# Potential Metal Contamination in Foods of Animal Origin--Food Safety Aspects
## 2 Major Toxic Metals in Food  
### Arsenic (As)  
The trivalent arsenite (As\({}^{3+}\)) form of arsenic is increasing day by day in soil and water, causing loss to crop productivity. Its presence in the soil and irrigation water in a higher concentration exceeding the permissible limit has become a threat to crop production and human livelihood. In plants, the uptake of As\({}^{3+}\) is affected by oxidizing or reducing the environment of the soil, and the pH and is mediated by various transporters such as Nodulin-26-like aquaporins (such as Lsi1 and Lsi2). The phytotoxic behavior of As\({}^{3+}\) severely affects the growth and development of crop plants, which not only reduces productivity but also consecutively affects human lives. Deposition of As\({}^{3+}\) in staple food crops allows direct As exposure, affecting around 80% of the world population [9]. The concentration of As in plants is usually less than 1.0 mg/kg dry weight (d.w.). Besides the physical-chemical properties and the chemical speciation of As in growth medium, As uptake by plants is also controlled by various physiological/tolerance mechanisms taking place in different tissues of plants under As stress [10]. In aquatic environments, the arsenic content of algae is in the range 1-180 mg/kg, in marine fish and bivalves it is <2-170 mg/kg, and in freshwater fish it is <0.1-3 mg/kg [11]. However, organic arsenic compounds (e.g., arsenic betaine, arsenic sugar) found in these foods are generally non-toxic. Arsenicals can cause oxidative stress and affect biotransformation methylation processes and the metabolism of other essential metals. Thus, based on these processes, it is classified as a carcinogenic compound [12; 13; 14; 15]. Arsenates can replace phosphate compounds in various biochemical reactions due to their similar structure and properties, thus uncoupling oxidative phosphorylation and reducing the amount of ATP. Trivalent arsenic derivatives (e.g., arsenites) bind to thiol and sulfhydryl groups of enzymes, receptors, and coenzymes, inhibiting their physiological function [12; 14]. Arsenite, arsenate, dimethyl arsenate, and monomethyl arsenate can induce developmental abnormalities, perinatal death, and growth retardation in hamsters, mice, and rats [16]. Absorption of inorganic arsenate and arsenite compounds from aqueous solutions is substantial (<90%) in humans. Absorption of inorganic compounds from food is lower (60-75%) [17]. Monomethyl-arsonate has been detected in human urine following the ingestion of large amounts of inorganic arsenic compounds [18]. [PERSON] et al. detected nearly 12 arsenic metabolites in human urine following the ingestion of synthetic arsenic sugar [19]. The proportion of arsenic compounds excreted in urine is generally 20% inorganic, 15% monomethyl-arsonate, and 65% dimethylarsonate in humans [20]. The ratio depends on the type of foods ingested and the types of arsenicals found in them. In the urine of Japanese university students who consumed large amounts of marine fish and shellfish and thus ingested organic arsenic compounds (e.g., arsenic betaine), 9.4% inorganic, 3.0% monomethyl-arsonate, and 58.2% trimethyl-arsenate were measured [21]. Less than 90% of orally ingested organic arsenic compounds (e.g., Na-p-N- glyco-larsenylate) are excreted in the feces within 3 days, with only about 4-5% appearing in the urine [22]. Aquatic organisms (fish, shellfish, squids) can contain relatively high levels of arsenic, but the majority (about 95%) is found as organic derivatives (arsenocholine, arsenobetain, arsenosugars). Their toxicity is lower, and they are quickly excreted from the human body. Generally, the remaining 5% of arsenicals are inorganic, with potential toxic effects [11; 23; 24; 25].