Climate change fuelling harmful pesticide use

Farmer spraying a farm
A farmer spraying his farm. Copyright: S. Kilungu (CCAFS), CC BY-NC-SA 2.0

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  • Researchers assessed how cotton smallholders are adapting to climate change
  • They found increased pesticides use as a strategy for improving resilience
  • The pesticides could increase risk of miscarriage among women farmers, expert says

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[NAIROBI] Smallholder farmers are increasingly using a group of pesticides that are harmful to humans to adapt to climate change, making the need to ban the manufacture, trade and use of these chemicals urgent, a study has found.

The pesticides commonly used by farmers in Zimbabwe and other parts of Sub-Saharan Africa belong to a group of chemicals called endocrine disruptor compounds (EDCs), and include dichlorodiphenyltrichloroethane (DDT), an insecticide banned decades ago by the US.

Pesticides, according to a report by the Africa Development Bank Group, are often toxic to humans. They can contribute to increased risks such as neurological, respiratory, immunologic and reproductive health problems as well as cancer, immune system damage and other sickness in the short term.

“Harmful encounters with pesticides can occur in a number of situations. Most directly, farmers or other agricultural laborers applying these chemicals to crops risk contact via exposed skin and eyes, both of which can absorb chemicals at potentially toxic levels, or through ingestion via the mouth and nose,” the report adds.

“Climate change is increasing farmers’ use of, and exposure to these pesticides.”

Cliff Zinyemba, University of Zimbabwe

The research published in the International Journal of Environmental Research and Public Health last month assessed the relationship between climate change and human health. It looked at the role of climate change in worsening existing health risks associated with exposure to pesticides that disrupt the endocrine system, a series of glands that produce and release chemicals used by the body for essential functions.

“Climate change is increasing farmers’ use of, and exposure to these pesticides. Climate change is resulting in increases in pest populations and the appearance of new pests in agriculture,” says Cliff Zinyemba, the study’s lead author and a lecturer in environmental and occupational health at the University of Zimbabwe.

Researchers assessed how pesticides affect the endocrine system by interviewing 50 Zimbabwean smallholder cotton farmers aged at least 30 years old on their climate change adaptation practices.

The study found that pesticides such as amitraz and endosulfan commonly used by Zimbabwean smallholder cotton farmers have some EDC properties.

“EDCs interfere with the function of hormones,” says Zinyemba. “Hormones are chemical messengers which travel throughout the body coordinating a range of complex bodily functions, including appetite, metabolism, blood pressure, heart rate, reproduction, growth, and development.”

Farmers are resorting to regular pesticide spraying, and are increasing the types of pesticides used seasonally, the study adds. Many farmers are adapting to a shorter growing season by abandoning the practice of destroying and burning cotton stalks after harvesting to control pests and diseases.

“By maintaining the crop from the previous season, farmers have a chance of harvesting something during those seasons when the rains come late,” explains Zinyemba. “However, the major disadvantage of this practice is that crops from the previous season harbour a lot of pests and diseases previously exposed to pesticides. The result is that pesticides are now becoming ineffective as the pests have developed some resistance.”

According to the study, climate change increases farmers’ exposure to health risks from pesticides in many ways. For instance, when pesticides are used in hot weather conditions, they become more volatile and more toxic.

Farmers also change their practices in the field in response to warmer temperatures, adds Zinyemba. For example, drinking water while spraying which increases the risk of oral pesticide exposure.

Negative effects of endocrine disrupting chemicals, he explains, include an increased risk of miscarriage for pregnant women working on farms and problems relating to reproductive development of boys living on farms.

Zinyemba conducted the study while he was a doctoral student at the Centre for Environmental and Occupational Health Research, University of Cape Town, South Africa.
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Cromwel Lukorito, an agrometeorologist and a lecturer at Kenya’s University of Nairobi, says that recent evidence indicates that ECDs are detrimental to wildlife and humans.

“Because these substances do not decay easily, they may therefore, not be metabolised [broken down] or conversely, they may be broken down into more toxic compounds than the parent molecules,” he tells SciDev.Net.

Even substances from these chemical species that were banned decades ago, he explains, remain in high levels in the environment.

Endocrine disruptor pesticides, according to Lukorito, have also been shown to disrupt reproductive and sexual development in humans, and these effects seem to depend on several factors, including gender, age, diet and occupation.

“Age is a particularly sensitive factor. Human foetuses, infants and children show greater susceptibility than adults,” he explains.

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.