Heavy metals in vegetables sold in some cities in the Visayas, Philippines

Every time we buy vegetables in the market, we do not doubt the quality of these farm products. We think they are clean, safe, nutritious and good for our health.

But the worsening environmental pollution due to the overuse and misuse of agricultural chemicals such as pesticides, the improper waste disposal, the manufacturing industry, and the transportation system may be affecting the quality of the food crops we eat everyday. Specifically, heavy metals most of which are toxic to humans at elevated concentrations, are starting to contaminate the vegetables we love to eat.

The scientific principle is simple: a contaminated soil will generally produce contaminated crops.

An interesting and very relevant student research conducted a few years ago revealed such alarming reality. Conducted to determine and compare the Pb, Cu and Zn contents of Alugbati (Basella rubra), Ampalaya (Momordica charantia), Kalabasa (Cucurbita maxima), Kangkong (Ipomoea aquatica), Pechay (Brassica rapa), and Talong (Solanum melongena) sold in markets in the cities of Baybay, Ormoc, and Tacloban (Leyte, Philippines), the study revealed that Ampalaya from Tacloban and Baybay contained excessive levels of Cu and may pose health problems to consumers. 

Likewise, Pechay from Baybay, Ormoc and Tacloban exceeded the safe level for Zn. All vegetable samples collected from the three cities were not contaminated with Pb. Cu and Zn levels varied with crop (vegetable) species and origin (production area). 

The results are very relevant in that they support and confirm the fear among consumers that some food crops sold in the local markets are not safe and may be one of the reasons for the various health problems experienced by many people.

The study was conducted in 2012 by Anna Luisa Ventulan, Christine Gay Cala, and Johannes Reiner Asio, all senior students at VSU Laboratory High School. The research adviser was Luz Geneston Asio of the Central Analytical Services Laboratory, Visayas State University, Baybay City, Leyte.

Some notes on the soils and use of fertilizers and pesticides by vegetable farmers in Claveria, Misamis Oriental, Philippines

The gently rolling topography which typifies a large portion of the volcanic landscape in Claveria makes it ideal for intensive large-scale vegetable production. The widely grown vegetables include cabbage, beans, tomato, sweet pepper and eggplant.

The breathtaking volcanic landscape of Claveria, Misamis Oriental

But the strongly weathered soils which range from Oxisols in the lower slopes (about 400 to 600 m above sea level or asl) to Ultisols in the upper slopes (about 600 to 900m asl) are a major constraint to vegetable production in the area. Oxisols (also called Ferralsols) and Ultisols (also called Alisols and Acrisols) are clayey, reddish, acidic and nutrient-poor soils although they generally have good physical properties like good structure and moderate to high porosity. As in other volcanic landscapes, the oldest and most infertile soils (Oxisols) are formed on the older and stable lower slopes.

Dr. Apol & Nelds Gonzaga, Ruby Gabaca, Dr. Steve Harper & myself in front of an Ultisol soil at 920m asl. 

Farmers are apparently aware of the chemical and nutrient limitations inherent in these soils. That is why they apply lime and a variety of chemical and organic fertilizers. Rates of application are, however, not based on soil/plant tissue analysis but on what the farmers perceive as necessary. Thus, the rates appear to be insufficient in the case of lime, but excessive for the chemical fertilizers. This undoubtedly increases the production cost and can lead to more soil and environmental problems like acidification and groundwater pollution, respectively.

Heavy fertilizer application is done starting at planting of vegetables

Pest and diseases are also greatly affecting vegetable production in the Claveria landscape. As a result, farmers practice excessive application of pesticides which poses a serious threat to the health of the farming families, the consumers in urban centers, and the environment in general. The lack of awareness among farmers about the proper application of pesticides can be seen from their improper handling of these hazardous chemicals and from the fact that they just leave the pesticide containers at the farm borders.

It is common for farmers to mix two pesticides with water and spray the cocktail to the vegetables twice a week

The above observations strongly justify the urgent need for research on soil and nutrient management as well as integrated pest management in Claveria.

Environmental pollution: the case of Xenobiotics

Xenobiotics are chemical substances that are foreign to the biological system. They include naturally occurring compounds, drugs, and environmental agents (Mondofacto online medical dictionary at www.mondofacto.com). The classes of xenobiotics include pesticides, polyaromatic hydrocarbons (PAHs), polychlorinated aromatics, solvents, hydrocarbons, and others (surfactants, silicones, and plastics).

Xenobiotics levels in soils are generally low (less than 100 ppm) unless they are concentrated by application as in the case of pesticides, by spills or by waste disposal. They can occur in soils in solid, dissolved, and gaseous phases and all undergo microbial and abiotic (chemical) transformations (Logan, 2000).

Photo source: www.cleanwaterfund.com

Pesticides are the most important xenobiotic pollutants because of their widespread use in agriculture. In many developing countries, the unregulated use of pesticides by poor farmers contributes not only to environmental pollution but to health problems as well.

In the soil, pesticides can be temporarily fixed through adsorption by soil particles. The persistence or decomposition of pesticides in the soil is influenced by soil moisture, organic matter content, redox potential, soil acidity, soil temperature, texture, adsorption potential, and clay minerals (Schactschabel et al., 1998; Sonon and Schwab, 2004).

References

Logan, T.J. 2000. Soils and environmental quality. In: Handbook of Soil Science (M.E. Sumner, ed.). CRC Press, Boca Raton, pp: G155-G169.

Schactschabel P., H.P. Blume, G. Brümmer, K.H. Hartge and U. Schwertmann. 1998. Lehrbuch der Bodenkunde (14th ed.). Ferdinand Enke Verlag, Stuttgart.

Sonon, L.S. and P.A. Scwab. 2004. Transport and persistence of nitrate, atrazine, and alachlor in large intact soil columns under two levels of moisture contents. Soil Science 169: 541-553.

The role of mycorrhiza in the mineral nutrition of plants

Mycorrhiza is the association between fungi and the roots of higher plants. The term was introduced by the German scientist A.B. Frank in 1885 (Mengel and Kirkby, 2001). Mycorrhiza is considered as the most widespread association between microorganisms and higher plants. On a global scale, between 86% and 94% of plants are mycorrhizal (Brundrett 2009). All Gymnosperms as well as 83% and 79% of dicotyledonous and monocotyledonous plants, respectively, are mychorrhizal (Marschner 1995). Nonmycorrhizal plants can be found in stressed soil environments (very dry or saline, waterlogged, severely disturbed as in mining areas, infertile) or even in very fertile soils. Mycorrhizas (or mycorrhizae) are absent under all environmental conditions in the Cruciferae and Chenopodiaceae (Marschner, 1995). Generally, in root-fungus association the fungus is strongly or wholly dependent on the higher plant, whereas the plant may or may not benefit from the association. It is not also essential for plant survival except in some plants like orchids. Mycorrhizal associations are therefore either mutualistic, neutral, or parasitic depending on the circumstances although mutualism is the dominant type.

Groups of mycorrhizas

Two mycorrhizal groups according to how the fungal mycelium relates to the root structure:
a) Endomycorrhizas. The fungi live inside the cortical cells of the roots and also grow intercellularly. The best known type is the vesicular-arbuscular mycorrhiza (VAM). This is widespread in cultivated soils.
b) Ectomycorrhizas. This group of mycorrhiza occurs mainly on roots of woody plants and only occasionally on herbaceous and graminaceous perennial plants. Some temperate tree species like beech, oak, spruce and pine cannot survive without ectomycorrhiza (Schachtschabel et al., 1998). They form a sheath or mantle of fungal mycelium over the surface of fine roots. The hyphae penetrate into the intercellular spaces of the root cortex and it extends outward into the soil.

Role of mycorrhizas in the mineral nutrition of host plants

Mycorrhizas are very important in the uptake of nutrients such as P, N, K, Cu, Zn and Ca by plants especially in soils low in these nutrients. Since P is the most limiting nutrient in tropical soils, mycorrhizas are vital for improving P nutrition particularly for cultivated plants. External hyphae can absorb and translocate P to the host from soil outside the root depletion zone. The thin mycorrhizal hyphae (2-4 μm in diameter) are able to penetrate soil pores not accessible to the root hairs which are about five times larger than the hyphae (Kirkby and Mengel, 2001). For example, studies have shown that the heavily mycorrhizal root of cassava enables it to grow well in phosphate-deficient soils where other crops fail (Wild, 1993). Also, a long-term study at the National Abaca Research Center at VSU (Armecin and Geneston-Asio, 2004) has provided the first clear evidence that abaca plant (Musa textilis) is mycorrhizal although colonization was relatively low (18-22%). In alkaline soils, mycorrhiza can prevent iron and manganese deficiencies. Mycorrhizas are also known to protect the plant from soil borne pathogens.

Recently, Lambers et al. (2010) reported that terrestrial plants (except epiphytes, parasites and carnivorous species) acquire most mineral nutrients from the soil primarily via two pathways: 1) direct absorption through the roots, and 2) indirect absorption through symbiotic mycorrhizal fungi. The majority of plants can take up phosphorus via both pathways but depend primarily on mycorrhizal fungi to acquire phosphorus.

References

Armecin RB and LG Asio. 2004. Effects of vesicular-arbuscular mycorrhizal fungi inoculation on Abaca (Musa textilis). Unpublished research report. NARC, VSU, Baybay, Leyte.
Brundrett, M. 2009. Plant and Soil 320: 37-77.
Lambers H, MC Brundrett MC, JA Raven and SD Hopper. 2010. Plant and Soil 334:11-31.
Marschner, H. 1995. Mineral Nutrition of Higher Plants. 2nd ed., Academic Press, London.
Mengel, K. and E.A. Kirkby. 2001. Principles of Plant Nutrition (5thed.). Kluwer Academic Publishers, Dordrecht, 849pp.
Schactschabel P., H.P. Blume, G. Brümmer, K.H. Hartge and U. Schwertmann. 1998. Lehrbuch der Bodenkunde (14th ed.). Ferdinand Enke Verlag, Stuttgart, 494pp.
Wild, A 1993. Soils and the Environment. Cambridge University Press, Cambridge, 287pp.

Photo Sources:
1. G. Quinn at http://www.finegardening.com/
2. Nathan Brandt, Iowa State University Extension News at http://www.extension.iostate.edu/

Lead pollution due to vehicular emissions in urban areas in the Philippines

Lead (Pb) has been known to be toxic since ancient times. It is a widespread contaminant in soils and Pb poisoning is one of the most prevalent public health problems in many parts of the world. It was the first metal to be linked with failures in reproduction. It can cross the placenta easily. It also affects the brain, causing hyperactivity and deficiency in the fine motor functions, thus, it results in damage to the brain. The nervous systems of children are especially sensitive to Pb leading to retardation. Pb is cardiotoxic and contributes to cardiomyopathy (disease of the heart muscle leading to the enlargement of the heart).

Pb is released into the environment from the weathering of Pb-containing rocks, the industry, and the combustion of fossil fuels. Emissions from vehicles are thus a major source of environmental contamination by Pb especially in cities. Ona et al. (2006) conducted a study that looked into Pb pollution in selected urban areas in the Philippines with the following objectives: (1) to determine the levels of Pb in soil from selected urbanized cities in central region of the Philippines; (2) to identify areas with soil Pb concentration values that exceed estimated natural concentrations and allow- able limits; and (3) to determine the possible sources that contribute to elevated soil Pb concentration (if any) in the study area.

The study focused on the determination of Pb levels in soils of selected cities in Luzon, Philippines. The sites included: Site 1 – Tarlac City in Tarlac; Site 2 – Cabanatuan City in Nueva Ecija; Site 3 – Malolos City in Bulacan; Site 4 – San Fernando City in Pampanga; Site 5 – Balanga City in Bataan; and Site 6 – Olongapo City in Zambales. Soil samples were collected from areas along major thoroughfares regularly tra- versed by tricycles, passenger jeepneys, cars, vans, trucks, buses, and other motor vehicles. Soil samples were collected from five sampling sites in each of the study areas. Samples from the selected sampling sites were obtained approximately 2 to 3 meters from the road. Analysis of the soil samples for Pb content was conducted using an atomic absorption spectrophotometer.

Findings revealed Pb levels ranging from 1.5 to 251 mg kg–1 in all the soil samples collected from the 30 sampling sites in the six cities. Elevated soil Pb levels i.e.greater than 25 mg kg–1 Pb) were observed in five out of the six cities sampled. Site 4 showed the highest Pb concentration (73.9 ± 94.4 mg kg–1), followed by Site 6 (56.3 ± 17.1 mg kg–1), Site 3 (52.0 ± 33.1 mg kg–1), Site 5 (39.3 ± 19.0 mg kg–1), and Site 2 (38.4 ± 33.2 mg kg–1). Soil Pb level in Site 1 (16.8 ± 12.2 mg kg–1) was within the estimated natural Pb concentration range of 5 to 25 mg kg–1. The study found that the average soil Pb concentration from the six cities studied were below the maximum tolerable limit according to World Health Organization (WHO) standards. The high Pb concentration in Site 4 was attributed by the authors mainly to vehicular emission.

The researchers concluded that "only one (San Juan in Site 4) of the thirty sampling sites showed a Pb concentration above the WHO permissible limit of 100 mg kg–1. San Juan in Site 4 had a Pb concentration of >250 mg kg–1. On the average, elevated Pb concentration was evident in the soil samples from San Fernando, Olongapo, Malolos, Balanga, and Cabanatuan. The average soil Pb concentrations in these cities exceeded the maximum estimated natural soil Pb concentration of 25 mg kg–1. Average soil Pb concentration in Site 1 (16.8 mg kg–1) was well within the estimated natural concentration range of 5 to 25 mg kg–1. Data gathered from the study areas showed that elevated levels of Pb in soil were due primarily to vehicular emissions and partly to igneous activity."

Reference
Ona LF, Alberto AMP, Prudente JA and Sigua GC. 2006. Levels of lead in urban soils from selected cities in a Central Region of the Philippines. Environ Sci & Pollut Res 13 (3) 177 – 183

The problem of high levels of nickel in soils and plants in the ultramafic area in Samar, Philippines

Contributed by Janice P. Susaya, Sejong University, Seoul, Korea


One of the heavy metals that commonly occur in elevated amounts in natural ecosystems is nickel (Ni). Ni is considered an essential micronutrient for plants, humans, and animals. It can exist in trace amounts in air, food, drinking water, and soils. Although Ni plays an important role in the metabolism of humans and animals, its intake in excesssive amounts or over a prolonged period could pose health ricsks. Studies have shown that children living in polluted areas have hypertrophy of tonsils, enlarged lymphatic nodes, and enlarged livers. There is also evidence that soluble Ni particulate is linked to acute lung injury.

High Ni levels in natural ecosystems commonly come from ultramafic rocks (also called ultrabasic rocks). These are intrusive igneous rocks containing less than 45% silica (SiO2) with high concentrations of Ni, Mg, Fe, Cr, and Co. They are found in many places around the world and are common in many places in the Philippine like in Salcedo in the island of Samar.The watershed has a highly weathered soil (Oxisol) derived from the weathering of ultramafic rock. Previous studies conducted in the watershed revealed excessive levels of Ni, Cu, and Cr in the soil. Many farmers also complain of unexplained health problems which may be related to heavy metal toxicity.

In a study conducted in the Salcedo watershed and recently published in the international scientific journal Environmental Monitoring and Assessment, Susaya and co-workers (Susaya et al., 2009) evaluated the degree of Ni contamination in soils and plants in the watershed. The plants sampled included native species (non-food) such as Phyllanthus amarus, Melastoma affine, and Stachytarpeta jamaicensis as well as cultivated food crops like Calocasia esculenta, Citrullus vulgaris, Artocarpus heterophylla, Moringa oleifera, Psidium guajava, Lycopersicon esculentum, and Solanum melongena.

Results of the study showed that the quantity of total Ni in the soil was significantly high with a mean of 1,409 mg kg-1 while the available Ni was low with a mean of 8.66 mg kg-1. As the levels of total Ni greatly exceeded the maximum allowable concentration for agricultural soils, the site is not suitable for agricultural purposes. Available Ni levels were low due to the tight binding between Ni and the soil components. This explains why all plants investigated did not met the criterion for a Ni hyperaccumulator plant. Comparison of Ni levels between the food plants sampled and its recommended daily intake (RDI) suggests that consumption of a particular food plant grown in the study area is unlikely to pose health problems. However, prolonged consumption of a given food plant with high Ni level or combined consumption of different food plants with high Ni levels can induce accumulation of Ni above the RDI and thus could cause health problems.

Reference

Susaya JP, KH Kim, VB Asio, ZS Chen, and IA Navarrete. 2009. Quantifying nickel in soils and plants in the ultramafic area in Philippines. Environmental Monitoring and Assessment (now available online at http://www.springer.com/environment/environmental+toxicology/journal/10661)

Heavy metals in the environment and their health effects

Heavy metals have a density of 6.0 g/cm3 or more (much higher than the average particle density of soils which is 2.65 g/cm3) and occur naturally in rocks but concentrations are frequently elevated as a result of contamination. The most important heavy metals with regard to potential hazards and occurrence in contaminated soils are arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb) and zinc (Zn).

The sources of heavy metal pollutants are metal mining, metal smelting, metallurgical industries, and other metal-using industries, waste disposal, corrosions of metals in use, agriculture and forestry, forestry, fossil fuel combustion, and sports and leisure activities. Heavy metal contamination affects large areas worldwide. Hot spots of heavy metal pollution are located close to industrial sites, around large cities, and in the vicinity of mining and smelting plants. Agriculture in these areas faces major problems due to heavy metal transfer into crops and subsequently into the food chain.

Health effects of selected heavy metals

Arsenic (As). Arsenic is well-known as a poison and a carcinogen. It has an average concentration in the soil of 5 to 6 mg/kg. Its amount in the soil is related to rock type and industrial activity.

Cadmium (Cd). Its toxicity is linked with the reproduction problem because it affects sperm and reduces birth weight. It is a potential carcinogen and seems to be a causal factor in cardiovascular diseases and hypertension. Large concentrations of Cd in the soil are associated with parent material (black slates) and most are manmade (burning of fossil fuels, application of fertilizers, sewage sludge, plastic waste).

Chromium (Cr). It is required for carbohydrate and lipid metabolism and the utilization of amino acids. Its biological function is also closely associated with that of insulin and most Cr-stimulated reactions depend on insulin. However, excessive amounts can cause toxicity. Toxic levels are common in soils applied with sewage sludge.

Lead (Pb). This has been known to be toxic since the 2nd century BC in Greece. It is a widespread contaminant in soils. Lead poisoning is one of the most prevalent public health problems in many parts of the world. It was the first metal to be linked with failures in reproduction. It can cross the placenta easily. It also affects the brain, causing hyperactivity and deficiency in the fine motor functions, thus, it results in damage to the brain. The nervous systems of children are especially sensitive to Pb leading to retardation. It is also cardiotoxic and contributes to cardiomyopathy (disease of the heart muscle leading to the enlargement of the heart).

Mercury (Hg). This heavy metal is toxic even at low concentrations to a wide range of organisms including humans. The organic form of mercury can be particularly toxic, and the methyl-and ethyl-forms have been the cause of several major epidemics of poisoning in humans resulting from the ingestion of contaminated food, e.g. fish. Two major epidemics in Japan were caused by the release of methyl and other mercury compounds from an industrial site followed by the accumulation of the chemicals in edible fish. The poisoning became well-known as Minamata disease.

Nickel (Ni). Nickel occurs in the environment only at very low levels. Humans use nickel for many applications like the use of nickel as an ingredient of steel and other metal products. Foodstuffs have a low natural content of nickel but high amounts can occur in food crops grown in polluted soils. Humans may also be exposed to nickel by inhalation, drinking water, smoking, and eating contaminated food. Uptake of high quantities of nickel can cause cancer, respiratory failure, birth defects, allergies, and heart failure (www. Lenntech.com/periodic-chart-elements/Ni-en.htm)

References

Oliver, M.A. 1997. Soil and human health: a review. European Journal of Soil Science 48: 573-592.
Puschenreiter M., O Horak, W. Friesel, and W. Hartl. 2005. Low-cost agricultural measures to reduce heavy metal transfer into the food chain- a review. Plant Soil Environ 51: 1-11.
Susaya JP. 2007. MSc thesis. Institute of Tropical Ecology, Visayas State University, Baybay, Leyte, Philippines.

Environmental pollution and the safety of herbal and alternative medicinal products

There is scientific evidence that many over-the-counter health foods, neutraceuticals, and alternative medicinal products may not be safe. This was revealed in a paper written by Dr. K. Chan of Hongkong Baptist University and published in the international scientific journal Chemosphere.

The paper concluded that “the increase in popularity of such products has brought concerns and fears over the professionalism of practitioners and the quality, efficacy, and safety of their treatment methods and products from herbal and natural sources. These products maybe contaminated with excessive or banned pesticides, microbial contaminants, heavy metals, chemical toxins or adulterated with orthodox drugs."

"The excessive pesticides, microbial contaminants and heavy metals maybe related to the source of these herbal materials if they are grown under contaminated environment or during the collection of these plant materials. Chemical toxins may come from unfavorable or wrong storage conditions or chemical treatment due to storage. The presence of orthodox drugs maybe related to unprofessional practice of manufacturers."

Just a little explanation for the above. Plants growing in polluted soils may absorb the pollutants like heavy metals, pesticides and other harmful substances and store them in their tissues. Studies have shown (e.g. Susaya, 2007) that succulent plant species generally absorb high amounts of heavy metals from the soil. The pesticides may also come from excessive pesticide application to control pests during the production of the herbal plants.

The article is just a reminder to all of us. It may not be true to the products that you are now using. But it may turn out that the fresh herbal plants that we can get from our own backyard maybe safer than the beautifully packed but expensive ones produced somewhere else.

(Photo shows part of the medicinal plant garden of a 12th century castle along Rhein River in Germany.)

Reference

Chan K. 2003. Some aspects of toxic contaminants in herbal medicines. Chemosphere 52: 1361-1371

Clay minerals in soil have antibacterial properties

Clay minerals are a major component of soils. They are an important source of negative charge which enable the soil to hold nutrients and pollutants. In recent years, the medicinal effect of clay minerals has gained increased interest among medical researchers.

In a recent paper in the Journal of Antimicrobial Chemotherapy, Haydel et al. (2008) reported:
"The capacity to properly address the worldwide incidence of infectious diseases lies in the ability to detect, prevent, and effectively treat these infections. Therefore, identifying and analyzing inhibitory agents are worthwhile endeavors in an era when few new classes of effective antimicrobials have been developed. The use of geological nanomaterials to heal skin infections has been evident since earliest recorded history, and specific clay minerals may prove valuable in the treatment of bacterial diseases."

The researchers found that specific clay mineral products have antibacterial properties which have potential to treat numerous human bacterial infections.

Reference
Haydel SE, CM Remenih, and LB Williams. 2008. broad-spectrum in vitro antibacterial activities of clay minerals against antibiotic-susceptible and antibiotic-resistant bacterial pathogens. J. Antimicrob. Chemother. 61: 353-361.

Soil pollution and human health

People living in areas with fertile soils are better nourished than those living in degraded soils due to the higher quantity and quality of food in the former than the latter. Likewise, people living in polluted environments are more exposed to the ill effects of pollutants. The paths of environmental contaminants leading to humans are the following (Logan, 2000):

a) Soilàcropàhuman

b) Soilàlivestockàhuman

c) Soilàcropàlivestockàhuman

d) Soilàsurface watersàfishàhuman

e) Soilàgroundwateràhuman

f) Soilàairàhuman

g) Soilàhuman

The pathways a to e are indirect links between soil and human health and are relatively well-known. The pathways f and g are direct links and are little known and understood.

Direct links between soils and human health is geophagy

Humans ingest soil either involuntarily or deliberately. For the involuntary ingestion, every person ingests at least small quantities of soil. This is because any soil adhering to the skin of fingers may be inadvertently taken in by hand-to-mouth activity. This is especially true for children who like to play outdoors and for people working outside buildings or in the fields. Soil is also an important constituent of household dust and many foods such as fruits, vegetables and tubers crops usually contain some soil particles especially in poor countries. It is estimated that an average adult ingests soil at a rate of 10 mg per day.

Geophagy is the deliberate ingestion of soil by humans and animals. It is practiced by different peoples in all continents but is most common in the tropics particularly in Africa. This phenomenon was already known in the ancient world but the first detailed scientific report about it was written by the great German naturalist and founder of geography Alexander von Humboldt during his expedition of 1799-1804 to South America. Von Humboldt observed that eating soil was practiced by the indigenous Ottomac people in the Orinoco in Venezuela. The reasons for geophagy are still being debated until now but are known to vary from place to place. These include: soil as famine food to appease the pangs of hunger, as medicine and therapeutic (recent research has shown that clay adsorbs and detoxifies toxins and has antimicrobial action), cravings and good taste especially for pregnant women, as source of mineral nutrients to correct deficiencies, and an abnormal appetite for non-food substances. But excessive soil intake can lead to death of an individual due to the toxic effects of some mineral elements like Fe. This is likely to happen if the soil is contaminated with pollutants. Ingesting soil can also cause ingestion of eggs of parasitic worms and other disease-causing organisms (Abrahams, 2002; Dominy et al., 2004).

Another direct link between soil and human health occurs through inhalation. People inhale soil dusts inside their houses and by just walking in the street. The amount of inhaled dusts under normal conditions is generally low and thus is not harmful. But very dusty environments can cause lung problems. Also inhalation of even small amounts of the fibrous dust of serpentine and amphibole minerals commercially called asbestos is dangerous in that it can cause diseases and even cancer.

References

Abrahams, P.W. 2002. Soils: their implications to human health. The Science of the Total Environment 291: 1-32.

Dominy N.J., E. Davoust, and M. Minekus. 2004. Adaptive function of soil consumption: an in vitro study modeling the human stomach and small intestine. Journal of Experimental Biology 207: 319-324.

Logan, T.J. 2000. Soils and environmental quality. In: Handbook of Soil Science (M.E. Sumner, ed.). CRC Press, Boca Raton, pp: G155-G169.