Este artículo presenta una revisión de algunas características toxicológicas de metales pesados, sus fuentes industriales, los niveles permisivos de vertimiento y 20 diferentes técnicas subdivididas en convencionales y no convencionales empleadas para la remoción de metales pesados en medios hídricos, así como las condiciones fisicoquímicas en las que estos tratamientos han presentado mejores eficiencias de remoción.

The equilibrium solubility at temperatures from (293.15 to 313.15) K, dissolution thermodynamics and preferential solvation of sulphadiazine (SD) in {acetonitrile (ACN) (1) + water (2)} mixtures is reported. Mole fraction solubility of SD (x₃) increases when temperature arises and also increases with the ACN proportion increasing. It varies from 4.81 × 10^–6 in neat water to 6.02 × 10^–4 in neat ACN at 298.15 K. Solubility behaviour was adequately correlated by Jouyban-Acree, modified Wilson and non-linear (proposed by Machatha et al.) models and the obtained mean percentage deviations (MPD) are 4.1%, 2.3% and 2.3%, respectively. The comparison of the MPD shows that the prediction using Jouyban-Acree model is more accurate than Jouyban-Acree-Abraham equation for solubility prediction of SD in {ACN (1) + water (2)}. From the variation of solubility with temperature the apparent thermodynamic analysis of dissolution was performed in all the mixtures and neat solvents. Based on the inverse Kirkwood-Buff integrals preferential solvation parameters were calculated. SD is preferentially solvated by water in water-rich mixtures (0.00 < x₁ < 0.26) but preferentially solvated by ACN in the interval (0.26 < x₁ < 0.65). In ACN-rich mixtures the behaviour is not well defined.

The solubility of methylparaben was determined in acetonitrile + water mixtures at several temperatures (278.15 K to 318.15 K). The solubility curves as a function of acetonitrile ratio showed a maximum at a mass fraction of acetonitrile 0.85 at all temperatures. In all cases, the homogeneous mixture splits into two liquid immiscible phases. The concentration range at which phase separation takes place is 0.35–0.70 in a mass fraction of acetonitrile, showing a clearer separation at higher study temperatures. According to the results of DSC, this phase separation was not related to solid phase changes (polymorphism). The apparent enthalpy of the solution process was a nonlinear function of the acetonitrile ratio, and the solution process of the drug is endothermic and enthalpy determined. Finally, the enthalpy-entropy compensation analysis shows a non-linear behaviour, possibly due to the influence of acetonitrile in the solution process of methylparaben in cosolvent acetonitrile + water mixtures.

Solubility is one of the most important physicochemical properties due to its involvement in physiological (bioavailability), industrial (design) and environmental (biotoxicity) processes, and in this regard, cosolvency is one of the best strategies to increase the solubility of poorly soluble drugs in aqueous systems. Thus, the aim of this research is to thermodynamically evaluate the dissolution process of triclocarban (TCC) in cosolvent mixtures of {N-methyl-2-pyrrolidone (NMP) + water (W)} at seven temperatures (288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K). Solubility is determined by UV/vis spectrophotometry using the flask-shaking method. The dissolution process of the TCC is endothermic and strongly dependent on the cosolvent composition, achieving the minimum solubility in pure water and the maximum solubility in NMP. The activity coefficient decreases from pure water to NMP, reaching values less than one, demonstrating the excellent positive cosolvent effect of NMP, which is corroborated by the negative values of the Gibbs energy of transfer. In general terms, the dissolution process is endothermic, and the increase in TCC solubility may be due to the affinity of TCC with NMP, in addition to the water de-structuring capacity of NMP generating a higher number of free water molecules.