Contamination of natural ecosystems by inorganic and organic pollutants is of growing concern. For environmental remediation, a strategy to improve the sorption capacity of clay minerals for organic compounds, including pesticides, and for inorganic compounds, such as heavy metals, could be the replacement of their inorganic exchangeable cations with organic cations containing specific functional groups with affinity for both types of contaminants. In this work, a Wyoming montmorillonite was treated with four different natural organic cations, L-carnitine, L-cysteine ethyl ester, L-cystine dimethyl ester, and thiamine, which were selectively chosen to increase the hydrophobicity of the clay surface and to supply functional groups with affinity for pollutants. After characterizing the samples by elemental analysis, X-ray diffraction, infrared spectroscopy and specific surface area measurements, we studied the ability of these organoclays to sorb Hg(II) ions and the herbicide simazine from aqueous solution and to enhance the Hg(II) and simazine retention capacity of selected soils. The competitive sorption between the metal ions and the herbicide on selected samples was also investigated. Most of the organic cations enhanced the affinity and the sorption strength of montmorillonite for Hg(II) and simazine. Addition of selected organoclays to different soils resulted in an improvement of the Hg(II) and simazine retention capacity of the soils, although this effect was dependent of soil type. In general, little competition between the heavy metal ion and the herbicide for sorption on the organoclays was observed. The results demonstrated that specific modification of smectitic clay minerals with natural organic cations containing appropriate functional groups can be a useful strategy to improve the performance of organoclays for the simultaneous removal of inorganic and organic species from the environment.