CANCER-CHECK: Food, Metals, Soil


Food stimulates our taste buds and delivers the nutrients our bodies so much need.

Also, it’s common knowledge that fruits and vegetables provide us with the nutrients, antioxidants and health benefits our bodies crave for helping us in combating a spectrum of lifestyle diseases.

But besides the range of benefits that accrue from such foods, the way they are cultivated matters because of the use of one key agricultural input.


Mineral fertilizers are a group of chemically concentrated substances useful for crop development.

First produced and commercialized in the west, they have developed into products that not only deliver bumper harvests but have enabled food security to become a reality in many western nations today.

It’s not surprising to find agrovet shops in developing nations selling different brands of mineral fertilizers going by names such as CAN, TSP or DAP manufactured by different companies.

Most of these brands carry a triple number tag such as 10:15:10 symbolising the percentage concentration of the three crop macronutrients: nitrogen, potassium and phosphorus.

Mineral fertilizers are important for crop development.

They are known to significantly increase crop yields over a short period of time.

In fact this is the main reason why there exists such a high demand for them with many farmers (especially in developing nations) employing them in their farms indiscriminately at times.

But at what costs?


Being one of the most under emphasised parameters, soil acidity is perhaps more important than we think if we take into consideration it’s implications on the food we eat.

Healthy soil, being a complex ecosystem maintains a delicate balance between it’s physicochemical and biological components, which is usually disturbed by application of mineral fertilizers.

Being chemicals themselves, mineral fertilizers might not immediately be absorbed by crops and so depending on prevailing circumstances, they may react further with chemical components in the soil.

These reactions lower the soil pH increasing soil acidity especially during application of phosphate based fertilizers.

Increase in soil acidity may seem a small matter taking into consideration the benefits mineral fertilizers bring to our fold.

To some extent, this is true especially when farming in less polluted soils using fertilizers with a low heavy metal concentration.

But not when cheap mineral fertilizers are employed repeatedly over the long haul.


Some phosphate fertilizers come cheap simply because of naturally occurring impurities such as cadmium, a toxic heavy metal.

But the challenge is not presented by these fertilizers but by nations which import such commodities for sale to their farmers who unknowingly use them over and over again.

Even in nations like Kenya, lobby groups with good intentions have been advocating for importation of such fertilizers and with a good reason: cadmium removal will automatically elevate their prices making them too expensive for farmers…a delicate trade off.

But the key question is far and beyond affordability

It’s about sustainability and more importantly it’s about the health of masses.

Whereas cadmium laced fertilizers may not seem a big deal even with long term use, realities on the ground such as increased soil acidity may tilt that balance and mobilize these toxins leading to uptake in food crops.

That cadmium is known to accumulate at a higher concentration in leafy vegetables and potatoes should concern us especially if these same food crops are cultivated in degraded soils using fertilizers laced with cadmium.

Cadmium doubles up as a kidney and bone toxin besides being categorized as a broad spectrum human carcinogen by reputable organizations such as the IARC (an arm of the WHO) and the National Cancer Institute of the USA.

Unknowingly, degraded farm soils may act as toxin conduits all the way to our dinner plates.

And this toxic train doesn’t stop with cadmium.

Several mineral fertilizer samples have been tested and found to have significant concentrations of other toxic metals such as lead, arsenic and chromium.

Imagine the kind of damage such fertilizers pose if used repeatedly over acidified soils.

Which begs the question:

What can be done to reverse this damage?


Organic additives to the soil such as compost reverse this damage in several ways.

Firstly, compost being a nutrient rich product of decomposition of rotting matter in the presence of air teems with useful microorganisms, chemical nutrients and has just the right physical texture to help build soil over time.

In other words, if mineral fertilizers are considered to be ‘fast food’ then compost could easily be categorised as a ‘balanced diet’ rich with benefits for your soil and crops.

Secondly, compost making maintains nutrient cycles often ignored by application of mineral fertilizers.

Problems such as eutrophication are common around farms heavily using mineral fertilizers simply due to the loss of nutrients such as phosphates and nitrates.

Composting enables retention of such nutrients in a beneficial mix improving on food production while at the same time being environmentally friendly.

Lastly, composting introduces the missing ingredients to degraded soils: microorganisms.

Being the single most important component of agriculturally functional soils, microorganisms bring life to lifeless soils.

Bacteria, fungi, nematodes, viruses among others are sustained by carbon sources such as humus, decaying plant matter leading to an explosion of soil nutrients that can sustain crops over the long haul.

But this soil carbon source could come from a practice that is fast gaining traction among sustainability advocates.


Conservation agriculture entails leaving crop residue on the soil after harvest leading to decomposition which feeds the soil with carbon.

It must be noted that using mineral fertilizers together with compost and plant matter helps the soil rebalance it’s components preventing it from becoming too acidic.

Conservation agriculture also helps in maintaining soil structure reducing erosion and fast soil degradation.

But soil acidity could be corrected in a number of other ways such as using lime which is a calcium containing salt or even biochar.


Soil acidity brought about by overuse of mineral fertilizers not only contributes to rapid soil degradation but could also act as a conduit of introduction of metallic toxins into our food.

Employing affordable ways of reducing these hazards not only helps rejuvenate our agricultural soils but also in protecting society against the toxic effects of heavy metals.

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