Substance used in the ripening of fruits can cause kidney damage and water and electrolytic disorders

Calcium Carbide (CaC₂) is a chemical substance used in the production of acetylene, steel and in welding¹. Nonetheless, one way of using this substance is as an accelerator for ripening fruits for human consumption, especially with bananas¹. The maturation of bananas and other fruits depends on intrinsic and highly coordinated processes in the fruit, especially if we consider that the maturation stage is the beginning of the senescence process²,³. Ethylene is the phytohormone responsible for initiating the maturation phase of climacteric fruits, such as bananas²,³. Due to demands from the food market, many producers choose to carry out the maturation of fruits artificially, in order to obtain volume and standardization of production³. CaC₂ is a highly alkaline product, and in contact with water it produces calcium hydroxide (Ca(OH)₂) and acetylene gas (C₂H₂). Acetylene gas is a substance analogous to ethylene, which mimics the function of the phytohormone, promoting standardized and rapid fruit maturation¹. However, the use of CaC₂ can produce a fruit with a ripe appearance, but with an immature interior, which leaves the fruit without the expected flavor¹. More importantly, CaC₂ can be a toxic substance, both for consumers and workers involved in fruit production¹–³. CaC₂ irritates the oral and nasal mucosae, in addition to causing gastrointestinal discomfort¹–³. Acetylene gas is soluble in water and can buildup in fruits and affect the neurological system¹. The impurities found in CaC₂, such as traces of arsenic and phosphorus, can lead to acute irritation of the mouth and nose, vomiting, skin ulcers and even kidney damage¹,⁴.

In an article published in the Brazilian Journal of Nephrology⁵, researchers from the University of Benin, Nigeria, reported that female rats fed bananas (Musa paradisíaca) artificially ripened with CaC₂ showed electrolyte and renal alterations. Rats fed naturally ripened bananas showed no such changes. The authors observed a significant increase in plasma concentrations of bicarbonate and a decrease in plasma concentrations of potassium and chlorine in animals fed bananas exposed to CaC₂ when compared to animals fed naturally ripened bananas. In addition, the renal function of these animals seemed to have been affected, with a significant increase in plasma urea and creatinine. These animals also showed alterations in the renal tissue, with glomerular atrophy and tubular necrosis. It is important to note that the serum levels of both chlorine and bicarbonate in the control groups were, interestingly, far below the normal range. Bicarbonate levels around 5 mEq/L and chlorine levels around 45 mEq/L. In any case, the animals fed with fruits ripened with CaC₂ had bicarbonate levels significantly higher than those of the control groups, around 20 mEq/L, and chlorine levels significantly lower than those of the control groups, 30 mEq/L. Therefore, animals fed bananas ripened with CaC₂ showed increased plasma bicarbonate (we cannot say that there was alkalosis, since bicarbonate levels were around 20 mEq/L), hypochloremia and hypokalemia. It is noteworthy that the number of animals per group was three.

As already mentioned at the beginning, CaC₂ is extremely alkalizing in contact with water. Under normal circumstances, the kidneys excrete excess bicarbonate and restore acid-base balance⁶. Normal kidneys have an enormous capacity to excrete large amounts of bicarbonate when ingested chronically⁷. Failure of the kidneys to excrete excess bicarbonate is due to the presence of a mechanism that leads to the maintenance of metabolic alkalosis. The drop in glomerular filtration may explain the decrease in bicarbonate filtration. These animals may be presenting the calcium-alkali syndrome⁸. The calcium-alkali syndrome consists of the triad of hypercalcemia, metabolic alkalosis and acute kidney injury associated with the ingestion of large amounts of absorbable calcium and alkali⁸. The syndrome was originally described in association with the use of milk and sodium bicarbonate for the treatment of peptic ulcers⁸. Unfortunately, serum calcium levels were not measured. Hypochloremia could not be explained by the calcium-alkali syndrome. The presence of hypochloremia in metabolic alkalosis is justified by volume depletion and loss of hydrochloric acid by the stomach. However, there are no reports of vomiting in these animals.

Prohibited in several countries, the use of Calcium Carbide is still allowed in Brazil, although some cities have laws prohibiting its use. It is important to highlight that there are safe ways to manage the maturation of bananas, such as the method used by producers in Borborema, in the state of Paraíba, and described by Brazilian researchers from the State University of Paraíba and the Federal University of Campina Grande³. The researchers reported that the ripening of bananas using leaves of Bowdichia virgilioides Kunth, a plant popularly known as Sucupira-preto, was efficient and safe for consumption³. Thoroughly washing the fruits can help in the partial removal of CaC₂.

References

• ^1.
  Okeke ES, Okagu IU, Okoye CO, Ezeorba TPC. The use of calcium carbide in food and fruit ripening: potential mechanisms of toxicity to humans and future prospects. Toxicology. 2022;468:153112. doi: http://dx.doi.org/10.1016/j.tox.2022.153112. PubMed PMID: 35101591.
  » https://doi.org/10.1016/j.tox.2022.153112
• ^2.
  Maduwanthi SDT, Marapana RAUJ. Induced ripening agents and their effect on fruit quality of banana. Int J Food Sci. 2019;2019:2520179. doi: http://dx.doi.org/10.1155/2019/2520179. PubMed PMID: 31187037.
  » https://doi.org/10.1155/2019/2520179
• ^3.
  Nascimento RC, Freire OO, Ribeiro LS, Araújo MB, Finger FL, Soares MA, et al. Ripening of bananas using Bowdichia virgilioides Kunth leaves. Sci Rep. 2019;9(1):3548. doi: http://dx.doi.org/10.1038/s41598-019-40053-3. PubMed PMID: 30837590.
  » https://doi.org/10.1038/s41598-019-40053-3
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  Pokhrel P. Use of higher ethylene generating fruists for ripening as an alternative to ethynene. J Food Sci Technol Nepal. 2013;8:84–6. doi: http://dx.doi.org/10.3126/jfstn.v8i0.11757.
  » https://doi.org/10.3126/jfstn.v8i0.11757
• ^5.
  Ugbeni OC, Alagbaoso CA. Calcium carbide-ripened plantain induced alterations in plasma electrolytes concentration and kidney function in rats. J Bras Nefrol. 2023. doi: http://dx.doi.org/10.1590/2175-8239-jbn-2022-0101en. PubMed PMID: 36638245.
  » https://doi.org/10.1590/2175-8239-jbn-2022-0101en
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  Zatz R, Rebouças NA, Malnic G. Fundamentos de equilíbrio ácido-base e mecanismos de acidificação urinária. In: Zatz R, Seguro AC, Malnic G, editores. Bases fisiológicas da nefrologia. São Paulo: Atheneu; 2011.
• ^7.
  Emmett M. Metabolic alkalosis: a brief pathophysiologic review. Clin J Am Soc Nephrol. 2020;15(12):1848–56. doi: http://dx.doi.org/10.2215/CJN.16041219. PubMed PMID: 32586924.
  » https://doi.org/10.2215/CJN.16041219
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  Yu ASL, Stubbs JR. The milk-alkali syndrome [Internet]. UpToDate; 2023 [cited 2023 aug 28]. Available from: https://www.uptodate.com/contents/the-milk-alkali-syndrome
  » https://www.uptodate.com/contents/the-milk-alkali-syndrome

Publication Dates

• Publication in this collection
  03 Nov 2023
• Date of issue
  Oct-Dec 2023

History

• Received
  29 Aug 2023
• Accepted
  30 Aug 2023