In this work, adsorption feasibility of a cationic dye, methylene blue (MB), onto an anionic hydrogel nanocomposite was investigated in detail. Firstly, the hydrogel nanocomposite was synthesized via a simple solution copolymerization of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid monomers in the presence of montmorillonite (MMT) by using ammonium persulfate as an initiator and methylene bisacrylamide as a crosslinker. Then, the effects of agitation time, MMT content, pH, initial dye concentration, adsorbent dose, and temperature were optimized with respect to the dye adsorption capacity of nanocomposites. The thermodynamic parameters such as changes in standard free energy, enthalpy, and entropy demonstrated that dye adsorption onto the hydrogel nanocomposite was spontaneous and endothermic, and especially more effective at high temperatures. Moreover, the results indicated that the equilibrium adsorption isotherm data of the hydrogel nanocomposite better fit to the Redlich-Peterson than to the Langmuir, Freundlich, and Temkin models. The experimental results also fit to pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models. The results indicated that the adsorption of MB followed pseudo-second-order kinetics.
We evaluated 2,4-dichlorophenoxyacetic acid (2,4-D) exposure in four municipalities with and without cosmetic pesticide bylaws in British Columbia, Canada. We recruited a child (aged 1.5-5 years) and adult from 10 households in each city, who provided urine samples in May and June, 2009. No households had used pesticides for 7 days prior to sample collection. We quantified urinary 2,4-D using LC/MS/MS. Quantities of 2,4-D in urine were similar across cities and below biomonitoring equivalents corresponding to references doses in the United State of America and Canada. When adult's and children's urines were analyzed together in linear mixed-effects regression models, natural log urinary 2,4-D was significantly associated with having a diet of ⩾50% organic food (β=-0.6 (0.3) μg/l, P=0.05). Without natural log transformation, median concentration of urinary 2,4-D among those who ate ⩾50% organic food (n=12) was 1.4 μg/l versus 1.5 μg/l for others (n=59). Lack of a significant association (two-sided alpha=0.05) between pesticide bylaws and urinary 2,4-D might reflect small sample size, lack of recent acute exposure, or that 2,4-D exposure is primarily influenced by sources of exposure not addressed through bylaws. Food might be a route of exposure to 2,4-D, consistent with other studies. Future research will require larger sample sizes for sufficient statistical power.
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