I contaminanti inorganici nel riso italiano: stato dell’arte e prospettive

[Autom. eng. transl.] Traditional rice cultivation in submerged soils substantially modifies the biogeochemical cycle and the availability of nutrients and contaminants in the soil. Among the most critical inorganic contaminants for rice production are inorganic arsenic (AS) and cadmium (Cd), whose concentration thresholds in the grain have been regulated for several years. Recently, the growing attention to consumer health has led to a review of the admissible thresholds that have decreased, in white rice, from 0.20 to 0.15 mg/kg. Furthermore, the introduction of a threshold for total nickel (Ni) is imminent. The need to produce increasingly higher quality rice, while maintaining the environmental and economic sustainability of the crop in a context of climate change, represents a major challenge for Italian rice cultivation. The adaptations of agronomic practices to the needs of a rational use of water resources, as well as the introduction of conservative and regenerative agriculture practices, certainly impact the phytoavailability of contaminants, but not all the mechanisms that regulate the variations in the dynamics of these elements have been clarified. In the international literature, most of the studies concern soil environments and varieties different from the Italian ones, making the information difficult or only partially transferable to the Italian reality. For this reason, for several years, a working group that unites the Ente Nazionale Risi, the University of Turin and the Catholic University of Piacenza has been studying the transfer of inorganic contaminants from soils to rice produced in Italy. The mechanisms that regulate the mobility in the soil and the uptake of As and Cd by the rice plant have been at least partially clarified, and it has been possible to provide some indications to rice growers to reduce their concentration in the grain. The behavior of Ni in the soil-water-plant system in rice fields is still little known and the experimental observations collected so far are more difficult to interpret. This contribution aims to present a broad overview of the research carried out over the years in this regard, exposing the dynamics that regulate the soil-plant transfer and the results of the interventions tested to limit the accumulation of As and Cd. The mechanisms that condition the mobility of Ni in soils subject to periodic submersion will also be presented together with some preliminary data from the research program underway on this element.