探究干旱环境对BVOCs排放的影响,应用动态封闭式采样系统和热脱附-气相色谱-飞行质谱仪,对短期干旱胁迫作用下马尾松的BVOCs排放进行了实验室测量,定量分析BVOCs排放速率和排放组成的变化.结果表明,干旱胁迫时异戊二烯的排放受到抑制,排放速率降低约50%;单萜烯和倍半萜烯的排放水平增强,排放速率分别为137.85和0.98μg/（m²·h）,是未受胁迫时的2.9和2.0倍.除反式-α-香柠檬烯外,干旱胁迫促进各单萜烯和倍半萜烯化合物的排放,是未受胁迫时的1.3~42.4倍,其中3-蒈烯排放的响应最敏感,α-葑烯、α-水芹烯和石竹烯的响应最弱.干旱胁迫时单萜烯和倍半萜烯的排放组成有所变化,但主导的化合物种类不变,单萜烯以α-蒎烯、香桧烯和β-蒎烯为主,占比分别为48%、17%和17%;倍半萜烯以石竹烯和长叶烯为主,占比分别为57%和34%.     

Mesoporous WO3-graphene photocatalyst for photocatalytic degradation of Methylene Blue dye under visible light illumination

Advanced oxidation technologies are a friendly environmental approach for the remediation of industrial wastewaters. Here, one pot synthesis of mesoporous WO_3 and WO_3-graphene oxide(GO) nanocomposites has been performed through the sol–gel method. Then, platinum(Pt) nanoparticles were deposited onto the WO_3 and WO_3-GO nanocomposite through photochemical reduction to produce mesoporous Pt/WO_3 and Pt/WO_3-GO nanocomposites. X-ray diffraction(XRD) findings exhibit a formation of monoclinic and triclinic WO_3 phases. Transmission Electron Microscope(TEM) images of Pt/WO_3-GO nanocomposites exhibited that WO_3 nanoparticles are obviously agglomerated and the particle sizes of Pt and WO_3 are ~ 10 nm and 20–50 nm, respectively. The mesoporous Pt/WO_3 and Pt/WO_3-GO nanocomposites were assessed for photocatalytic degradation of Methylene Blue(MB) as a probe molecule under visible light illumination.The findings showed that mesoporous Pt/WO_3, WO_3-GO and Pt/WO_3-GO nanocomposites exhibited much higher photocatalytic efficiencies than the pure WO_3. The photodegradation rates by mesoporous Pt/WO_3-GO nanocomposites are 3, 2 and 1.15 times greater than those by mesoporous WO_3, WO_3-GO, and Pt/WO_3, respectively. The key factors of the enhanced photocatalytic performance of Pt/WO_3-GO nanocomposites could be explained by the highly freedom electron transfer through the synergetic effect between WO_3 and GO sheets, in addition to the Pt nanoparticles that act as active sites for O2 reduction, which suppresses the electron hole pair recombination in the Pt/WO_3-GO nanocomposites.