So far, I have covered sources of soil pollution from agricultural, industrial, urban activities as well as war, and the various effects they have on soil ecosystem, human health and biodiversity. The sources of soil pollution are varied, from the primary sector to the final stages of producing everyday products.
The health impacts of soil pollution have been recognized by the UN Sustainable Development Goal 3 regarding health and wellbeing, specifically under the target 3.9:
“By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination”
Exposure pathways
Humans are exposed to soil pollutants through a few main pathways:
Accidental or intentional ingestion of contaminated soil particles, food, and dust
Dermal contact
Inhalation of soil particles, contaminated dust, and vapors (indoors and outdoors)
Soil pollution exposure most commonly occurs through the food chain. 95% of the world's food (both plant and animal products) are produced directly or indirectly from the soil, depending on the soil for nutrients. Health effects of exposure to soil contaminants depend on several factors, including the concentration of the contaminant, exposure route, amount and duration of exposure, and personal susceptibility.
In Singapore, although agricultural activity is limited, soils can be polluted through local urban and industrial activities such as construction works. As more than 90% of the food is imported in Singapore, imported products could have been grown in contaminated soils. WHO has identified ten top contaminants of human health concern, nine of which are soil contaminants. These organic and inorganic contaminants exhibit toxicity mechanisms including endocrine disruptors, neurotoxins, carcinogens, or teratogens.
For example, mercury, a chemical on the WHO list, can transfer into soils and plants, and enter livestock. Methylmercury can accumulate in the kidneys and liver of cows and sheep. The resulting animal products that are consumed by humans can affect health. As I mentioned in my post about gold mining, another exposure route could be through occupational hazards, as small-scale artisanal gold miners are exposed to methylmercury. Some of the main symptoms of mercury/methylmercury exposure include intellectual disability, loss of neural cells, cerebral palsy, deafness, and blindness.
How many people die due to soil pollution?
As contaminants often move relatively freely between soil, plants, animals, the atmosphere, and water bodies, it is often difficult to discern the exact source of the pollution. This is one of the reasons why there is no accurate national or global estimate of the disease burden attributed solely to soil pollution or soil-borne disease. Even in developed countries, measures to examine and control polluted soils are not precautionary and are often implemented after health impacts are observed. It is also difficult to establish strong cause and effect relationships between soil pollution and disease burden or deaths associated with exposure. Many diseases might occur decades after exposure like cancer. Establishing a global monitoring system, as well as harmonized and reliable soil pollution indicators are needed in order to monitor progress towards achieving the SDG target.
Emerging threat: soil pollution and antibiotic resistance
Soils are the dumping ground for a variety of medical wastes, including pharmaceuticals and veterinary medicines through improper disposal, livestock production (e.g. manure runoff/application into the soil). When these medicines and wastes enter the soil, they can generate resistance in soil microorganisms. A study identified that soils polluted with heavy metals had a higher level of bacteria with antibiotic resistance genes. Bacteria is a natural component of soils, with up to a billion bacteria in a teaspoon of soil. However, recent research has shown that when the bacteria are exposed to heavy metals or radionuclides, they can develop resistance towards pollutants as well as antibiotics (Thomas et al. 2020). Antibiotic resistance is a global health threat, leading to increased mortality, prolonged hospital stays, higher medical costs and decreases potential to produce new medicines.
Who is most affected by soil pollution?
The rise in soil pollution globally and its associated health impacts disproportionately burdens the most vulnerable, as I've unpacked on this blog, along the lines of socioeconomic class, ethnicity, religion, gender, disability and age.
Furthermore, soil pollution incurs economic costs, including the loss of crop yields, decreased soil productivity, the spread of disease, polluted water and unsafe food. The increased use of agrochemicals to compensate for the reduction in soil productivity and need for soil remediation also leads to expenditure. In China, around 12 million tonnes of grain are contaminated by heavy metals every year, which costs US 2 billion annually (Qi, 2007).
How can these socioeconomic and health costs be addressed in the effort to save our soils? It is imperative to translate the science we have on the drivers and effects of soil pollution to policy, action, and legislation on both national and international levels - stay tuned for the next few posts on this!
References
FAO and UNEP (2021). Global assessment of soil pollution: Report.
Thomas, J. C., Oladeinde, A., Kieran, T. J., Finger, J. W., Bayona‐Vásquez, N. J., Cartee, J. C., Beasley, J. C., Seaman, J. C., McArthur, J. V., Rhodes, O. E., & Glenn, T. C. (2020). Co‐occurrence of antibiotic, biocide, and heavy metal resistance genes in bacteria from metal and radionuclide contaminated soils at the Savannah River Site. Microbial Biotechnology, 13(4), 1179–1200. https://doi.org/10.1111/1751-7915.13578
Qi, X. (2020, May 14). Facing up to “invisible pollution.” China Dialogue. https://chinadialogue.net/en/pollution/724-facing-up-to-invisible-pollution/