Here, a mathematical model is presented, which accounts for the dependence of the surface electrical charge density (σ) on pH and the concentration of added salts (C s), generated when a water drop rolls or slides on the surface of a hydrophobic polymer, a process known as liquid–polymer contact electrification (LPCE). The same model was successfully applied to fit the isotherms of ξ-potential as a function of pH, reported in the literature by other authors for water–poly­(tetrafluoroethylene) (PTFE) interfaces. Hence, the dependence of σ and ξ on pH was described using the same concept: acid–base equilibria at the water–polymer interface. Equilibrium constants were estimated by fitting experimental isotherms. The experimental results and the model are consistent with a number of 10–100 acid–base sites/μm2. The model predicts the increase of |σ| and |ξ| with pH in the range of 2–10 and the existence of a zero-charge point at pHzcp ≅ 3 for PTFE (independent of C s). Excellent fits were obtained with K a/K b ∼ 9 × 107, where K a and K b are the respective acid and base equilibrium constants. On the other hand, the observed decrease in |σ| and |ξ| with C s at fixed pH is quantitatively described by introducing an activity factor associated with the quenching of water activity by the salt ions at the polymer–water interface, with quenching constant K q. Additionally, the quenching predicts a decrease in |σ| and |ξ| at extreme pH, where I > (1/K q) (I: ionic strength), in agreement with literature reports.

Water drops become charged after sliding on a polymer surface. The variation of the detected charge with pH and ionic strength are compatible with OH− or H+ transfer from the drop to the polymer. These changes are accounted for by a thermodynamic model.

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Lead is known to be a highly toxic metal; it is often found in soils with the potential to be incorporated by plants. Here, the bioaccumulation of lead by rapeseed (Brassica napus) from a soil with Pb(II) added just before sowing is studied. The effect on plant organs is also studied at the ontogenetic stages of flowering and physiological maturity. Moreover, the chemical fractionation of Pb in the rhizosphere and bulk soil portions is investigated and related to Pb accumulation in plant organs. B. napus are found to accumulate Pb in its organs: 1.5-19.6 mg kg −1 in roots, 3.3-15.6 mg kg −1 in stems, 0.5-8.6 mg kg −1 in leaves in all treatments, and in grains 1.45 mg kg −1 at physiological maturity and only for the highest Pb dose (200 mg kg −1 ). Plant biomass reduction was observed to be about 20% at the flowering stage and only for the highest Pb dose. The analysis of metal fractionation in soil shows Pb migration from the bulk soil to the rhizosphere, attributed to concentration gradients created by root intake. Along the time period studied, lead chemical fractionation in soil evolved toward the most stable fractions, which coupled to plant uptake depleted the soluble/ exchangeable one (assumed bioavailable).

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