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Water, the food chain and persistent pesticides

  • Water, the food chain and persistent pesticides

Though pesticides are meant to help manage pests and diseases, some linger in our environments long after use.

Such is the case with a special class of pesticides called organochlorines.

Organochlorines are chemicals adversely categorized by the UN Stockholm convention as persistent organic pollutants (POPs).

These are chemicals which once released into the environment, are difficult to degrade.

They therefore persist over decades in our water, soil or air leading to bio-accumulation after introduction into the food chain.


Their presence in environmental media such as the water and soil render them not only available for uptake by crops but present in circulating air and even possibly in our water.

Organochlorines could therefore possibly find their way into our bodies through the food we eat or the water we drink and since they don’t break down easily, they bio-accumulate in fatty tissues.

Though most of these pesticides are outlawed in nations like Kenya, some types such as lindane were banned as late as 2015 meaning that their residues still linger in the environment as we speak.

This is besides lindane being categorized as a class 1 carcinogen whose long term exposure increases the risk of development of non-hodgkin lymphoma, a rare type of cancer.

As such, a growing concern exists about the prevalence of fish farming especially in areas where these pesticides have before been applied.

Fish farming

Driven by the growth of a healthy conscious middle class, fish farming especially in non traditional areas has ballooned in Kenya.

Perhaps for most of us, the tasty tilapia type entices us especially when stewed or deep fried.

Since construction of most fish farms takes into account availability of water, not much is considered with regard to the quality of the water being used.

And this is where the problem lies because most fish farms are being set up in farmlands where pesticides have before been applied.

So when it rains, the water flows through soils loaded with pesticide residues as it drains into nearby fish ponds leading to bioaccumulation in fish ultimately consumed by unsuspecting customers.

Though the current levels in fish might be acceptable, the problem could be magnified by continuous fish consumption from such sources.

Bioaccumulation of such chemicals through the food chain poses a bigger danger especially where infants are concerned.

Due to their fatty nature, many organochlorine pesticides find their way into fatty tissues in the body possibly leading to their presence in milk.

It’s scary to think of the way the immune systems of infants could be compromised by a continuous supply of such toxins through mothers’ milk.

Besides, due to their chemical structure, some organochlorines are known to adhere strongly to soil particles exposing crops grown on such soils and probably ending up on our dinner tables.

But the mobility of organochlorines wouldn’t be significant if we don’t consider their adverse effects.


Not only is long term lindane exposure associated with cancer, but so does exposure to other organochlorines which have been considered in several studies.

For example, a study in Pakistan among breast cancer patients found a higher than normal concentration of several organochlorine pesticide residues in blood.

Other organochlorine related substances such as some dioxin variants and polychlorinated biphenyls (PCBs) are also adversely associated with carcinogenesis.

Dioxins are air pollutants introduced by indiscriminate burning of rubbish or fossil fuels whereas PCBs are industrial chemicals.

Besides their potential carcinogenicity, high organochlorine levels in the blood might also lead to health complications related to the reproductive system.

Indiscriminate circulation of such substances in the environment could be curbed in a number of ways.

Integrated pest management (IPM)

This is a framework of intervention methods for control of pests and diseases in farms.

Though the usage of chemical pesticides might still be possible, it only happens only as the last resort.

Pests and diseases are primarily controlled using mechanical means such as application of sticky traps or biological means such as introduction of a predatory species.

Naturally derived pesticides such as garlic water or neem extracts could also be used for fungal control.

IPM might not eliminate pesticide use but might reduce the amount of pesticide residues in the environment.

But besides curbing indiscriminate use, removal of pesticides from contaminated water is important especially for use in fish farming or drinking.

Activated carbon

Activated carbon is formed from exposing organic matter such as agricultural or food waste to high temperatures in the absence of oxygen and in the presence of an activating agent such as steam.

This results into a highly porous carbon based substance capable of trapping and removing pollutants such as pesticides from water.

Usage of activated carbon in fish ponds or water filters might help in curbing the levels of organochlorines thereby blocking them from the food chain.

Variation of diet

Eating different foods from different market sources is bound to reduce the risk of bioaccumulation.

Whether this could mean purchasing fish from different vendors, sourcing vegetables from different markets or even trying out new vegetable varieties, a change is always good as a rest.


The challenge organochlorine pesticides present to us is one which needs a long term approach in solving because of their persistent nature.

Their poor ability to degrade coupled with the health complications they carry make them a key subject of concern not only to the environmental conscious but the health conscious as well.

Originally posted on John Mmbaga's blog

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