# Application of the _Aliium_ Test in Toxicity Studies of Lead and Copper: A Cytological Perspective
## 1 Introduction  
Heavy metal pollution contributes to the deterioration of human health by increasing mortality and reducing life expectancy [1, 2]. Non-biodegradability represents a biological threat due to its adverse effects on cellular integrity and metabolic processes. An estimated 47,000 people die every year from heavy metal pollution in Poland, the European county with the third highest levels of air pollution, after Bulgaria and Cyprus [3]. In the agricultural ecosystem, excess heavy metals in the soil severely affect the health of crop plants, compromising their yield and quality [4, 5, 6, 7]. Since even small concentrations of heavy metals can determine metabolic modifications, the maximum allowable limits areof great importance to public health [8]. Heavy metals binding to functional groups of enzymatic proteins, such as sulfhydryl (-SH) groups [9], inhibit essential processes such as glycolysis and the Krebs cycle [10]. Also, the impact of heavy metals depends greatly on the genotypes, the stage of development, and age [11; 12; 13]. The primary pathway through which plants accumulate heavy metals is through root absorption from the soil [14; 15; 16]. Since heavy metals are non-biodegradable, they can accumulate in plants, which can subsequently be consumed, posing a significant risk to human health [17]. The effect in plants is reflected in physiological processes such as photosynthesis [18], nutrients absorption [19], and root system development by accumulation in the plant's tissues. Furthermore, cellular functions such as cell division are effected [20], leading to morphological deformation and a dramatic increase in the induction of programmed cell death (PCD) [21; 22]. Cellular damage resulting from heavy metals is primarily caused by the generation of reactive oxygen species (ROS). In plants, ROS production has also been demonstrated under the impact of drought and salinity. ROS are molecules containing oxygen atoms with unpaired electrons, formed as byproducts of incomplete decomposition processes [23]. The effect on the mitotic index (MI) and the significant increase in the abnormalities index (AI) correlate with ROS production, as both have been demonstrated in several studies involving heavy metals [23]. The presence of heavy metals in soil not only influences or reduces crop production but also affects water quality, exacerbates the effects of climate change, and poses significant threats to human health [24; 25]. According to reports on soil contamination, approximately 70% of heavy metal pollution is attributed to industrial and mining activities [26]. The most common heavy metals are represented by copper (\(Cu^{+2}\)) and lead (\(Pb^{+2}\)). \(Cu^{+2}\) and \(Pb^{+2}\) rank among the most significant and frequently associated soil contamits, posing a serious concern for the health of the plants and the ecosystems [27; 28]. Lead (\(Pb^{+2}\)), a heavy metal non-essential to the organism, continues to be widely used in numerous industrial processes and is found as a contaminant in all environmental compartments [29]. \(Pb^{+2}\) absorbed by roots becomes bound to the carboxyl groups of uronic acid mucilage or directly to the polysaccharides on the surface of rhizodermal cells [30]. Once adsorbed on the rhizodermal surface of roots, lead can passively enter the roots through water transport pathways [31]. One study found that the highest concentrations are found in the root tips, where the cells are young and have thin cell walls [32]. According to studies, \(Pb^{+2}\) is typically found in soil at normal concentrations ranging from 10-40 mg/kg (\(\equiv\)0.048-0.193 mM). The legislative limits for lead (\(Pb^{+2}\)) across individual EU countries vary widely, ranging from 45 to 1200 mg/kg DM (\(\equiv\)0.217-5.792 mM) [33; 34; 35]. Copper (\(Cu^{+2}\)), a metal essential for the body, is required for the organism's metabolic processes in the range of 1.4 to 2 mg per kilogram of body weight [36].