# Illegal Nitrite Treatment of Red Tuna and Prolonged Storage: What About Other Food Safety Risks?
## 1 Introduction  
Proposed in all diets because of their high nutritional properties, seafood products have seen a marked increase in demand and consumption in recent years. The EFSA [1] and WHO [2] recommend consumption of one to two fish-based meals per week as fish is essential for a complete diet due to its high content of proteins, free amino acids, and other health-enhancing components such as vitamins, minerals, and omega-3 fatty acids [3]. Among fish products, the tuna supply chain is particularly market-driven by the increasing demand for processed/ready-to-cook tuna products. World tuna consumption is estimated at 0.45 kg per capita per year, which represents 2.2% of global fish consumption [4]. At the same time, tuna fish meat is a highly perishable foodstuff and easily subjected to microbial growth and decomposition. The fresh meat has a brightred color which quickly turns to brown during storage due to the autoxidation of myoglobin to metmyoglobin. In order to extend or even enhance the attractive aspect of fresh red tuna meat, different strategies were proposed to stabilize the red color, such as gassing with carbon monoxide (CO) or the addition of nitrate and/or nitrite salts and also by adding vegetable extracts with high nitrate concentration and in combination with reducing agents (ascorbic acid) to form nitric oxide (NO), which binds as a ligand to myoglobin. CO complexes are reported to be cherry red, while NO-complexes are described as pink red [5; 6]. These procedures are illegal and the European Commission regulates these treatments, forbidding the addition of such components [7] due to possible economic fraud and potential health problems associated with consumption of illegally processed tuna [8]. Among the different possible adulterant solutions, the use of nitrite is particularly concerning for food safety. Indeed, nitrite salts are directly related to the so-called \"blue baby syndrome\", an acute syndrome that can occur especially in infants when ingested nitrite reacts with the ferrous group of hemoglobin, which is oxidized to Fe\({}^{3+}\) to form methemoglobin. This compound cannot transport oxygen throughout the body, and this deficiency leads to cyanosis and hypoxia [9]. The possible reaction of ingested nitrite with secondary amines to form \(N\)-nitrosamines is another toxic effect since these compounds, recently reviewed by the European Food Safety Authority, have been classified as pro-carcinogenic by the International Agency for Research on Cancer due to their role in gastrointestinal tumors and stomach cancer development [10; 11; 12]. It is worth noting that in the final remarks of the Scientific Opinion published by EFSA in 2023, entitled \"Risk assessment of N-nitrosamines in food\", the CONTAM Panel concluded that \"the MOE for TCNAs at the P95 exposure is highly likely (98-100% certain) to be less than 10,000 for all age groups, which raises a health concern\". This significant conclusion opens the scenario to new investigation on the presence on \(N\)-nitrosamines in food, focused on establishing specific legal limits in Europe, as have already been adopted in other countries worldwide [13; 14]. Nitrite salts are food additives commonly used with specific legal limits as preservatives in food products such as processed meat. In drinking water, the World Health Organization (WHO) has set a fatal nitrite dose of 3 mg/L (65.2 uM). In the human body, concentrations from 33 to 250 mg of nitrite per kg of body weight are lethal, and those from 0.4 to 200 mg/kg of body weight are enough to cause methemoglobinemia [15; 16]. European Regulation No. 1333/2008 [7] does not permit the addition of nitrite salts in both fresh and processed seafood. Only sodium and potassium nitrate can be used in pickled herring and sprat, with maximum level of 500 mg/kg until 9 October 2025 and 270 mg/kg after this date.