Chemical pesticides: A threat to soil, crops and human health

By Bharat Dogra 

A recent study by Prof. Rajni Yadav and Anand Narain Singh from the Soil Ecosystem and Restoration Ecology Lab of the Botany Department of Punjab University has drawn attention to the neglected issue of the great harm caused to soil microorganisms by chemical pesticides. Their research paper, titled 'Effects of Pesticides on Agriculture Essential Soil Microorganisms,' has been published in ACTA Scientific Agriculture. 

The paper states that the enhanced and indiscriminate use of chemical pesticides has led to the depletion of soil fertility, microbial population, and a reduction in crop production. After emphasizing that soil microorganisms play a vital role in maintaining soil health, ecosystem functions, and crop productivity, the paper recommends that it is essential to limit the use of conventional pesticides while increasing the use of bio-pesticides.

In the course of my numerous talks with farmers, I have found that the adverse impact of chemical pesticides on soil and the environment is generally well recognized by them. In particular, they relate chemical pesticides to the vanishing of earthworms from soil and express deep regret about this, as they recognize the selfless, ever-continuing service of earthworms in contributing to soil health.

There are some products whose adverse side-effects and hazards are so overwhelming that serious questions need to be raised about whether there are any net benefits — any proven benefits minus all the hazards, harms, and adverse impacts in the short and long term — of their continuing use. Various chemical pesticides together constitute one such product.

According to the Pesticide Action Network, which has been warning about the serious health hazards of chemical pesticides — particularly highly hazardous pesticides (HHPs) — for several years, there are an estimated 385 million unintended pesticide poisoning cases per year. Pesticides are also one of the most frequently used means of committing suicide. Apart from causing vomiting, fainting, and skin and other irritations, longer-term pesticide exposure has been linked to several serious health problems, including respiratory illness, cognitive impairment, neurological disease, organ damage, and cancer. In a recent US study involving not only farmers who actively use pesticides but communities as a whole, researchers contextualized cancer risk associated with pesticide use and smoking. They found that living in an environment heavily exposed to pesticides could increase the incidence of cancer by as much as smoking. The results were published in Frontiers in Cancer Control and Society.

"In our study we found that for some cancers, the effect of agricultural pesticide usage is comparable in magnitude to the effect of smoking," said the study's senior author, Dr. Isain Zapata, Associate Professor at Rocky Vista University, College of Osteopathic Medicine, Colorado.

The FAO and WHO have stated that the continued use of highly hazardous pesticides undermines the attainment of several Sustainable Development Goals (SDGs) because of their adverse impacts on health, food security, and biodiversity. Pesticides are known to be particularly harmful to invaluable pollinators such as bees.

The manufacture of many pesticides also involves very serious risks, as was alarmingly exposed during the Bhopal gas disaster of 1984, when thousands of people were killed by a poisonous gas leak and thousands more died due to longer-term impacts over the following years.

Pesticides have been required more in places where an artificial need for them was created by the mistaken growth of large monocultures of exotic seeds and crop varieties unsuitable for local conditions. Indigenous varieties — for example, of rice and cotton — that were not particularly susceptible to pests were abandoned on a large scale and replaced by exotic varieties that were highly susceptible. Had such costly mistakes, made under pressure from big business interests, been avoided, the need for chemical pesticides would have been far less.

I once asked a farmer from a tribal community practising mixed natural farming — growing about 30 crops on her small farm over the year — whether she loses some of her crop to pests. She said yes, but she was not too worried: cultivating her land, she accepts that some of the crop is for insects, some for birds, and most of it for her and her family. She said she had therefore never felt the need to use any chemical pesticide.

Pesticides have been linked to childhood cancers in a recent study that attracted considerable attention in the United States. These findings are also highly relevant in several developing countries, where lower awareness of hazards and precautions, as well as the prevalence of child labour, means children — including child workers — face a greater risk of close or direct contact with pesticides.

The study (2020), titled 'Childhood Cancer: Cross-Sector Strategies for Prevention,' was prepared by the Childhood Cancer Prevention Initiative (CCPI), USA. It argues that while childhood cancers are increasing rapidly, not enough attention has been given to prevention — particularly to reducing the environmental causes of cancer. In this context, the study emphasizes reducing exposure to carcinogenic and highly toxic substances, with special emphasis on highly hazardous chemicals, particularly chemical pesticides.

The study states: "Exposure to pesticides — the catch-all term for chemicals used to control insects (insecticides), weeds (herbicides) and fungi (fungicides) on crops and at home — has been implicated as a risk factor for leukemias, brain cancers and childhood lymphomas… A number of currently used pesticides are known or suspected carcinogens, according to evaluation by the International Agency for Research on Cancer (IARC) of the evidence for specific pesticides."

It is disturbing to learn that cancers can also be passed on to children from parents exposed to pesticides through their occupation. As the CCPI document notes: "Studies have examined associations between parental occupational exposure to pesticides and childhood leukemias and brain cancers. Maternal exposure during pregnancy is implicated in two meta-analyses examining links between chemicals and childhood leukemia; one of these found evidence linking leukemias with exposure to insecticides as well as herbicides. Both maternal and paternal exposures from working in the agricultural sector are associated with elevated rates of childhood brain tumours. It is important to note that the children exposed to high levels of agricultural pesticides are often low-income and immigrant children."

The study further notes: "In comparison to controls, elevated risks for childhood leukemia have been observed in children born to mothers who were exposed before conception and during pregnancy, and in children exposed after birth. For brain cancer, risks are elevated for children born to mothers exposed during pregnancy and children whose fathers were exposed prior to conception. For lymphoma, risks are strongest for children whose mothers were exposed during pregnancy."

The study has called upon pesticide manufacturers and promoters to heed cancer warnings, or else their own products and businesses will be harmed sooner or later due to growing public awareness. It states: "In early 2019, Bayer's stock value plummeted over 44% — a near seven-year low for the company — in the wake of yet another lawsuit finding that Bayer's recently acquired product, Roundup, was a cause of cancer. With over 13,000 claims focused on the carcinogenicity of glyphosate, the active ingredient in Roundup, investors were left wondering if Bayer's $63-billion acquisition of Monsanto in 2018 was worth the financial risk."

Pointing to the seriousness of the problem, the study notes: "Three primary pathways expose pregnant women, babies, and children to pesticides: parental work in agriculture; food and beverage consumption; and insect and weed control in residential, work, education and care facilities. The Centers for Disease Control and Prevention have found that 90% of Americans have pesticides in their blood and urine, and parental exposure to insecticides and herbicides is linked to childhood cancer."

Finally, the study makes the following policy recommendations:

- Require that government facilities and all early care and learning settings implement biologically-based Integrated Pest Management (IPM) strategies to minimize the use of chemicals in pest control.

- Protect families from residential pesticides; ban the open-market sale of pesticides that are carcinogenic or neurotoxic.

- Establish tight limits on acceptable levels of pesticides in final food products.

- Ban chemical pesticides for ornamental uses.

- Keep new pesticides off the market; prohibit approval of new pesticides until proven safe.

The findings of this study are highly relevant for developing countries, where risks of occupational exposure to pesticides are higher and several child workers directly handle pesticides. As childhood cancers continue to rise in many developing countries, these nations need to give adequate attention to the warnings and policy recommendations of this study.

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The writer is Honorary Convener, Campaign to Save Earth. His books include Protecting Earth for Children, What Our Children Will Inherit, A Day in 2071, and India's Quest for Sustainable Farming and Healthy Food