About one third of invertebrate pollinators, such as bees, face extinction globally. And the pesticides that are contributing to their declines are also impacting human reproduction and longevity. World Bee Day offers us an opportunity to think critically about the human health implications of the widespread, indiscriminate use of pesticides.
Unfortunately, research in this area is lacking. Modelled estimates published earlier this year suggest that 64% of global agricultural land is at risk of pesticide pollution. Yet we know very little about what pesticides, or the amount, people are exposed to. Many farmers are not even aware of the type of pesticides they are applying.
Only now are we beginning to scratch the surface of understanding the implications of chronic exposure to these chemicals for human reproductive health and their association with increased risk of some of the leading causes of death including diabetes and cancer.
Latest evidence
One of the biggest concerns when it comes to chronic exposure to pesticides is that some of them are endocrine-disrupting chemicals or EDCs. Pesticides that are EDCs interfere with the functioning of natural hormones in our body such as estrogen and testosterone.
These disruptions to estrogen and testosterone have important implications for reproductive health. Studies, such as the Environment and Reproductive Health (EARTH) study at a fertility centre in Boston, have shown that men who consume more fruits and vegetables with higher levels of pesticides have poorer semen quality: 49% lower sperm counts, 32% lower percentage of normal sperm, and lower ejaculate volumes. In addition, women in this study who consumed more fruits and vegetables with high levels of pesticides were more likely to miscarry. Dr Jorge Chavarro at Harvard University, a researcher involved in the EARTH study, has said, “Consuming organically grown produce or avoiding produce known to have large amounts of [pesticide] residues may be the way to go.”
Reproductive epidemiologist at Mount Sinai in New York, Professor Shanna Swan’s new book, opens with the shocking statement, supported by her research, that, “We are half as fertile as our grandfathers were. And if the trend continues, we may very well reach a point where the human race is unable to reproduce itself.”
With respect to pregnancy outcomes, a study conducted by Dr Jaacks and Professor David Christiani at Harvard University found that pregnant women in Bangladesh with the highest levels of 4-nitrophenol in their urine – a marker of exposure to the pesticides parathion and methyl parathion – were more than three times more likely to deliver preterm and have a child that was small for gestational age compared to women with the lowest level of exposure.
Pesticides can impact foetal health. Credit: Unsplash.
Disrupting the normal function of our body’s hormones is not the only mechanism through which pesticides impact our health. Another class of pesticides, organophosphorus insecticides, kill insects – and humans who are exposed to high doses – by inhibiting an enzyme known as acetylcholinesterase. Acetylcholinesterase’s job in the body is to breakdown a common neurotransmitter, acetylcholine. Acetylcholine plays many different roles throughout the nervous system, including activating muscles, but also in attention and memory.
The chemical weapon, Sarin, a nerve agent, is also an organophosphorus compound. It is perhaps not surprising therefore that organophosphorus insecticides such as parathion are responsible for a significant number of premature deaths from pesticide suicide. A study by Dr Ayanthi Karunarathne and Professor Michael Eddleston at the Centre for Pesticide Suicide Prevention found that, since the Green Revolution introduced these highly hazardous pesticides to the developing world, an estimated 15 million pesticide suicides have occurred.
In 2019, the FAO and WHO released a call for action, Detoxifying agriculture and health from highly hazardous pesticides, stating: “With adequate investment in scaling-up existing and new ecological alternatives for pest control, pesticides that pose unacceptable risk to humans and the environment can be phased out from agriculture and other use sectors.”
Lower-dose exposure to organophosphorus insecticides has also been shown to have negative effects on neurodevelopment. For example, a study conducted in Thailand by Professor Pornpimol Kongtip of Mahidol University and Professor Susan Woskie of the University of Massachusetts Lowell found that children born to pregnant women with higher levels of organophosphorus insecticide metabolites in their urine had lower cognitive and motor development scores using a ‘gold standard’ assessment method known as the Bayley Scales.
Reduced exposure
We know from randomized controlled feeding trials that eating organic foods – even if it is just organic fresh fruits and vegetables – can significantly reduce our exposure to pesticides. We also know from surveillance data in countries that routinely monitor pesticide residues that some fruits and vegetables tend to have higher levels of pesticides than others, for example, leafy green vegetables, berries, and fruits grown in orchards such as apples, peaches, and nectarines. So going organic especially for these particular fresh fruits and vegetables may help reduce your exposure.
Some fruits and vegetables tend to have higher levels of pesticides than others. Photo: Unsplash.
Unfortunately, there is not much evidence to support washing with water for reducing exposure, particularly for newer classes of pesticides such as neonicotinoids. Neonicotinoids are systemic, meaning that they are taken up and transported to all parts of the crop – so simply washing the outside won’t help. Cooking can help to reduce residues, but does not entirely eliminate them.
Pesticides and climate change
Whilst fertilizer accounts for the largest share of greenhouse gas emissions in the production of many crops, pesticides are estimated to account for 9-16% of emissions. At the same time, the IPCC concluded in their 2019 Climate Change and Land report that there is high confidence “that agricultural pests and diseases have already responded to climate change resulting in both increase and decreases in infestations.” Crop protection will be critical to mitigate these risks, but there is no need for the same-old, highly hazardous, synthetic chemical-based approach.
Largescale transitions to organic agriculture without the use of synthetic fertilizer or pesticides are possible. Even under current nitrogen limitations, with concurrent changes in food supply and demand, 40-60% of global agricultural land could be converted to organic.
We need more government support for innovations in this sector to support these sustainable transitions. Demand for organics would also have to increase. Denmark is a leader in this regard, where organic produce makes up 12% of the food sales and 11% of agricultural land, both higher than the EU average. And the number of organic farmers and land converted to organic farming continues to grow year on year.
So, for those needing a little extra encouragement to get involved this World Bee Day, consider this: declining bee population health mirrors our own population health. We need to think carefully about releasing chemicals specifically designed to kill into the environment, and set up appropriate surveillance programmes to understand levels of exposure and resultant health effects for when we do.
Find out more about the Race to Zero and the Race to Resilience.
Professor Lindsay Jaacks featured in the fifth episode of the Royal Society of Medicine’s Health emergency of climate change series. Upcoming events include:
The unborn child and children’s health – Episode 6
Tuesday May 25 2021, 6:00pm to 7:00pm BST
Free, CPD accredited
Register today ➤
Mental health in a planetary crisis – Episode 7
Tuesday June 8 2021, 6:00pm to 7:00pm BST
Free, CPD accredited
Register today ➤
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