Biological Effects of Human Exposure to Environmental Cadmium

Abstract

Cadmium (Cd) is a toxic metal for the human organism and for all ecosystems. Cd is naturally found at low levels; however, higher amounts of Cd in the environment result from human activities as it spreads into the air and water in the form of micropollutants as a consequence of industrial processes, pollution, waste incineration, and electronic waste recycling. The human body has a limited ability to respond to Cd exposure since the metal does not undergo metabolic degradation into less toxic species and is only poorly excreted. The extremely long biological half-life of Cd essentially makes it a cumulative toxin; chronic exposure causes harmful effects from the metal stored in the organs. The present paper considers exposure and potential health concerns due to environmental cadmium. Exposure to Cd compounds is primarily associated with an elevated risk of lung, kidney, prostate, and pancreatic cancer. Cd has also been linked to cancers of the breast, urinary system, and bladder. The multiple mechanisms of Cd-induced carcinogenesis include oxidative stress with the inhibition of antioxidant enzymes, the promotion of lipid peroxidation, and interference with DNA repair systems. Cd²⁺ can also replace essential metal ions, including redox-active ones. A total of 12 cancer types associated with specific genes coding for the Cd-metalloproteome were identified in this work. In addition, we summarize the proper treatments of Cd poisoning, based on the use of selected Cd detoxifying agents and chelators, and the potential for preventive approaches to counteract its chronic exposure.

Keywords: cadmium; cadmium exposure; cadmium toxicity; chronic exposure; protein targets.

Figure 1

Examples of Cd²⁺ coordination environment in biological systems: (a) regular tetrahedral Cd²⁺ complexed with Hah1 metallochaperone protein (Protein Data Bank PDB 1FE0, [21]); (b) regular octahedral Cd²⁺ complexed with cytochrome c oxidase (PDB 2EIK, [22]); (c) a cluster of Cd²⁺ complexed with metallothionein-1 (PDB 1DFT, [23]).

Figure 2

Percentage distribution of geometries for mononuclear Cd²⁺ complexes in proteins, according to the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB PDB).

Figure 3

Percentage distribution of metal ions substituted by Cd²⁺, according to the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB PDB).

Figure 4

Outcomes of cadmium exposure.

Figure 5

The 12 cancer types associated with specific gene-encoding Cd-metalloproteomes.