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Three quarters of the world's significant urban centers are located in coastal regions where clay minerals are prevalent. The microstructures and physico-mechanical properties of clay sediments are highly susceptible to alterations in pore water chemistry. The pore water chemistry in soil changes easily due to groundwater pollution, seawater erosion, degradation, etc. However, there are several inconsistencies in the literature on the change of physical and mechanical properties of clay soils caused by the change of pore water chemical properties, i.e., disparate experimental results were reported for the same soil property, or varying explanations were proposed for the identical experimental results. Currently, the research in this field mainly focuses on the macroscopic behavioral modifications while lacking the explanations of microscopic mechanism. Therefore, this paper presents a comprehensive review of researches conducted over the past four decades on the impact of pore water chemistry (including salt type, salinity, ion valence, pH) on soil properties such as the microstructure, settlement, Atterberg limits, shear strength, conductivity, unsaturated soil mechanics properties and thermal properties. The fundamental mechanisms underlying the varied experimental observations on clay sediments affected by salt and pH are systematically explored, and deficiencies in this field are identified. The observed dispersion in the literatures is attributed to the spatial variation and heterogeneity of soil compositions, different test methods, and insufficiency of the fundamental microscopic mechanisms of the observed soil behaviors, etc. Therefore, it is necessary to further explore the essential mechanisms of the test results in the future to establish a unified conclusion. [ABSTRACT FROM AUTHOR]

The content of heavy metals in water and soil is a key parameter for evaluating the geochemical vulnerability of an ecosystem. These elements display a limited solubility and are easily trapped and adsorbed by phyllosilicate minerals; they are thus preferentially partitioned in the fine fraction of sediments. In this light, an analysis of recent river sediments gives information on possible water pollution, and more in general on the related ecosystem. We therefore investigated the chemical–mineralogical features of clay sediments outcropping around the town of Ferrara, paying particular attention to their fine fraction (grain size<2 μm).X-ray fluorescence (XRF) analyses indicate that the abundance of transition trace elements, such as Cr and Ni, is positively correlated with MgO wt.%, and discriminates two well-delineated populations of samples, respectively characterised by high (Cr>180 ppm; Ni>100 ppm) and low (Cr<180 ppm; Ni<100 ppm) contents of these elements. The mineralogical composition of the fine fraction (<2 μm) was investigated through X-ray powder diffraction (XRPD) integrated with differential thermal (DTA) and thermogravimetric analyses (DTG), showing that: low-Cr samples are characterised by a higher proportion of clay minerals in which smectite+mixed layers are more abundant than chlorite (Sm+ML/Chl>1); on the other hand, the high-Cr samples have a coarser grain size, and a lower abundance of clay minerals in which chlorite (Mg-rich chlorite in this group of samples) predominates over smectite+mixed layers (Sm+ML/Chl<1). These two distinct groups of samples are ascribed to different sources: high-Cr lithologies are related to the sedimentary contribution of the Po river, whereas low-Cr sediments plausibly derive from small rivers of Apennine origin (e.g. the Reno river). Within the high-Cr group, concentrations of Ni and Cr tend to be higher than those indicated by the current environmental Italian legislation. However, in the study–case presented here, the detected high heavy-metal concentrations are not related to urban–industrial–agricultural activities, but instead appear to be typical of the original lithologies.An integration of similar scientific contributions would be useful to set up a geochemical–mineralogical database as a first step toward the preparation of more complete thematic maps. These would provide information relative to the behaviour (e.g. distribution and abundance) of chemical elements within the different geochemical spheres, and would be useful for recognising and interpreting possible geochemical anomalies induced by pollution processes. [Copyright &y& Elsevier]