Elements in crops: Their role in agriculture, their nutritional value, the reasons for concern for human health

Globalization has created both opportunities and challenges for food producers in the interconnected world of the 21st century [1]. The international exchange of food supplies has given consumers greater choice and access to food products throughout the year, while providing producers with more business opportunities [2]. However, the distribution of food resources remains a critical issue. Similarly, monitoring product safety and maintaining high quality standards is difficult due to differences in food safety regulations [3]. Finally, the high production and waste of food resources have made the system unsustainable [4]. Therefore, ensuring sustainability and food quality are two of the most important challenges for the future of the food industry [2,5]. Consumer preferences indicate that food should be sustainable and come from a circular economy with a low environmental impact [6]. Additionally, food should also be of high quality and nutritional value, while being safe and free of toxic substances [2,7]. Finally, traceability and authenticity also provide added value for consumers [8]. The challenges therefore include the development of new sustainable production methods and analytical methods for quality control, safety, traceability, and authenticity. In this context, the monitoring of elements in crops is crucial. Although over 95% of the plant's biomass consists of only four main elements - carbon, hydrogen, oxygen, and nitrogen - other macroelements such as calcium, chlorine, potassium, magnesium, sodium, phosphorus, and sulfur [9] are also essential for plant metabolic processes. At lower concentration levels, trace or ultratrace elements play a physiological role in plant, animal, and human nutrition. Their imbalance can cause issues in plant growth and yield, as well as human health. Some elements have no physiological role in plants and can be toxic even in small amounts. Maximizing yield, safety, and quality of plant productions requires optimal concentrations of main elements in crops. However, some cultivation practices, such an inappropriate use of fertilizers [10] or risky soil amendments [11], may conflict with sustainability and lead to a disregard of nutritional and toxicological aspects related to elements. Therefore, it is important to monitor trace element levels in crops to ensure the health of both plants and consumers. Trace elements play several roles in many biological processes [9,12]. Iron, zinc, copper, selenium, iodine, manganese, molybdenum, and fluorine [13,14] are key mineral nutrients for both plants and animal physiology. The four most harmful toxic elements are arsenic, cadmium, mercury, and lead [15]. The impact of these elements on biotic communities depends on their concentration, duration of exposure, and the physiology of the plant or target organism. Toxicity can vary depending on the chemical form, especially for elements like arsenic, cadmium, mercury, and chromium [16]. Crops can become polluted both through human activities, such as the contamination of rice with cadmium [17,18] or natural routes, like for arsenic [18,19]. Toxic elements can accumulate in the edible parts of plants, exceeding safety thresholds set by international food safety organizations [20,21]. Other elements do not have known physiological functions or their toxicity has not been determined. Rubidium, strontium, and rare earth elements show significant variability in their levels, often related to the environment. Traceability and authenticity studies find these elements noteworthy [22]. Quantifying minority and trace elements, as well as toxic elements, can authenticate or add value to plant-based products [23]. The articles in this special issue should increase knowledge about the role of elements in agricultural production for sustainability, crop improvement, and food safety. Additionally, contributions aimed at ascertaining the quality or authenticity of crops using their elemental fingerprint are strongly encouraged.