Portals of Vanadium Entry
Through Digestive Tract
In vertebrates, vanadium enters the organism principally via the digestive and respiratory tracts through food ingestion and air inhalation (Rehder 2008, 2015). The estimated daily dietary intake in the United States is 10-60 pg/day, and it is a little higher for processed foods. A little amount of vanadium also gets inside our body through drinking water (Health, Substances, and Registry 2012). Studies in animals have shown that less than 5% of the ingested vanadiumis absorbed while the rest is excreted via the feces. On the contrary, very little vanadium (0.2-1%) is absorbed in the human gut. Dietary composition, fasting, and speciation are the various factors on which extent of vanadium vary from individual to individual (Wilk et al. 2017, Ma et al. 2018, Greim 2009). Gastrointestinal problems such as abdominal pain, cramping, discomfort, irregular bowel discharge, nausea, and vomiting start showing only at dosage above 15 mg vanadium/day after atleast a period of 2weeks (Goldfine et al. 2000, Afkhami-Arekani et al. 2008). Most of the dietary vanadium is usually excreted in the feces, meaning that the vanadium accumulation in the body does not pose any significant threat (Korbecki et al. 2012, Costa Pessoa and Tomaz 2010).
Through Respiratory Tract
Inhalation of vanadium constitutes the chief portal of entry of the metal inside the human body. This has been established unequivocally through data from industry workers as well as studies in human and laboratory animals. The size and nature (organic/inorganic) of vanadium-containing particles and the solubility of vanadium compounds are the governing factors behind absorption rate of the metal in the respiratory tract. For example, insoluble vanadium pentoxide is relatively rapidly expelled by lungs in animals after sudden acute exposure, but the process occurs at a significantly slower rate when exposure to vanadium takes place on a regular basis. This occurs because over time the metal is slowly deposited in the lungs and tends to remain there. Soluble vanadium compounds are partially absorbed, but the extent of absorption is yet to be determined accurately. Adverse toxicity effects of vanadium inhalation have been reported in humans and animals at concentrations substantially higher than those found in environments. Workers regularly inhaling vanadium pentoxide dust have been shown to be affected from diverse respiratory obstructions and airway irritation (e.g., coughing, wheezing, and sore throat). Although the effects persist for days or weeks after the end of initial exposure, they do not generally affect lung function (Rehder 2013, Fallahi et al. 2018, Zhu et al. 2016, Yu et al. 2011, Wei et al. 2015). However, the effects are more pronounced in animal models with concomitant development of many lung lesions including alveo- lar/bronchiolar hyperplasia, inflammation, and fibrosis.