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Expect More Exposure to Pests and Agricultural Chemicals as Climate Changes

Boxall ABA, A Hardy, S Beulke, T Boucard, L Burgin, PD Falloon, PM Haygarth, T Hutchinson, RS Kovats, G Leonardi, LS Levy, G Nichols, SA Parsons, L Potts, D Stone, E Topp, DB Turley, K Walsh, EMH Wellington and RJ Williams. Impacts of climate change on indirect human exposure to pathogens and chemicals from agriculture. Environmental Health Perspectives doi:10.1289/ehp.0800084
February 26, 2009

Synopsis by Heather Hamlin

Weather changes due to global climate change could substantially increase people's exposure to many pathogens and toxic agricultural contaminants, predicts a study from the United Kingdom. The full health implications are uncertain. Managing the risks will require research as well as policy changes.


Natural changes in climate usually occur slowly, unfolding over time scales that can be hundreds or thousands of years. The long spans allow plants and animals to adapt (Coenen et al. 2008). Even with slow changes, some organisms will not survive and will go extinct.

Humans can cause rapid environmental changes. Examples include deforestation, chemical pollution and development. These types of changes can be devastating to natural ecosystems and can even alter climate patterns.

Although many human activities contribute to climate change, the greatest impact may come from burning fossil fuels -- including gas, oil and coal. These fuels contain carbon, which is released into the atmosphere when the fuels burn. Carbon in the atmosphere has increased by 30 percent over the past century due to fossil fuel use, according to estimates.

Similar to how glass traps heat in a greenhouse, carbon and the other gases build in the atmosphere and trap the heat as it is re-radiated from Earth. This is why carbon is called a “greenhouse” gas and how it contributes to global warming.

Carbon is not the only culprit. Other activities add to climate change by releasing different types of greenhouse gases. Cattle and livestock, landfills, industrial activities and agricultural chemicals (such as some pesticides and fertilizers) can also trap heat.

Weather and climate regulate wind and water flow patterns. As climate change alters wind and water patterns, there will be significant effects on how chemicals and pathogens are distributed in the environment.

What did they do?

Researchers in the United Kingdom gathered data from scientific experts and published literature relating to the current use, distribution and human health effects of chemicals and pathogens associated with farming and raising livestock in Europe.

They then evaluated 1) aspects of climate change that could affect the movement of the pathogens and chemicals and 2) changes in how humans may be exposed through the environment -- air, water, food -- that would likely result from predicted changes in climate.

Using mathematical models, the scientists predicted the effects of climate change on many aspects of indirect environmental exposures associated with agriculture that are of concern to human health. The main agents were chemicals and pathogens, including pesticides, fertilizers, industrial pollutants (metals, dioxins, PCBs, etc.), biological pathogens (bacteria, viruses), pharmaceuticals, nutrients and allergens (mold, mildew, pollen, etc.).

What did they find?

Climate change is likely to alter the makeup of the chemical mix in the environment and may even change chemical forms. Higher temperatures may transform contaminants into either more or less harmful varieties. Some of these may be easier for organisms to accumulate.

Increases in the abundance of pests associated with agriculture are predicted, due in part to a reduced effectiveness of pesticides. This could lead to higher use of herbicides, insecticides, fungicides and medicines and the development of new types of chemicals and drugs to control the unwanted guests. The increased use of these pesticides will contribute to the growing list of human health concerns associated with pesticide exposure.

Hotter and drier/wetter conditions predicted by climate change may also influence current farming practices. Droughts may require more irrigation of fields and livestock. An excess of rain will flood fields.

Livestock may need to be housed indoors to reduce problems associated with exposure to temperature stress and waterlogged pastures. Raising animals indoors creates waste disposal problems. Close confinement raises the likelihood of disease through new and known pathogens. This may lead to increased use of biocides and veterinary medicines. In addition, workers will be in more frequent contact with the animals, leading to an increase in human disease transmission.

Climate change is likely to change how contaminants move through the environment. An increase in the frequency of heavy rainfall could result in flood waters flushing pollutants from holding ponds and previously undisturbed soils. The flushing could increase the contaminant load in food crops and food animals.

Stronger winds, which are predicted in some areas, would blow sprayed chemicals and dust faster, perhaps farther and possibly to new places.

Tilling, harvesting and other farming techniques kick up significant amounts of dust. Hotter, drier weather could contribute to drier soil and more dust in the air. Dust is a significant transport pathway for small pathogens including bacteria, fungal spores, steroids and pesticides (Rogge et al. 2007).

The number and variety of vectors -- animals that carry disease and parasites -- are predicted to increase as the climate changes, possibly exposing people and animals to disease-causing bacteria, viruses and other pathogens. As the vectors move more, they could increase disease transmission.

For example, warmer temperatures will increase the number, lifespan and geographical distribution of mosquitoes. It may lead to higher infection rates and epidemics of malaria and other diseases. However, this risk could be offset by avoiding hot temperatures, including staying indoors in an air-conditioned environment.

Policy, research and monitoring could help manage these risks.

What does it mean?

Climate change is likely to alter people's health risks associated with disease and chemical exposure. The model used in this study predicts a vast and varied array of undesirable effects from pesticides, pathogens, nutrients and allergens.

Because of the magnitude of possible changes, the authors argue it is "important to recognise that agricultural systems are linked to the wider environment and the implications of changes in inputs to and from these must not be ignored."

Although many of these increased risks are significant and startling, the authors believe much can be done to prevent some of the impending problems and damage. Some of their recommendations include:

• Develop surveillance for the presence of pathogens in high-risk areas to greatly increase our awareness and treatment of problem areas.

• Update regulations and policies regularly in light of new scientific knowledge. Some countries are already developing policies to limit negative effects from climate change (Boston 2008). Significant time lags between new research findings and policy development will not be acceptable in a rapidly-changing environment.

• Develop models and data sets for chemical and disease pathways that have not been extensively studied. These include dust transport and flood immersion.


Boston, J. 2008. Developing a long-term climate change mitigation strategy. Political Science 60: 99-115.

Coenen, D, I Porzecanski and TL Crisman. 2008. Future directions in conservation and development: Incorporating the reality of climate change. Biodiversity(Ottawa) 9: 106-113.

Rogge, WF, PM Medeiros and BRT Simoneit. 2007. Organic marker compounds in surface soils of crop fields from the San Joaquin Valley fugitive dust characterization study. Atmospheric Environment 41:8183-8204