Medical Updates: Soil Day Dec 05, 2022
Soil has a considerable effect on human health, whether those effects are positive or negative, direct or indirect. Soil is an important source of nutrients in our food supply and medicines such as antibiotics. However, nutrient imbalances and the presence of human pathogens in the soil biological community can cause negative effects on health. There are also many locations where various elements or chemical compounds are found in soil at toxic levels because of either natural conditions or anthropogenic activities. The soils of urban environments have received increased attention in the last few years, and they too pose a number of human health questions and challenges.
Probably the first recorded depiction of the relation between human health and soil occurs in 1400 bc in the Bible in the book of Numbers where Moses directs the people to ‘see what the land is like . . . .how is the soil …fertile or poor?’ (Numbers 13:18–20). In 400 bce Hippocrates published a list of things that should be considered part of a proper medical evaluation, a list that included. The nature of the ground (Hippocrates, 2010), and in 60 bce Columella wrote about hidden diseases from marshes (Sylvia et al., 1998); in each case advancing the idea that soil is important to human health. However, it was not until the early 1900s that the idea that soil could affect human health started to gain widespread acceptance. McCarrison (1921) concluded that the fertility of a soil determines the nutrient content of food crops, and therefore the health of humans who ate the crops
What Soil do for us? Positive effects
1. Deliberate ingestion of soil (geophagia), particularly clays, is hypothesized to compensate for mineral deficiencies and/or detoxify via absorption of dietary toxins in the gut.
2. Provide substrate/structure on which most humans live
3.Provide a myriad of key ecosystem services
Provisioning services (“products that soil ES make available for human use)
Food and fiber production—soils support the production of a majority of the earth’s supply of food and fiber
Building materials—sand for cement and fill, clay for bricks, wood for building
Biorepository—source of antibiotic-producing organisms
Regulating Services (mediation/moderation of environment in ways that affect health, safety, comfort)
Climate regulation—modulation via cycling of key greenhouse gases including carbon dioxide, methane, and nitrous oxide
Water regulation—storm water mitigation via retention, surface, and ground water purification
Bioremediation—decontamination of toxic waste and/or pathogens via soil microbiota
Cultural Services (“non-material, and normally non-rival and non-consumptive outputs [sic] that affect the physical and mental states of people”)
Aesthetic and recreational—promotes health and well-being through supporting aesthetically pleasing environments and recreational opportunities
What soil do to us? Negative effects
1. Disease/health effects due to soil deficiencies
A. Inherent poor soil fertility—may result in food insecurity with resultant protein-energy malnutrition, growth stunting, immunocompromised ion and death
B. Micronutrient/trace element deficiencies
Iodine—deficiency causes congenital anomalies, mental retardation, hypothyroidism, and goiter. Remerging as a problem in Europe. 740 million people currently affected. 2 billion people at risk
Iron—deficiency results in anemia, fatigue, cognitive impairment, and impaired immunity. 1 to 2 billion people at risk
Selenium—deficiency associated with low glutathione peroxidase levels, impaired antioxidant and redox status, pseudoalbinism, and Keshan disease. 0.5 to 1.0 billion people at risk
Zinc—deficiency impairs wound healing and immunity
1. Disease/health effects due to direct exposure to soils or soil components primarily via:
A. Ingestion
Gastroenteritis—diarrheal disease caused by ingestion of small quantities of soil contaminated with enteric bacterial pathogens (Campylobacter, Escherichia coli, Shigella spp.) or viruses (Norwalk virus) or protozoans (Cryptosporidium parvum)
Helminthiasis—parasitic intestinal infection caused by ingestion of soil containing Ascaris or whipworm eggs
Element toxicity—ingestion of naturally contaminated soils or soils contaminated by anthropogenic activities may cause toxicity most notably due to lead, arsenic, cadmium, and nitrate
Xenobiotic exposure—xenobiotics are synthetic chemicals, typically carbon based, often characterized by long environmental half-lives, and increasing recognized as having endocrine disrupting effects at very low concentrations. Exposure may cause cancer, obesity/metabolic disease, reproductive, developmental, and cognitive anomalies
B. Inhalation
Coccidioidomycosis—pulmonary infection AKA valley fever due to inhalation of dust-borne fungal spores
Mesothelioma—cancer of lining of the lung caused by inhalation of soil dust containing asbestos
Silicosis—pulmonary fibrosis caused by inhalation of silica crystals
Lung cancer—inhalation of radon that naturally occurs in soils and accumulates in basements/underground structures
C. Dermal absorption/penetration
Podoconiosis—chronic debilitating non-filarial elephantiasis of lower extremities due to penetration of skin by fine volcanic soils with resultant chronic inflammation. 1 to 2 million people affected
Tetanus—paralysis caused by wound contamination with soil containing Clostridium tetani spores
Helminthiasis—parasitic intestinal infection caused by penetration of skin by hookworm larvae in soil
