## 1 Introduction  
Tungsten (W) is a metal characterized by a very low abundance in the Earth's crust, and thus occurs in soils in small concentrations of less than 3 mg kg\({}^{-1}\)[1]. Tungsten occurs naturally in several minerals such as wolframite (Fe,Mn)WO\({}_{4}\), hubnerite MnWO\({}_{4}\), ferberite FeWO\({}_{4}\), and scheelite (CaWO\({}_{4}\)). It is used in a variety of industrial activities for the production of high-tech components [2] due to its high melting point and resistance to corrosion. Tungsten has also been used in several military applications as a substitute for the dangerous depleted uranium [1; 3]. The most important use of tungsten is in the production of tungsten/nylon bullets as alternatives to lead-based munitions [4]. Soils are an important sink and source of tungsten in the environment as a result of the transport of dust deriving from erosion processes. These last have been recognized as one of the most important contributions to the dispersion of tungsten into the environment [1]. In soil, tungstate is the most stable form of the element. This oxyanion is chemically similar to molybdate, however, while molybdenum is an essential element [5], tungsten is not an essential micronutrient, and it has been historically regarded as inert in the soil environment and classified as nontoxic for human health [6]. However, several ecotoxicological studies have discovered that under certain environmental conditions, tungsten compounds can be solubilized and enter the biogeochemical cycles [7; 8]. Occupational studies on workers' exposure in industry where tungsten is used have revealed several adverse health effects [9]. The presence of tungsten in the atmosphere has been particularly studied in Nevada, due to the possible link between tungsten in the atmosphere and cases of childhood leukemia [10; 11]. Knowledge regarding the effects of tungsten in the soil, on its transfer in the food chain, and thus on human health is still incomplete [1]. In some cases, tungsten has been found to be nontoxic and substantially inert in the soil [12], whereas in other studies, very negative hypotheses have been put forward on the possible action of tungsten in the formation of neoplasms in animal cells [7]. The growing interest in this element is further highlighted by several studies on the impact of W on soil microorganisms. Several works have shown that under certain conditions, the presence of tungsten increases the microbial biomass [13]. Conversely, in other cases, negative impacts on microbial activity have been verified [14]. The increase in the industrial and military use of tungsten has become of interest due to its potential entry into the food chain following uptake by agricultural crops. Moreover, in agricultural soils tungsten is also added to fertilizers [15], and may be present in sewage sludge due to its presence in many household products [16]. Many plants such as oats, radiishes, and lettuce are able to grow in soil with high tungsten concentrations [17] and can accumulate significant quantities of the metal also due to its similarity with molybdenum [14]. At high concentrations, tungsten has been reported to decrease root elongation in _Pisum sativum_ and _Gossypium hirsutum_[18; 19; 20]. High concentrations of tungsten in plants have been reported for species growing on the soils of abandoned mine [21; 22; 23]. Near tungsten mines, its transfer from soil to rice has been reported as a possible health risk via the food chain [24]. In general, the tungsten content in roots is higher than that in the aerial parts of plants [25; 26]. Studies on tungsten are very lacking in Italy where the potential problems arising from this element are completely neglected. This element is not taken into consideration in any environmental legislation, nor in the regulations that define the quality of fertilizers to be used in agriculture. It therefore seems no longer unpostponable to study the behavior of this element in Italian soils with a view to protecting the environment and human health.