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Pesticides can affect the health of agricultural workers

With a rise in the use of pesticides in Brazil, rural workers are increasingly being exposed to short- and long-term health impacts

Farmer sprays insecticide on a field of crops in the São Paulo Metropolitan Area

Sean Sprague / Alamy / Fotoarena

Headaches, tachycardia, fatigue, dizziness, irritation of the mucous membranes, blurred vision, cramps. Approximately 90% of family farmers surveyed in São José do Ubá, Rio de Janeiro State, in 2014 and 2015, frequently suffered at least one of these symptoms, as well as others identified as resulting from acute pesticide poisoning. In addition to analyzing symptoms of acute and chronic poisoning in this community, the researchers who carried out the study, from the Department of Environmental Health of the School of Public Health at the University of São Paulo (FSP-USP), also examined the mental and respiratory health of the 78 participants. Almost half of them had between four and nine symptoms of acute intoxication and a quarter had more than four chronic symptoms, such as sleep disturbances, irritability, and difficulty concentrating and reasoning. The region was Rio de Janeiro’s second largest producer of tomatoes.

“Agrochemical applicators, who are usually men, and their assistants, who are usually women, are exposed to high levels of these substances from a very young age,” said the study designer Rafael Buralli, a doctor of public health from USP. The research resulted in four scientific articles and was the subject of Buralli’s doctoral thesis. He is now a technical consultant for the Occupational Health Surveillance Department of Brazil’s Ministry of Health. When asked which agrochemicals they used, the farmers cited 49 different pesticides from 31 chemical groups—some of which are prohibited for tomato cultivation and one that is outright banned in Brazil.

According to scholars of the subject, acute agricultural pesticide poisoning, which caused 61 of the deaths recorded in the country by the National Toxic-Pharmacological Information System (SINITOX) in 2017, is only the most visible side of the health impacts on people directly exposed to pesticides. In 2017, the most recent year for which data is available from the system, 2,548 cases of acute intoxication were recorded.

Acute pesticide intoxication is manifested through clinical signs and symptoms of the harmful effects of interacting with the products in individuals responsible for handling them and applying them to crops. It presents suddenly, shortly after exposure to the chemical agent. Chronic intoxication, meanwhile, results from regular exposure to pesticides over months or years.

The Office for Social Communication at the Brazilian Ministry of Agriculture, Livestock, and Food Supply (MAPA) issued a statement declaring that not all of the deaths recorded by SINITOX in 2017 can be attributed to the misuse of pesticides, since 29 were suicides, two were reported as accidents, and others occurred in “unknown circumstances,” meaning the cause of death was not recorded.

Reginaldo Minaré, deputy technical director of the Brazilian Confederation of Agriculture and Livestock (CNA), acknowledges that pesticides are dangerous chemicals that “need to be handled with care.” But he stresses that considering the sheer volume applied nationwide, workers are “actually quite well protected.”

“We prepare farmers and provide technical assistance to make sure they properly use these substances, which are essential to Brazilian agriculture,” he says. Minaré highlights that the National Agricultural Learning Service (SENAR) has trained more than 200,000 rural workers to use pesticides over the last decade—15 million people are employed in agricultural establishments across the country, according to the 2017 Agro Census by the Brazilian Institute of Geography and Statistics (IBGE). The CNA director points out that awareness needs to be raised about the correct use of equipment. “But I don’t see a lack of preparation among workers. We are heading towards an interesting level of safety.”

Last year, MAPA launched the National Training Program for Applicators of Agrochemicals and Related Products, also known as the Legal Applicator Program. “Training is mandatory for applicators to reduce the likelihood of poisoning,” said the agency.

Specialists studying the problem say that intoxication is severely underreported. The World Health Organization (WHO) estimates a global average of 50 unreported cases for each recorded event. In the 2021 book Desastres sócio-sanitário-ambientais do agronegócio e resistências agroecológicas no Brasil (Socio-sanitary-environmental agribusiness disasters and agroecological resistance in Brazil) by Wanderlei Antonio Pignati of the Department of Public Health at the Federal University of Mato Grosso (UFMT) and colleagues, a chapter on acute poisoning by agricultural pesticides in the state of Mato Grosso states that in some towns, such as Sapezal, cases were underreported by up to 100% over the three years observed. It is worth noting that it is mandatory for health professionals to report such cases.

Lelia Valduga / Getty ImagesAided by a tractor, a worker applies pesticide on a farm in Santa CatarinaLelia Valduga / Getty Images

“Even with underreporting, it is evident that the regions with the highest agricultural production—which obviously use pesticides the most—have the highest incidence of acute intoxication in agricultural workers,” says Pignati. Among them is the municipality of Sorriso, the largest producer of soybeans and corn in the country. These crops, in addition to rice, cotton, and pasture areas, had the highest rates of agricultural pesticide poisoning in the workplace, the researchers wrote in the book. Soybean alone accounted for 31% of cases in Mato Grosso between 2007 and 2016. In 2015, it accounted for 63% of pesticides used in the state, which uses more agrochemicals than any other state in Brazil.

Scientists point out that despite being the most easily identifiable part of the problem, acute intoxications are not the cause of the biggest impact on human health as a result of direct and continuous contact with pesticides. They stress that exposure to pesticides in small, regular doses can lead to chronic health conditions. The correlation between these two factors (long-term exposure to pesticides and the emergence of chronic diseases), however, is much more difficult to study and prove. In some cases, diseases appear years or decades after exposure. The issue is growing in importance as the use of these substances rises year on year in the country.

According to the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA), 162,400 tons of active ingredients for pesticides were sold in Brazil in 2000. The volume jumped to 383,500 tons in 2010 and 686,300 tons in 2020. The top selling active ingredient, by far, is the herbicide glyphosate.

Data from the United Nations Food and Agriculture Organization (FAO) places Brazil as second only to the USA in the total volume of pesticides used in 2020. In terms of the volume used per area of cropland, the country is in 26th place, according to FAO data. This statistic, according to experts, more accurately reflects the use of agrochemicals in a given country.

José Otávio Machado Menten, a retired professor at USP’s Luiz de Queiroz College of Agriculture (ESALQ) in Piracicaba, emphasizes that chemical products such as fertilizers and pesticides are essential to the national agricultural sector. “Without the use of agrochemicals, Brazil would not be the agricultural powerhouse it is. Our projections indicate that national production would fall by half if we did not use pesticides,” he says.

For Menten, agrochemicals are safe substances subject to rigorous approval processes that involve not only agronomic aspects, but also environmental and toxicological studies. “The acute toxicity of agricultural pesticides is variable. If properly applied, even products with a higher acute toxicity do not pose a risk to worker health or generate unacceptable residues in the food produced.”

In the scientific literature, pesticides have also been associated with the development of cancers—including prostate cancer, non-Hodgkin lymphoma, leukemia, and cutaneous melanoma—problems with the reproductive system, neurological diseases, mental illnesses, endocrine alterations, cardiovascular complications, and dyslipidemia, which is an imbalance in cholesterol and triglyceride levels.

“The term pesticide covers a world of possibilities. It’s not like asbestos, which we know is a single substance that causes disease and death,” explains Cleber Cremonese, a biologist from the Institute of Collective Health at the Federal University of Bahia (UFBA) “The challenge for science is to find evidence of an association between so many substances—with different chemical structures and mechanisms of action—which are usually used mixed together and the numerous possible outcomes.” Cremonese is primarily interested in the effects of pesticide exposure on reproductive health and the potential influence on kidney health.

He was one of the authors of an article published in the scientific journal Reproductive Toxicology in 2017 that presented data suggesting that chronic occupational exposure to modern pesticides can negatively affect semen quality in young farmers in southern Brazil. The study involved men aged 18–23 from Farroupilha, in Serra Gaúcha, where family farming focuses on fruit production, especially grapes.

The researchers noticed an inverse association between sperm morphology and motility and the use of pesticides, including fungicides, insecticides, and herbicides. “The greater the chronic exposure to pesticides, the lower the percentage of sperm with proper morphology and motility,” says Cremonese.

Scientific articles on workers at Rio Grande do Sul’s grape and tomato farms contribute to a set of evidence of possible health damage resulting from the use of and exposure to pesticides. According to the definition used by the Ministry of Health, exposure to pesticides includes anyone who comes into contact with them at work, at home, or accidentally.

In recent decades, scientific studies have led to the banning of pesticides made of organochlorine compounds, the most well-known of which is DDT, which was used on a large scale until the 1970s but was eventually banned from agricultural use in Brazil in 1985. These substances, classified as persistent organic pollutants (POPs) because they remain in the environment for such a long time, affect the central nervous system and can cause serious liver and kidney damage. They have also been associated with an increased risk of breast cancer and other types of tumors.

With organochlorides almost completely out of use, the so-called organophosphates, which are less persistent in the environment, have taken their place—such as acephate, malathion, chlorpyrifos and glyphosate, four of the top 10 best sellers in Brazil in 2020. Along with another group of pesticides called carbamates, organophosphates have caused episodes of acute poisoning and deaths from occupational exposure in Brazil, emphasizes Buralli in his thesis, defended in 2020.

Armando Meyer, a biologist from the Institute for Collective Health Studies at the Federal University of Rio de Janeiro (UFRJ) who studied the mechanisms of action of the insecticide chlorpyrifos and its effects on the central nervous system during his PhD, believes organophosphates were a “bad response” by the industry seeking to replace organochlorides.

“Organophosphates originate from very toxic molecules, much more so than organochlorides. It’s a shame that chlorpyrifos continues to be used in Brazil.” The substance is banned in 35 countries, including all of those in the European Union, and in 2021 the USA prohibited its use on any crops that produce food. It has been linked to neurodevelopmental problems and impaired brain function in children. The Brazilian Health Regulatory Agency (ANVISA) is currently reassessing its approval status in Brazil.

“Until the reassessment is complete, there is no definitive scientific position on the subject in Brazil,” emphasizes biologist Leonardo Braúna, technical advisor to the Brazilian Association of Soy Producers (Aprosoja Brasil). “Aprosoja knows that chlorpyrifos is important to agricultural management and that we must not jump to conclusions based on what other countries are doing.”

“For the agricultural sector, it is never good to remove an efficient and important pest control product,” says Minaré, from the CNA. “The decision to ban any product must have solid grounds.”

Meyer’s doctoral research on chlorpyrifos was carried out on animals, as are the studies presented by companies submitting a substance to government regulatory agencies seeking approval for use as a pesticide. Unlike new drugs, which aim to provide a beneficial therapeutic action, pesticides are biocides formulated to inactivate organisms, so they cannot be tested on humans.

“The industry therefore has to carry out a set of standardized toxicological tests on animals, and they cannot do clinical trials. But there are limitations to these tests. It is then left to us, public health researchers, to conduct observational studies,” says the biologist, referring to the analysis of data from populations already exposed to these substances.

Loren McIntyre / Alamy / FotoarenaOn large farms, pesticides can be applied by planesLoren McIntyre / Alamy / Fotoarena

A major challenge in toxicology is that rural workers and other groups are exposed to multiple pesticides, not just the one active ingredient tested by a given company. “It is common for workers to mix five or six products in the pump they carry on their backs, applying them together and exposing themselves to all of them at the same time,” says Buralli.

Meyer explains that there are three major sets of diseases covered by recurrent studies. The first is cancer. “For some cancers, there is lots of evidence. I am referring to blood cancers in general, such as leukemia and lymphoma, especially non-Hodgkin lymphoma. Then there are the gastrointestinal cancers,” says the scientist.

The second most studied side-effects are mental and neurological diseases. “The way these products kill insects is by disrupting their nervous functions—and humans still share biological similarities with these animals.” The third front is potential effects on reproductive health.

According to MAPA, no substance approved in Brazil has been proven to cause cancer or affect human semen quality. “The approval criteria for agrochemicals are hazard-based and do not consider risk assessment measures adopted in the rest of the world, such as occupational exposure, dose reduction, acceptable daily intake, etc. In this respect, Brazilian legislation is the most restrictive in the world,” said the agency.

Cohort studies
In the USA, much research on the impact of pesticides on the health of agricultural workers derives from a cohort study of more than 89,000 people from Iowa and North Carolina that began in 1993, including farmers, their wives, and pesticide applicators. Known as the Agricultural Health Study (AHS), it is funded by the country’s National Cancer Institute (NCI) and the National Institute of Environmental Health Sciences (NIEHS), in collaboration with the Environmental Protection Agency (EPA).

In cohort studies, participants with no specific disease of interest at the beginning of the project are classified as exposed or not exposed to a particular substance, then monitored over time for various outcomes, such as illness or death. It is thus possible to compare the different outcomes between exposed and non-exposed individuals over a period of time.

In Brazil, Henrique César Santejo Silveira of the Molecular Oncology Research Center at Hospital de Amor in the interior of São Paulo—formerly Barretos Cancer Hospital—is starting a large cohort study of agricultural workers. The project “Cancer and rural workers: A cohort study (the RUCAN study),” funded by the Ministry of Health, will recruit 2,198 agricultural workers and their family members from Barretos and São José do Rio Preto in São Paulo State. The study is expected to last for at least 15 years.

“The FAPESP-funded study, when finished, will be the most consistent research ever carried out on the interaction between pesticides and the human population. We will be able to see the outcomes, know how many of the participants developed cancer, which type of cancers were frequent, and whether they are linked to a particular pesticide or not,” says Silveira.

“I believe that in the future, the same thing that happened with cigarettes will happen with pesticides,” predicts Silveira, noting that in the past, numerous studies demonstrated the harm caused by tobacco and a series of measures were then adopted to discourage its use. “We need to carry out quality research on the use of pesticides to better elucidate the effects they have on humans,” says the scientist.

In recent years, numerous studies and initiatives have sought to identify alternatives to the intensive use of pesticides in Brazil, such as the cultivation of organic foods and agroforestry. The use of drones to apply pesticides is another approach that could reduce worker exposure to chemicals and has been growing in popularity (see Pesquisa FAPESP issue nº 283). There are also studies that aim to reduce the frequency and volume of pesticide application. Another important area of research focuses on biological control, which uses natural pest predators and parasites to keep crops healthy (see Pesquisa FAPESP issue nºs. 254 and 305), or disease and pest prediction models that try to anticipate crop problems, reducing the need for pesticides.

Controversial bill
Politicians discuss changes to the rules for using, marketing, and regulating pesticides

The Brazilian law on pesticides could be changed. Bill 1.459/2022 entered the Federal Senate in September, replacing Bill 6.299 of 2002, authored by then Senator Blairo Maggi, Minister of Agriculture, Livestock, and Food Supply from 2016 to 2018. Dubbed the Poison Bill by critics, if approved it will replace current legislation passed in 1989 and will bring sweeping changes to the rules for using, marketing, and regulating pesticides.

Backed by the rural caucus, primarily because it would accelerate the assessment and approval of new substances for agricultural use, the bill gives greater power to MAPA, which would assume the role of coordinating the approval process. This responsibility is currently shared between the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA) and the Brazilian Health Regulatory Agency (ANVISA).

While current legislation prohibits pesticides with carcinogenic (can cause cancer), mutagenic (can alter DNA), and teratogenic (can cause fetal malformations) characteristics, the new bill is less explicit, stating that products that “present an unacceptable risk to human beings or the environment” are banned in the country.

Reginaldo Minaré, deputy technical director of the Brazilian Confederation of Agriculture and Livestock (CNA), believes the new bill is overdue. “The agricultural sector’s dissatisfaction with the approval system, which is extremely slow, dates back to at least 2005,” he stresses. According to him, it takes around eight years on average for a new pesticide to be approved in Brazil.

For ANVISA, which is responsible for evaluating the toxicological aspects and the risks of occupational and dietary exposure to pesticides, Bill. 1.459 “weakens the regulation of pesticide products, especially the assessment of their impact on the health of people who eat the food products.”