Applied Sciences  
Special Issue on Potentially Toxic Trace Elements in Contaminated Sites: Fate, Risk and Remediation  
[PERSON] 1,* [PERSON] 2 and [PERSON] 3\({}^{\text{\textregistered}}\)  
The occurrence of potentially toxic elements (PTEs, including As, Cd, Hg and Pb) of both anthropogenic and natural origin in the environment represents an issue of global concern, leading to a general decline in environmental quality in both continental and aquatic systems. These contaminants are easily accumulated in soil and sediment compartments, which may represent both a sink and a potential secondary source of contamination. Indeed, physical and biogeochemical processes may promote the release and mobility of bioavailable forms of PTEs, affecting water quality, biota and human health. Relevant investigations focused on PTE sources, mobility, and fate are extremely important for assessing the geochemical status of the environment, and for providing valuable mitigation and management strategies for contaminated sites. This Special Issue aims to examine the occurrence, distribution, and fate of PTEs of both natural and anthropogenic origin in the environment, as well as management and remediation approaches to assess and mitigate potential ecological and health risks. Six research articles have been collected, and focus on PTE occurrence, mobility, and fate in both continental and aquatic systems, along with the risk assessment, management and potential remediation strategies of PTE-contaminated sites. [PERSON] et al. (2013) investigated the distribution of As in several environmental matrices (soil, groundwater and vegetables) in a densely populated area of Versilia (Tuscany, Italy). The region is characterized by rich mineralization, and falls within an abandoned mining area once exploited for pyrite extraction and now feeding a natural stream catchment, with acid drainages highly contaminated by PTEs, including As. The investigation consists of a risk analysis for both adults and children, and based on surface soil ingestion, dermal contact and soil dust inhalation, as well as exposure through the consumption of vegetables. The authors found that although As concentrations in soil are below the threshold imposed by Italian regulations, health risk assessments indicate that direct exposure to soil is a potential harmful exposure route to As. Arsenic (As), as a priority PTE, is also the focus of the study of [PERSON] et al. (2013). Here, As encapsulation into plant phytoliths (silicon deposits within the cell walls of the plant endodermis and epidermis) was investigated, as it could represent an efficient mechanism for reducing As translocation, at the same time stimulating the plant's antioxidant system. To improve the current knowledge regarding this mechanism, the authors selected two phytolith accumulators (_Pteris multifida_ and _Pteris australis_) and compared their behavior for different soil water contents. The high As content in the phytoliths of _P. multifida_, which increased with soil water content, suggests that this plant may play as the role of a hyperaccumulator, thus affecting the fate of As in soil. The occurrence of PTEs as nanoparticles in the environment was addressed by [PERSON] et al. (2013), who studied the capacity of biochar to retain CeO\({}_{2}\) nanoparticles (CeO\({}_{2}\)NPs) in soil. The authors hypothesized that the quenching process at the end of pyrolysis might influence the effects of biochar on the nanoparticles' mobility. As quenching with water results in biochar having a higher porosity, in this study, CeO\({}_{2}\)NPs leaching from a soil amended with two biochars, obtained after dry and wet quenching, respectively, was evaluated. The authors found that the biochar had an effect on the amount of the mobile fraction of CeO\({}_{2}\)NPs, and that dry quenching can reduce CeO\({}_{2}\)NP leaching.