A new liquid membrane, mercury(II) ion-selective electrode (ISE) based on 1,3-diphenylthiourea as a neutral carrier was developed. In solubility tests of 1,3-diphenylthiourea in six different plastizicers, tris(2-ethylhexyl) phosphate (TEHP) showed the best performance and was selected for the membrane. Several ISEs were conditioned and tested for the selection of seven metal ions (Hg²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Mg²⁺ and Ag⁺). The best Nernstian response was obtained for Hg²⁺ with an experimental slope of 58.6 ± 0.8 mV per decade in the concentration range 6.0 × 10⁻⁶–5.0 × 10⁻⁴ mol l⁻¹; the presence of the complex Hg(OH)⁺ ion explains the slope of the response curve. The ISE showed stable detection reproducibility during 6 weeks, with a practical detection limit of 10⁻⁶ mol dm⁻³ and a high selectivity for Cd²⁺, Pb²⁺, Co²⁺, Cu²⁺, Sr²⁺, Zn²⁺, Ca²⁺, Mg²⁺, Mn²⁺, K⁺, Na⁺ and NH₄ ⁺ ions. Only one interference for Ag⁺ was found. A second linear response curve for Hg²⁺ was obtained at pH 4 with a slope of 30.8 mV per decade in the concentration range 2.0 × 10⁻⁶–2.1 × 10⁻⁴ mol l⁻¹.

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.

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.