Researchers have reported that soy expansion and the subsequent increase of pesticide use in Brazil’s Cerrado and Amazon biomes may correlate with an increased risk of mortality among pediatric patients with acute lymphoblastic leukemia (ALL). The study was published by Skidmore et al in Proceedings of the National Academy of Sciences (PNAS).
Over the past few decades, Brazil has become the world’s leading soybean producer as well as the leading consumer of pesticides. Despite concerns about potential public health consequences, little is known about the effects of pesticide exposure in the general population.
“The Brazilian Amazon region is undergoing a transition from low-input cattle production to intensified soy culture with high use of pesticides and herbicides. The expansion has happened really quickly, and it appears educational efforts and training for pesticide applicators didn’t match the growth in pesticide use. When not used properly, there are health implications,” explained lead study author Marin Skidmore, MSc, PhD, Assistant Professor in the Department of Agricultural and Consumer Economics at the College of Agricultural, Consumer, and Environmental Sciences at the University of Illinois Urbana-Champaign.
“As this transition was happening, there were documented cases of pesticide poisoning of agricultural workers and evidence of chemicals in the blood and urine samples of nonagricultural workers in the surrounding communities. This indicates that this rollout had happened in a potentially dangerous way that was leaving people exposed,” she emphasized.
Study Methods and Results
Researchers investigated the public health consequences of exposure to pesticides—focusing on pediatric patients and mortality from ALL—by drawing on data such as health outcomes, land use, surface water, and demographics in the Cerrado and Amazon biomes. The sample primarily consisted of areas that were classified as rural and had at least 25% of land cover in agriculture.
The researchers reported that soy production in the Cerrado area has tripled from 2000 to 2019, and in the Amazon region there was a 20-fold increase, from 0.25 to 5 million hectares. Aligned with increases in soy production, pesticide use in biomes also increased between 3- and 10-fold. Brazilian soy farmers applied pesticides at a rate 2.3-times higher per hectare than the United States.
“Our results show a significant relationship between Brazil’s soy expansion and [mortality among pediatric patients] from ALL in the region. [The] results suggest that about half of [these] deaths over a 10-year period may be linked to agricultural intensification and exposure to pesticides,” stressed Dr. Skidmore.
The researchers demonstrated that a 10–percentage point increase in soy production was associated with an additional 0.40 deaths from ALL in pediatric patients aged younger than 5 years and an additional 0.21 deaths in pediatric patients aged younger than 10 years per 10,000 population. In total, they estimated that among 226 reported deaths from ALL associated with pesticide exposure between 2008 and 2019, 54.4% (n = 123) of them were pediatric patients aged younger than 10 years.
The researchers noted that although the findings didn’t provide a direct, causal link between pesticide exposure and cancer mortality, their methods followed a number of steps to rule out other potential explanations. For instance, they found no correlations between ALL mortality and soy consumption, changes in socioeconomic status, or prevalence of crops with lower rates of pesticide applications. The researchers also investigated contamination of water sources as a primary method of pesticide exposure.
“We looked for evidence of pesticide application upstream, in the watershed that flows into a region, and we found it is related to leukemia outcomes in the downstream region. This indicates that pesticide runoff into surface water is a likely method of exposure. About 50% of the rural households in this region had a well or cistern at the time of the 2006 agricultural census, which left the other 50% reliant on surface water as a source of drinking water. If the surface water is contaminated, pesticides used in soy production upstream can reach children living downstream through waterways,” Dr. Skidmore suggested. “Our concern is that our results are only the tip of the iceberg. We measured one small, very precise outcome. Pesticide exposure may also result in nonfatal cases of leukemia, and there is a risk of impacts on the adult and teenage community,” she continued.
Despite being highly treatable, ALL requires access to quality medical care. In the entire Amazon region, the researchers identified only two high-complexity pediatric oncology centers; however, other facilities can also provide treatment. They found that the increase in observed ALL mortality among pediatric patients following soy expansion was limited to municipalities that were more than 100 km from a treatment center.
“Our results indicate that there are several ways to mitigate the relationship between pesticide exposure and ALL deaths. This includes training and education for agricultural workers, smart regulations for pesticide use, and access to health care. We certainly are not advocating for a wholesale stop of using these inputs. They are important and valuable technologies, but they need to be handled safely and with some checks in place,” Dr. Skidmore encouraged.
Brazil is currently developing a certification program that requires pesticide applicators to undergo safety training and education. Such programs exist in many countries—including the United States—where pesticide applicators are required to be licensed and participate in an annual pesticide safety education and testing program.
“I think there is a strong awareness that safe use of pesticides is what's best both for agricultural productivity and for the communities. This soy expansion and boom are in many ways a huge win for Brazil's economy. We want to highlight that when changes happen fast, there are risks associated with that, and this is not isolated to Brazil. There is a lot of focus on agricultural intensification for global food security around the world. We need to find a balance where we get the productive benefits while mitigating any potential risks. When there is rapid rollout of these technologies in a new region, often an underdeveloped or poor region, how do we ensure there are guardrails in place to prevent another case like this?” Dr. Skidmore concluded.
Disclosure: For full disclosures of the study authors, visit pnas.org.The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.