How pesticides impact human health (Signal)

In Europe, the use of high volumes of chemical pesticides in agriculture, forestry and non-agricultural settings (e.g. roads, railways and urban green areas) is a major source of pollution. Besides the well-documented ways in which chemical pesticides impact ecosystem services such as pollination, soil health and natural pest control, there have long been concerns about possible adverse effects to human health associated with exposure to these substances.  

While direct exposure usually occurs via handling pesticides (for domestic or professional use), the general population can be exposed through a variety of other sources, including food, drinking water, and contaminated outdoor and indoor air. Agricultural workers and people living close to agricultural areas are also likely to be particularly exposed to pesticide drift from fields, volatilisation, and soil erosion. 

Different pesticides have different modes of action — adverse effects on biological organisms — and may thus result in different health impacts. In general, exposure to chemical pesticides has been shown to cause both unintentional acute poisonings and several chronic health effects. This includes various types of cancers, neurological disorders and developmental delays, adverse impacts on fertility and reproduction, behavioural problems, and chronic respiratory diseases.   

Existing studies do not always distinguish which individual pesticides may be associated with a higher risk of a certain chronic disease. In many cases, adverse health effects have been linked to toxic pesticides now banned in Europe but which still persist in the environment, such as organochlorine insecticides or the herbicide atrazine. Nevertheless, at least some of the 450 active substances currently approved in the EU, as well as some only recently banned, have also been implicated. For example, there is strong evidence that early life exposure to commonly used pyrethroid insecticides may increase the risk of developing behavioural symptoms such as anxiety, while organophosphate insecticides have been linked to neurodevelopment disturbances. Both classes of pesticides are also suspected to be carcinogenic, among other possible health effects.  

Importantly, some active substances contained in pesticides have endocrine-disrupting properties, thus potentially affecting health even at low levels of exposure. Moreover, people are often exposed to mixtures of different pesticides and other chemicals, which can interact to produce combined effects — even when exposure to each compound may be considered individually ‘safe’ . Lastly, while regulatory risk assessment largely focuses on active substances, there is growing evidence that other compounds contained in chemical pesticides, such as co-formulants and adjuvants, may be toxic in their own right, or increase the toxic effects of the active substance.    

Human biomonitoring — the measurement of pollutant levels in the body fluids or tissues of an individual — could play an essential role in assessing the actual aggregate exposure of European residents to pesticides from different sources. The results could therefore help identify whether policies to reduce pesticide use are effective enough. There is presently no EU-wide requirement to monitor human exposure to chemical pesticides. As a result, it is not yet possible to estimate the burden of disease linked to current levels of exposure to all pesticides in Europe. A large-scale human biomonitoring survey, conducted between 2014 and 2021 as part of the European Human Biomonitoring Initiative (HBM4EU), started to fill this gap. It measured the internal exposure levels of children and adults to priority pesticides including pyrethroids, chlorpyrifos (an organophosphate insecticide that has been banned in the EU since 2020), and the herbicide glyphosate. Although quality-approved data are only available for a relatively small number of countries, the survey indicates possible widespread exposure across Europe. Some biomarkers for chlorpyrifos and pyrethroids were detected in over 90% of the samples. A separate HBM4EU study also revealed widespread exposure to pesticide mixtures, with up to 84% of samples collected among children and adults in five European countries found to contain residues of two or more different pesticides.   

Significant uncertainty persists in evaluating risks posed by current levels of exposure, due to the challenge of deriving widely-accepted guidance values to use in risk assessment. According to the assessments performed under HBM4EU, levels of exposure to HBM4EU priority pesticides such as pyrethroids and chlorpyrifos suggest a potential concern for adverse health effects, especially among highly-exposed children. While exposure to chlorpyrifos may have decreased since the HBM4EU surveys, as a result of its approval being withdrawn by the European Commission, total sales of pyrethroids have increased in Europe between 2012 and 2021.