Chemicals in the Food Chain

The Food Chain

Think of the food chain as a system of givers and takers. It all starts with the givers – plants and algae called primary producers that take water and carbon dioxide from the atmosphere, add a little sunshine in a process called photosynthesis, and turn it into solid organic matter. These guys are right at the bottom of the food chain, and even though they can be anything between a single cell algae that is only visible through the microscope to a giant tree, reaching over 100m in height, it is their common ability to turn air and water into organic matter that is the basis of all life on the planet.

Everyone else in the food chain, including us, are consumers. Consumers can be split into categories – you’ll know which one you are. First up are primary consumers, herbivores that eat only plants. Next come secondary consumers, who are carnivorous and eat the herbivores. They are followed by tertiary consumers, who eat other carnivores. We can’t forget omnivores, who eat both animals and plants. Humans are naturally omnivorous, but some of us tend towards the carnivorous side of the menu while others prefer the herbivore road. The tertiary consumers sit at the top of the food chain, and while this might look a pretty safe place to be, when it comes to the problem of chemicals in food they suffer the consequences of all the chemicals taken in by everything they eat, that their food eats, and that their food’s food eats – you get the idea? You can see where this is going …

Chemicals and toxins increase with every step of the food chain, because they bio-accumulate. The consumers nearer the top of the pyramid are exposed to everything their food has already absorbed and stored in their tissue.

Environmental toxins,  like the chemicals sprayed on food crops, are absorbed by the plants, the primary producers. The toxins we should be most concerned about are the fat-soluble ones, which includes a lot of common chlorinated pesticides and herbicides. Some of these might not target the plant specifically and may not cause any obvious damage, but they will still be present in the plant’s cells. Animals eating the plants (primary consumers) absorb and accumulate the chemicals in their fatty tissue, and any animal consuming that fatty tissue – a secondary consumer – will absorb the chemicals in even higher concentrations. While these chemicals may not kill the guys at the bottom of the food chain, the higher up the food chain a consumer sits, the greater its exposure to accumulative toxins. 

Tractor spraying pesticides on vegetable field. The use of agrochemicals is widespread in western agricultural practices.

A very worrying example is that of a group of biotoxins called PCBs – or PolyChlorinated Biphenyls, a group of persistent chemicals (chemicals that don’t easily break down) that were used in industrial applications as additives to lubricants, foams, fire retarders etc. So in this case we are not talking about agrochemicals and food chemicals, but the example is well documented and illustrates the effects caused in food chain bio-accumulation. PCBs were mostly banned in the late 1970s, but because they don’t easily break down and their concentration in the food chain continued to increase for many years. Significant amounts are still present in certain parts of the world today. PCBs are not water soluble, so they accumulate in sediments of rivers and eventually the oceans. The food they mostly accumulate in is one that is often regarded as super healthy – fish! Most fish species we humans like to eat – species like snapper, tuna or cod – are the large predators of the oceans, fish that eat other fish. Their prey is often already a predator in itself, just smaller, eating even smaller fish, or small crustaceans. Crustaceans themselves often feed on a diet of snails, algae, larvae of fish, and eggs of sedentary filter feeders like shell fish and coral. The accumulation of PCBs in the food chain starts with the filter feeders, who filter huge amounts of water, hundreds to thousands of litres per day and increases with every step of the food chain. For us at the top eating the large predator fish this is bad news. In certain societies, were fish plays a huge role in their diet, like the hunting Inuit of the Arctic circle, levels of PCBs up to 160 times the amount considered to be safe have been found in their fatty tissue and in breastmilk, rendering them technically hazardous waste. (Study on health outcomes of Inuit children exposed to PCBs).

For omnivorous humans, no matter whether you eat a little meat or a lot, exposure to chemicals used in the agricultural sector is almost universal and very difficult to avoid. Check out my post “You are what are you eat”.  It’s also made more dangerous as the chemicals accumulate in your fatty tissue over a lifetime and interfere with immune function and brain chemistry. 

The role of chemicals on our gut microbiome

As well as the detrimental effects of chemicals in the food chain on our own biology there is another really important aspect to consider – our microbiome. While controlled lab tests can’t exactly predict the behaviour of a chemical in the real world most chemicals involved in food production undergo fairly vigorous testing (whether that type of testing is sufficient or even theoretically the right one is another question though). One thing that is rarely, if ever, considered is the effect of such chemicals on the microbiome, the community of trillions of bacteria, viruses and fungi that live in and on us. The importance of a healthy microbiome is becoming more and more evident, as are the things causing it harm. It’s now emerging that many common food additives have adverse effects on the microbiome. The obvious case is preservatives, which are added to food to specifically reduce the growth of fungi and bacteria, but artificial sweeteners, emulsifiers and colours have now all been shown to alter the composition of the microbiome, resulting in a reduction of the diversity of species (Palmnas et al, 2014, Suez et al, 2014). 

Check out my previous posts to read up on this: ‘You are what you eat’ and ‘You are what your foods eat‘.

Microbial communities in the gut are extremely diverse. Thousands of different species have been identified by scientists. However many chemicals in our food and our environment harm bacteria and constant exposure can lead to a reduction in beneficial gut baceteria (source of photo: Dr. Emma Allen Vercoe, University of Guelph, Canada).

The reduction of microbial diversity in your gut might not worry you as much as, say, missing the bus or wondering what to cook for dinner, but it should.  Studies conducted in the last 10 or 15 years are producing more and more evidence that with a reduced diversity of microbes in our gut comes a plethora of diseases and disorders. From Irritable Bowel Disease, diabetes, obesity, ulcerative colitis, coeliac disease, to depression, anxiety and autism – patients with these diagnoses have all been shown to harbour a microbiota reduced in diversity or where certain groups of bacteria that are normally present in small numbers have now become dominant. (Herrera et al: An overview of Microbiota-Associated Gastrointestinal Diseases, in The Human Microbiome Handbook).  Since chemicals such as preservatives are specifically designed to reduce microbial growth, ingesting them on a constant basis is bound to have effects on our gut microbiota. Combine that with all the other chemicals in the food chain that may not be specifically produced to harm bacteria, but may nevertheless do so, add to this cocktail the odd dose of antibiotics, it is not a giant leap to assume that our gut microbiota is constantly being threatened.  It’s also no surprise that it’s in a different state to the microbiota of our ancestors, which did not have to deal with the chemical onslaught of modern times. 

Evolution is slower than revolution – since the Green Revolution our biology hasn’t been able to keep pace with the threats that are presented to our body every day. But it’s not too late to do something about it. One of the best and easiest things you can do things you can do is to eat organic food. It contains no harmful chemicals, and because it has been grown or farmed in a traditional way with nourished soil, it’s packed with nutrients. Organics benefit both your body and your world, reducing the amount of toxins you’re ingesting while supporting the farmers, growers, makers and bakers that follow organic principles and work in a sustainable way. 

Organics are important no matter where in the food chain you sit and moving to organic food and products is one small step that can have huge benefits to everyone and everything, right down to the smallest living things, your microbiome.


Toxins in Food Webs explains in more detail how toxins move through the marine food chain.

 What is in your food? New Zealand Food Safety Agency’s short introduction to the most common food additives and toxins.

2 thoughts

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s