Occurrence, behaviour, and human exposure pathways and health risks of toxic geogenic contaminants in serpentinitic ultramafic geological environments (SUGEs): A medical geology perspective

Our plain-English summary of Occurrence, behaviour, and human exposure pathways and health risks of toxic geogenic contaminants in serpentinitic ultramafic geological environments (SUGEs): A medical geology perspective, by W. Gwenzi (The Science of the Total Environment, 2020).

The study

• Author: W. Gwenzi
• Journal: The Science of the Total Environment
• Published: 2020;700:134622
• Type of article: Review
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Serpentinitic ultramafic geological environments (SUGEs) contain toxic geogenic contaminants (TGCs). Yet comprehensive reviews on the medical geology of SUGEs are still lacking. The current paper posits that TGCs occur widely in SUGEs, and pose human health risks. The objectives of the review are to: (1) highlight the nature, occurrence and behaviour of TGCs associated with SUGEs; (2) discuss the human intake pathways and health risks of TGCs; (4) identify the key risk factors predisposing human health to TGCs particularly in Africa; and (5) highlight key knowledge gaps and future research directions. TGCs of human health concern in SUGEs include chrysotile asbestos, toxic metals (Fe, Cr, Ni, Mn, Zn, Co), and rare earth elements. Human intake of TGCs occur via inhalation, and ingestion of contaminated drinking water, wild foods, medicinal plants, animal foods, and geophagic earths. Occupational exposure may occur in the mining, milling, sculpturing, engraving, and carving industries. African populations are particularly at high risk due to: (1) widespread consumption of wild foods, medicinal plants, untreated drinking water, and geophagic earths; (2) weak and poorly enforced environmental, occupational, and public health regulations; and (3) lack of human health surveillance systems. Human health risks of chrysotile include asbestosis, cancers, and mesothelioma. Toxic metals are redox active, thus generate reactive oxygen species causing oxidative stress. Dietary intake of iron and geophagy may increase the iron overload among native Africans who are genetically predisposed to such health risks. Synergistic interactions among TGCs particularly chrysotile and toxic metals may have adverse human health effects. The occurrence of SUGEs, coupled with the several risk factors in Africa, provides a unique and ideal setting for investigating the relationships between TGCs and human health risks. A conceptual framework for human health risk assessment and mitigation, and future research direction are highlighted.

Copyright © 2019 Elsevier B.V. All rights reserved.

In plain English

This article was a narrative review by a single author from the University of Zimbabwe. It was based on a qualitative analysis of literature found by searching Scopus, Web of Science, ScienceDirect and Google Scholar. It examined toxic substances in serpentine-rich rocks and soils: chrysotile asbestos; metals including iron, chromium, nickel, manganese, zinc and cobalt; and rare earth elements. The review described how these substances can reach people. At work, the route is breathing dust in mining, milling, sculpting, carving and engraving. Away from work, the routes are dust, drinking water, wild foods, medicinal plants, animal foods and deliberately eaten earth. It cited the position of the World Health Organization and the International Agency for Research on Cancer that chrysotile is carcinogenic. It also described 1991 studies of asbestos miners and millers in Zimbabwe. The author noted that evidence directly linking toxic metals in these settings to human illness remained weak, and that data on combined effects were limited. The author concluded that health risks could be significantly higher in developing countries, especially in rural Africa, and proposed a six-step risk assessment framework.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Narrative literature review, based on a Boolean search of scholarly databases and qualitative analysis of the literature
• Who was studied: No study population. The review covered published literature on serpentinitic ultramafic geological environments worldwide, with particular attention to Africa and Zimbabwe (for example, the Great Dyke and the former Shabani-Mashava chrysotile mine).
• Exposure: Chrysotile asbestos, toxic metals (Fe, Cr, Ni, Mn, Zn, Co) and rare earth elements from serpentine-rich rocks and soils. The routes covered were inhalation of dust at work (mining, milling, sculpturing, engraving, carving) and, outside work, dust, drinking water, wild foods, medicinal plants, animal foods and geophagic earths.
• Main results:
  • The review stated that workers are exposed during mining and industrial processing mainly by breathing contaminated dust.
  • The review cited the IARC and WHO position that asbestos, including chrysotile, is carcinogenic.
  • The review described an earlier Zimbabwean study (Cullen and Baloyi, 1991) that analysed 51 individuals with asbestos exposure who had been compensated for asbestos-related disease. It reported that the authors of that work concluded that morbid asbestosis, non-malignant pleural disease, malignant mesothelioma and lung cancer were also common among workers in the asbestos mines and mills.
  • The review described cited studies reporting that the toxicity of asbestos, in terms of oxidative stress and DNA strand breakage, is enhanced in the presence of iron.
  • The author stated that evidence directly linking toxic metals in these environments to adverse human health effects remains weak.
• The authors' conclusion: The author concluded that the health risks of these contaminants could be significantly higher in developing countries than in developed ones. The author argued that conditions in Africa offer a setting for research to establish any direct link between these contaminants and human health risks, and proposed a six-step framework for risk assessment and mitigation.
• Limitations the authors state:
  • The author noted that epidemiological data on synergistic interactions among these contaminants and other stressors remain limited.
  • The author noted that limited data exist on asbestos and other contaminants in airborne particulates in Africa and other developing countries.
  • The author noted that most cited studies reported only total metal concentrations, without information on bioavailability, and cautioned against inferring health risks from total concentrations.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Occupational Exposure, Mesothelioma, Reactive Oxygen Species (ROS), Oxidative Stress.

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