By Claudia LeeFeatures correspondent

Pesticides are widely used worldwide to boost plant growth. Although effective, they contain toxic chemicals that can seriously impair our senses and nervous system.

Fifteen years ago, Tim Parton, a farm manager at Brewood Park Farm in Staffordshire in the UK, decided to take a leap and start to experiment with biological farming. Instead of using synthetic pesticides and fertilisers, he applies self-brewed biologically active natural inputs, such as trichoderma, a type of fungus, onto his crops, to help them both grow and fix nitrogen and phosphorus into the soil. 

Parton is part of a growing farming community practising regenerative agriculture. Regenerative agriculture is an approach to farming that prioritises soil and environmental health by minimising synthetic inputs.

He switched to using biologically active inputs after experiencing headaches and skin rashes from using pesticides. After sheep dipping, which involves immersing sheep in insecticide and pesticide mixtures to eliminate parasites, lumps would often show up on his arms. The reaction would stay for several days. "I would be a mess, but if I went to the doctors, they would say 'you've just had a reaction' and would not take it seriously," he says.

Since adopting a biological farming method, Parton has not experienced any negative health impacts. He has not had to use any phosphorus and potassium fertilisers on his crops for over 10 years. "I try to keep the plant as nutritionally balanced as I can, and if the plant has got all the correct nutrition, it doesn't get ill," he says.

He says he has observed a big increase in insect and bird species since he stopped using pesticides to control insects and weeds. "The knock-on effect is that I've got more bird numbers here than I should have, lots of threatened species are multiplying here because the food source is here," he says.

Pesticides are substances or chemicals used to repel, destroy and control pests, weeds or other organisms that affect plant growth. Although effective, pesticides contain toxic chemicals that can have wide-ranging, and sometimes chronic, effects on human's sensory organs and nervous system.

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First deployed in the 1930s to protect crops in the US, many agricultural communities soon became dependent on their use because of their dramatic effect on yields. Today, around one-third of the world's agricultural products are pesticide dependent.

According to the World Health Organization (WHO), over 1,000 types of pesticides are used globally, with some of the most common types being herbicides (49%), fungicides and bactericides (27%) and insecticides (19%).  In 1990, global pesticide consumption was at 3.72 billion lb (1.69 billion kg); this figure grew over 57% in the past two decades, reaching 5.86 billion lb (2.66 billion kg) by 2020.

A UN Environment Programme report forecasts continued growth in pesticide use. As the world's population is expected to reach 9.3 billion people by 2050, a 60% increase in the rate of food production is required. To sustain this demand, researchers believe farmers will need to use even more pesticides.

According to a study on European farming systems, omitting pesticides altogether can lead to a 78% loss of fruit production, a 54% decrease in vegetable harvests and a 32% loss of cereal yields. But our dependence on pesticides also comes at a significant cost to the environment, with research showing pesticides may be responsible for the loss of smell in honeybees and salmon, and have contaminated water bodies, threatening aquatic ecosystems.

Pesticides can also enter the food chain, through a process known as bioaccumulation. This occurs when a substance builds up in the body due to our inability to break it down. Since many synthetic pesticides cannot be broken down by animals or humans, they may end up bioaccumulating in body fat.

This can have a detrimental impact on human health. Despite global regulations on pesticide use, one study estimates that about 385 million cases of unintentional, acute pesticide poisoning occur among farm workers each year.

When sprayed, pesticides produce vapours that may turn into air pollutants. In the US, 37-54% of pesticide-related illnesses among agricultural workers are attributed to spray drifts; symptoms can range from headaches and nausea to burning sensations on the skin.

What are the most common insecticides?

Organophosphates and pyrethroids are the top two most used insecticides in the US; both chemicals are neurotoxic to animals. Insecticides are designed to interfere with the nervous system of target species, creating a chemical imbalance that prevents the normal transmission of nerve impulses. However, insecticides can have neurotoxic effects on non-target species as well. Insecticide use has also led to the widespread contamination of aquatic environments.

Early symptoms of pesticide exposure can include headaches, nausea, dizziness and respiratory secretion, says Michelle Perro, a former paediatrician who co-founded the non-profit GMO Science, a public platform where physicians discuss and analyse the impact of genetically engineered crops and foods. Acute health impacts can range from seizures to respiratory depression. The mode and length of exposure and the type of pesticide used all affect its impact on our sensory and nervous systems. "Exposure by inhaling pesticides through our lungs can be more toxic, because our gut contains microbes that help to detoxify pollutants," says Perro.

Pesticide exposure has also been linked to sensory deterioration. One of the earliest known incidences occurred in the 1960s in Japan's Saku agricultural region. Residents of the region were found to have a high incidence of visual defects after exposure to organophosphates. The effect of Saku disease included blurring of vision, eye movement disorders, myopia and astigmatism. A study of the residents in the area found that aside from farmers, the wives of farmers, who may have been exposed via take-home contamination or spray drift from nearby fields, also suffered from decreased visual acuity and loss of vision.

"When pesticide applicators have pesticide residues on their skin or clothing, those around them can inhale these residues – extended secondary exposure can also lead to harmful effects on health," says Honglei Chen, a professor of epidemiology and biostatistics at Michigan State University.

Chen is part of a 2019 Michigan State University study investigating the effect of pesticide exposure on olfactory functioning. The study monitored 11,232 farmers over a period of 20 years. Of the studied farmers, 10.6% experienced a high pesticide exposure event (HPEE). A HPEE is not officially defined and is dependent on the farmers' interpretation of the severity of their pesticide exposure. Farmers with a history of HPEE had a 49% higher chance of having a poor sense of smell.

A 2020 study found that of the estimated 860 million agricultural workers worldwide, 44% are affected by pesticide poisoning annually. This is due to a lack of protective equipment or defective equipment, which increases exposure through skin absorption, inhalation or ingestion. "When pesticides enter the body through inhalation, [they] bypass our blood brain barrier and impair nerve function," says Chen. "Alternatively, [pesticides] can enter our bloodstream through our gastrointestinal tract if ingested."

Many studies also establish a link between pesticide use and neurodegenerative diseases. Pesticide exposure has been associated with conditions such as attention deficit hyperactivity disorder (ADHD) and Parkinson's disease. A study from the University of Guelph in Canada suggests that pesticides cause animal cells to mutate in a way that mimics the effects of mutations which are known to cause Parkinson's. In another study pyrethroid pesticides were found to cause increased DAT (dopamine transporter expression) in mice.  DAT is a type of gene expression also observed in individuals with ADHD.  Exposure to pesticides during pregnancy or early life has also been associated with the development of autism among children.

What are the most common herbicides?

In the EU, the most common class of pesticides are fungicides and bactericides (45%), followed by herbicides (32%) and insecticides and acaricides (11%). Two of the most common herbicides include atrazine and glyphosate. Both substances are used to control weeds and grasses, and are often applied on common crops such as soybean, corn and sugarcane. 

Because they are designed to target an organism's nervous tissue, insecticides such as organophosphates, carbamates and organochlorine pesticides are more toxic than herbicides. Although there is strong evidence that acute, high-quantity exposure can lead to nervous system damage, it is still being studied whether chronic, moderate exposure has the same impact. Chen says that establishing a clear causal link between pesticides and deteriorating health remains a challenge because "there are many environmental toxins in the atmosphere, such as air pollutants, viruses and volatile organic compounds…these can all build up in the body and cause a cumulative adverse health effect".

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From the microplastics sprayed on farmland to the noxious odours released by sewage plants and the noise harming marine life, pollutants are seeping into every aspect of our existence. Sensory Overload explores the impact of pollution on all our senses and the long-term harm it is inflicting on humans and the natural world. Read some of the other stories from the series here:

Children are particularly vulnerable to pesticides because of their physiology, faster metabolic rate and behaviours. "Children are often closer to the ground because of their height, they also exhibit frequent hand-to-mouth activity, so they have a higher risk of accidentally ingesting pesticides compared to adults," says Perro. According to a paper published in the journal Environmental Toxicology, children risk absorbing higher doses of pesticides because of the greater intake of food or fluids per pound of body weight.

In 2014, schoolchildren experienced pesticide poisoning in France's Bordeaux region. In a primary school located near a vineyard, 23 schoolchildren experienced nausea, headaches and skin irritations after fungicides were sprayed in the vineyard. The case resulted in a €30,000 ($31,842/ £26,488) fine for the two vineyards involved, after a private lawsuit was filed by two French environmental associations Sepanso and Génération Futures.

Cases of children falling ill from pesticide exposure can be found around the globe, from Hawaii to New Zealand. In India, pesticide poisoning among children has been a significant public health issue for decades. A study documenting the impact of the agricultural pesticide ALP on children in rural northern India found that of the 30 children admitted into intensive care, 14 children did not survive pesticide poisoning. 

Elderly people are also particularly vulnerable due to their thinner skin, which increases risks of poisoning from dermal contact. As their organ functions deteriorate, the liver and kidneys may take longer to remove toxins, making it more likely for pesticides to accumulate in their bodies and cause physical or neurological damage.

Although pesticide poisoning is more likely during acute or chronic exposure, consumers are susceptible via accidental ingestion or dermal contact. It is not uncommon for pesticide residues to remain on fresh produce. In 2022, the US Environmental Working Group (EWG) found that over 70% of non-organic fresh produce contains residues of potentially harmful pesticides. In a 2020 European Food Safety Authority report of pesticide residues in food, it was found that 29.7% of produce contained one or more residues equal to or below permitted limits, while 1.7% exceeded the legal limit.

Based on data gathered by the WHO and Food Agriculture Organization, governments and intergovernmental bodies will set food standards and establish "maximum residue limits" for pesticides in different types of food.

Consumers may have limited control over the frequency and amount of pesticides applied on their food, but the negative effects can be mitigated by the basic act of washing and cleaning their skin or food following exposure. It is possible to reduce pesticide levels by 10-80% through cooking and processing methods such as blanching, boiling and frying. A 2022 comparative study found that washing with water or boiling is the most effective way to remove pesticide residue.

Certain regions and countries have placed bans on specific pesticides. In 1962, biologist Rachel Carson's book Silent Spring brought the adverse impacts of pesticides on the environment to the public eye. This led to a national environmental movement in the US, which instigated a ban on DDT, an insecticide commonly used in agriculture.

The 2001 Stockholm Convention on Persistent Organic Pollutants, signed by 90 countries, has also banned over 20 substances to protect the environment and safeguard human health. The substances, which include pesticides such as aldrin and DDT, were selected due to their toxicity, resistance to degradation and ability to bioaccumulate in animals and ecosystems.

However, there are also countries that legally require the use of specific pesticides to control disease outbreak in crops. In 2014, France's wine-producing region Burgundy fined a winemaker €500 ($531, £441) for disobeying government requirements to spray his organic vineyard with pesticides. The requirement was announced after Flavescene dorée, a vine disease, spread in the region.

As part of the EU's strategy to shift to a more sustainable food system, the European Commission has committed to halving both the use and risk of pesticides by 2030. But some agricultural communities still find this target insufficient. A group of agricultural workers and consumers have formed the "Save bees and farmers initiative", calling for an 80% reduction in pesticide use by 2030 and a complete phase out by 2035.

Success stories such as Parton's show that farming without synthetic inputs is possible. At the 2020 British Farming Awards, Parton was named 'Farm Innovator of the Year' for this no-till and biological approach.

Since replacing pesticides with nitrogen-fixing bacteria, he says his yields have remained the same or surpassed previous years. The farm saves £90,000 ($111,000) a year on pesticides compared to 10 years ago.

"Last century was the chemical century," he says. "This century is going to be the biological one because we cannot keep polluting the planet in which we live."

"I farm in the heartbeat of nature, creating a healthy ecosystem on the farm for generations to come," says Parton. "Together we can make the changes needed to heal the planet in which we live. There is no planet B."

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