The Role of Pesticides in Human Health

Pesticides can help support food availability and affordability, and therefore currently play a vital role in global food security, which in turn is crucial for human health and wellbeing. In addition, pesticides are an important tool in controlling vector-borne diseases affecting human health, such as malaria and dengue. Both pest pressure on crops and levels of vector-borne disease are expected to increase with climate change, to the detriment of human health. These pressures may result in an increased reliance on pesticides to combat their impacts.

Human Health Impacts of Pesticides

Pesticide use is contentious, as it can pose multiple substantial direct and indirect risks to human health and the environment. Globally, a large body of evidence shows that exposure to pesticides can cause negative health effects on most body systems. Importantly though, the severity of these health impacts is mediated by the type of pesticide, and the mode, duration, and level of exposure. Whilst a precautionary approach to pesticides and human health is wise, it is important not to conflate these risks across different routes and levels of exposure.

Exposure to pesticides may be direct, for example through farmer eye contact with spilled pesticide, or exposure to spray drift.  In the EU, the health risks associated with direct exposure to pesticides during their application at work (including farmers, gardeners, and groundskeepers) or in the home garden, are consistently more severe than those from indirect exposures such as consumption of pesticide residues in foods. Pesticide residues in foods in the EU are restricted and monitored, meaning they are a limited route of exposure. However, they may represent an exposure route that could have health effects in the long-term.

Pesticide Exposure in the Workforce

The health effects associated with direct occupational exposure range in severity and are illustrated here. Globally, human health risk from direct exposure to pesticides varies widely with differences in the regulation of their use and availability. Significant global health inequalities around pesticide use are evident in many low income countries, where effective regulation is limited and research into exposure is sparse. Programs to reduce this risk include bans on the most harmful pesticides, and attempts to ensure the availability and use of personal protective equipment and safety training for professional users.

A recent major systematic review estimated what proportion of farmers and other workers using pesticides suffer acute health impacts from pesticide exposure at least once annually. This estimate includes acute exposures producing mild symptoms, as well as those causing severe illness. The results suggest that around 47% of occupational pesticide users in Argentina, 54% in East Africa, and 65% in South Asia suffer symptoms annually. In comparison, in Europe, where relatively strict controls are in place, pesticide poisoning is less common. Here, the same review found an estimated 23% of UK farmers and 32% of Southern European farmers suffer symptoms annually, however the potential long-term health impacts of this are not well understood.

Indirect Pesticide Exposure

Typically lower-level, indirect exposure to pesticides can be through the consumption of pesticide residues in foods and water supplies, or the migration of air- or dust-borne pesticides into the homes of those living close to spraying. Whilst potentially widespread, the long-term, low-level nature of such exposures makes assessing their health impacts difficult. As a result, the dose-thresholds for illness and the long-term health outcomes from chronic pesticide exposure are not well understood.

This is in part because health outcomes can become apparent after some time, making it difficult to ascertain with certainty the cause of illness when individuals are exposed to a multitude of different compounds which might cause illness through their lives. In addition, it is unclear whether, and to what extent, exposure to mixtures of pesticides may be causing greater health risks compared to the sum of the risk of the single compounds, commonly referred to as “cocktail effects”.

Whist causality is difficult to prove in indirect exposure, there are strong associations between chronic occupational or residential exposure to certain pesticides, and poor health outcomes. These include cancers and neurological, immunological, and reproductive effects. In contrast, most current evidence suggests that the risks of dietary exposure are low. In countries and regions with more stringent controls, such as the EU, foods are tested against Maximum Residue Levels (MRLs). These are set below the level deemed to be safe for consumers.

Pesticides, the Environment and Human Health: Issues at the Intersection

It is well established that pesticides can produce environmental and ecological damage. Human health and wellbeing are intimately linked to the state of the environment. Damage by pesticides to non-target species, including pollinators, soil fauna and diverse microbial communities, can impact key ecosystems services which underpin human health and wellbeing. These can include soil health, food production and soil-water regulation in extreme weather events. 

Source: Tang et al. 2021, Nature Geoscience.

The map above illustrates (calculated as a Risk Score (RS)) of agricultural land to pesticide pollution globally, accounting for the environmental concentration of multiple commonly used pesticide residues and the ecological sensitivity of the area (see here for more detail). This demonstrates the pressures placed on ecosystems in different regions, particularly in Europe.

Whilst protecting food production from pests can support food security and thereby human health, protecting the biodiversity that supports food production is equally important. Calls have been made to update the joint United Nations Food and Agriculture Organisation (FAO) and World Health Organisation (WHO) register of highly hazardous pesticides to better account for the environmental and human health effects of pesticides.

SPRINT: Pesticides, Environment and Human Health

SPRINT is contributing to the comprehensive assessment of the risks and impacts of pesticides on the environment and human health in 10 European countries and Argentina. Our understanding of these impacts remains incomplete, with much uncertainty, making changing policy to reduce harm difficult.

Within the SPRINT study, urine, blood, faecal, and nasal samples have been taken from organic and non-organic farmers, their neighbours, and consumers (for more information click the link to see our interactive monitoring plan). These will be used along with samples of indoor and outdoor dust, wristband exposure analysis, questionnaire data and exposure modelling to better understand the impacts on human health of pesticide exposure.

We will use our findings from this in the development of improved regulatory tools and methods for assessing pesticide risks, and to work towards the adoption of innovative transition pathways for more sustainable plant protection.

Further reading:

Risk of pesticide pollution at the global scale.

https://www.nature.com/articles/s41561-021-00712-5

Selection of pesticides to reduce human and environmental health risks: a global guideline and minimum pesticides list.

https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(19)30266-9/fulltext

The global distribution of acute unintentional pesticide poisoning: estimations based on a systematic review.

https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-020-09939-0

The State of the World's Biodiversity for Food and Agriculture.

https://www.fao.org/documents/card/en/c/ca3129en/

Connecting global priorities: biodiversity and human health: a state of knowledge review.

https://www.who.int/publications/i/item/9789241508537