Estimates of the chromium(VI) reducing capacity in human body compartments as a mechanism for attenuating its potential toxicity and carcinogenicity

Abstract

Estimates of the overall reducing capacity of hexavalent chromium(VI) in some human body compartments were made by relating the specific reducing activity of body fluids, cell populations or organs to their average volume, number, or weight. Although these data do not have absolute precision or universal applicability, they provide a rationale for predicting and interpreting the health effects of chromium(VI). The available evidence strongly indicates that chromium(VI) reduction in body fluids and long-lived non-target cells is expected to greatly attenuate its potential toxicity and genotoxicity, to imprint a threshold character to the carcinogenesis process, and to restrict the possible targets of its activity. For example, the chromium(VI) sequestering capacity of whole blood (187-234 mg per individual) and the reducing capacity of red blood cells (at least 93-128 mg) explain why this metal is not a systemic toxicant, except at very high doses, and also explain its lack of carcinogenicity at a distance from the portal of entry into the organism. Reduction by fluids in the digestive tract, e.g. by saliva (0.7-2.1 mg/day) and gastric juice (at least 84-88 mg/day), and sequestration by intestinal bacteria (11-24 mg eliminated daily with feces) account for the poor intestinal absorption of chromium(VI). The chromium(VI) escaping reduction in the digestive tract will be detoxified in the blood of the portal vein system and then in the liver, having an overall reducing capacity of 3300 mg. These processes give reasons for the poor oral toxicity of chromium(VI) and its lack of carcinogenicity when introduced by the oral route or swallowed following reflux from the respiratory tract. In terminal airways chromium(VI) is reduced in the epithelial lining fluid (0.9-1.8 mg) and in pulmonary alveolar macrophages (136 mg). The peripheral lung parenchyma has an overall reducing capacity of 260 mg chromium(VI), with a slightly higher specific activity as compared to the bronchial tree. Therefore, even in the respiratory tract, which is the only consistent target of chromium(VI) carcinogenicity in humans (lung and sinonasal cavities), there are barriers hampering its carcinogenicity. These hurdles could be only overwhelmed under conditions of massive exposure by inhalation, as it occurred in certain work environments prior to the implementation of suitable industrial hygiene measures.

Assessment of occupational exposure to welding fumes by inductively coupled plasma‐mass spectroscopy and by the alkaline Comet assay

“…This lack of correlation might be due to Cr(VI) reduction in body fluids and non target cells, especially in blood. Thus, this reduction could modulate the in vivo genotoxicity of this metal [De Flora et al, 1997].…”

Metals in cigarette smoke

“…Interestingly, there is evidence that the respiratory tract has developed considerable defence mechanisms towards Cr (VI) (23), which is reduced to the non carcinogenic (?) form of Cr (III) (24).…”

What Should We Do With Our Solid Tannery Waste?

“…Rather, its toxicity is some 500-1000 times higher than that of Cr(III) and it is capable of causing mutation, cancer and cell damage (Costa 1997). Its extreme toxicity is attributed to its easy penetrating ability into cells in the form of negative ions (chromate, dichromate) replacing phosphate and sulfate anions (De Flora et al 1997). Once inside the cell, Cr(VI) undergoes step-by-step reduction to Cr(III).…”