No abstract

This study is aimed at assessing atmospheric deposition of heavy metals using the epiphytic moss genera Fabronia ciliaris collected from six urban sites in the Metropolitan Zone of the Toluca Valley in Mexico. The concentrations of K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, and Pb were determined by total reflection X-ray fluorescence technique. Results show that the average metal concentration decrease in the following order: Fe (8207 mg/Kg) > Ca (7315 mg/Kg) > K (3842 mg/Kg) > Ti (387 mg/Kg) > Mn, Zn (191 mg/Kg) > Sr (71 mg/Kg) > Pb (59 mg/Kg) > Cu, V (32 mg/Kg) > Cr (24 mg/Kg) > Rb (13 mg/Kg) > Ni (10 mg/Kg). Enrichment factors show a high enrichment for Cr, Cu, Zn, and Pb which provides an evidence of anthropogenic impact in the industrial and urban areas, mainly due to the intense vehicular traffic and the fossil fuel combustion. Monitoring techniques in mosses have proved to be a powerful tool for determining the deposition of heavy metals coming from diverse point sources of pollution.

The metropolitan area of the Toluca Valley (MATV) extends over an area of 1208.55 km2 and has 1,361,500 inhabitants making it the fifth highest populated area in the country and the second highest in the state. The MATV has several environmental problems, with regards to the air quality. Particles PM10 and PM2.5 are considered to be the main pollutant due to these particles frequently exceeding the limit laid down in the standards of the air quality in the country. For this reason, samples of the mosses Fabriona ciliaris and Leskea angustata were collected at different sites in MATV, Mexico in order to establish the atmospheric deposition of heavy metals by means of the analysis of the mosses tissues. Results show the average metal concentrations in the mosses in the order of: Zn > Pb > Cr > Cd. The concentration capacities of heavy metals were higher in Fabriona ciliaris than Leskea angustata. Enrichment factors for Cr, Zn, Pb and Cd were obtained using the soils from the same sampling area. Enrichment factors results show that Cr is conservative in both sampling seasons with a terrigenous origin; Zn is moderately enriched in both sampling seasons and mainly associated to pedological-soil or substrate contribution and anthropogenic activities and Cd is highly enriched in the rainy season and Pb is highly enriched in both sampling seasons, with a predominantly anthropogenic origin. This study provides information to be considered in the strategies for similar environmental problems in the world.

Scanning electron microscopy (SEM) and energy dispersive atomic X-ray spectrometry (EDAX) were used to study the response mechanism of a previously reported new Hg membrane ion-selective electrode (ISE) based on 1,3-diphenylthiourea. These techniques allowed the study of the membrane surface characteristics, such as the morphological homogeneity and chemical composition. A 'twice Nernstian' response at pH > or = 7 was explained by the detection of the Hg(OH)+ cation. A normal Nernstian response was found at acidic pH values. Using these techniques, both coordination compounds, [Ligand-Hg-OH] at pH 7 and [Ligand-Hg-Ligand] at pH 4.5, were confirmed on the electrode membrane surface activated with Hg(NO3)2 solution at both pH values. These methods provide results which are independent of the potential measurement data and in agreement with them. A successful response model has explained both independent and unbiased sets of results. These conclusions confirm the proposed response mechanisms for this new Hg membrane sensor.

Triclosan (TCS) adsorption behavior by a modified zeolite with Cetyl Trimethyl Ammonium Bromide (CTAB) was evaluated factoring in pH, contact time, and TCS initial concentration in a batch system. Natural clinoptilolite-type zeolite from Sonora, Mexico was conditioned with a sodium chloride solution, and, subsequently, modified with CTAB. All the zeolites were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS), and the Zero Point Charge (pHZPC). It was found that the morphological and structural properties of natural zeolite were not affected after treatment with cationic surfactant. Furthermore, adsorption process efficiency was enhanced by the presence of CTAB, obtaining TCS maximum adsorption capacity at an optimal pH of 9.0. In this context, the positively charged surface of the modified zeolite and the anionic triclosan species present were decisive. Kinetics data were well adjusted to a pseudo-second order model with a TCS adsorption capacity of 1.430 ± 0.051 mg g-1 at an equilibrium time of 18 h. Isotherm results were best adjusted to the Langmuir model with a qmax = 2.027 mg g-1 using an initial Co concentration of 18.0 mg L-1, and reaching an equilibrium Ce concentration of 0.559 mg L-1. The mechanism for the adsorption of TCS by CTAB-modified zeolite was proposed to be electrostatic attractions between the group of partial positive charge of CTAB and the anionic species of triclosan. Consequently, CTAB-modified zeolites could be used as effective adsorbents for triclosan removal.