Children with leukaemia who were exposed to pesticides during pregnancy or shortly after birth face sharply higher death risks, with rodenticides posing the greatest threat, according to a new study published in the journal Cancers.

Children breastfed for more than six months showed no increased pesticide-related mortality.

Children with leukaemia who were exposed to pesticides during their mother’s pregnancy or shortly after birth face a significantly higher risk of death during childhood, according to a new peer-reviewed study.

The results highlight that “exposures in the home environment, even before a child is born, may have lasting effects on survival after a leukaemia diagnosis,” Dr Lena Winestone, a paediatric haematologist-oncologist at UCSF Benioff Children’s Hospitals and one of the study’s co-authors, said in a news release about the study.

“While more research is needed, the findings underscore the importance of reducing children’s exposure to harmful pesticides whenever possible,” she said.

The federally funded study, published in the journal Cancers, examined the impact of pesticides on childhood leukaemia survival rates. The authors – seven California-based researchers – said previous studies have linked pesticides to the onset of childhood leukaemia, but survival rates have not been analysed.

The researchers examined medical data from 837 children diagnosed with acute lymphoblastic leukaemia (ALL) – cancer of the blood and bone marrow, which progresses rapidly – and interviewed the children’s parents about their residential use of 12 types of pesticides during three critical pre- and post-pregnancy developmental periods.

The study showed that 108 ALL cases resulted in death within five years of diagnosis. Pesticide exposure during pregnancy was linked to a 60 per cent higher risk of death, and exposure to rodenticides — one of the 12 types of pesticides studied – led to a 91 per cent increased risk of death.

Insecticides and herbicides were also linked to a higher risk of death, though to a lesser extent than rodenticides.

Children who were breastfed for more than six months did not face an increased mortality risk from exposure to pesticides, while children breastfed for less than six months faced “higher pesticide-related survival risks,” the authors said.

About 92 per cent of children studied were exposed to at least one type of pesticide during the three critical developmental periods studied. This shows “how widespread these toxic chemicals are in homes and environments where children live,” the researchers said in a statement.

Karl Jablonowski, senior research scientist at Children’s Health Defence, said the findings, “if reproduced and verified, are beyond black-box warnings.” He added: “If correct, no person who is pregnant, or may become pregnant, absolutely should ever come into contact with brodifacoum. That is an absolute, beyond individual discretion.

“People who use the rodenticide cannot know the pregnancy status of everyone is at risk of exposure. Pregnant women, sometimes unaware of their pregnancy for several weeks, cannot know of rodenticide contamination. Rodents go everywhere. The poisons we use against them go everywhere they go.”

While rodenticides were broadly associated with posing the greatest risk to children with leukaemia, Jablonowski said the study examined only one type of rodenticide, brodifacoum.

Brodifacoum is “a chemical that disrupts vitamin K recycling and kills rodents by depriving them of vitamin K, which is much needed to maintain the integrity of blood vessels,” Jablonowski said. However, failing to include other rodenticides was an “unsatisfactory element” of the study, he said.

“Since only one rodenticide was studied, there is no comparator. The authors must therefore convince the readers that rodenticide is the associated factor and not the conditions for which rodenticide is used,” Jablonowski said.

While the study included controls for the participants’ sociodemographic factors, he said this “does not control for the presence or absence of rodents or the conditions that lead to the presence or absence of rodents.”

Despite this limitation, if the study’s conclusions are verified in future research, they will shed light on a crucial risk factor for pregnant women, expectant parents and households, and young children, Jablonowski said.

Paediatrician, Dr Michelle Perro, who was not involved in the study, noted that while ALL survival rates have “improved dramatically with modern therapy,” the study’s results suggest that “disparities remain.”

“These data raise the issue that preventable environmental exposures around pregnancy should be one lever to further improve outcomes and narrow gaps,” Perro said.

The study’s authors noted that leukaemia is the most common cancer afflicting children in industrialised countries. Federal data show that leukaemia represents 25 per cent of all childhood cancer diagnoses, while ALL accounts for 78 per cent of all childhood leukaemia cases.

The authors cited several studies indicating “chronic low-level pesticide exposure, particularly from residential and occupational sources during pregnancy, is linked to higher childhood leukaemia risk.”

The researchers divided 12 pesticides into four broad categories: herbicides, insecticides, rodenticides and pesticides used for flea control. Exposure during pregnancy “was particularly impactful,” as “mortality was associated with exposure to both any pesticide category and rodenticides,” according to the study.

“These findings emphasise the vulnerability of pesticide-exposed patients, highlighting the impact of exposure prior to diagnosis,” the authors wrote.

Research shows there are several ways “household pesticides could worsen cancer outcomes,” Perro said, including “oxidative stress, immune dysregulation, endocrine effects, and co-exposures in formulated products.”

“Prenatal exposure could possibly prime the immune system and bone marrow in ways that impair responses to therapy or tolerance of treatment,” she said.

The researchers called for further study examining “mechanisms by which environmental exposures during key developmental stages may later impact cancer outcomes.”

Jablonowski said the study had some methodological shortcomings, including differentiating between the two main types of ALL – B-cell, which affects the body’s ability to produce antibodies, and T-cell, which affects cells that assist with the body’s ability to kill germs.

Perro acknowledged that the study contained methodological weaknesses, such as relying on parental recall to confirm the types of pesticides used during pregnancy, but emphasised the importance of the results. She said: “While we shouldn’t over-interpret a single study, the findings are consistent with other literature bridging perinatal toxic exposures to worse paediatric cancer outcomes.

“This work adds survival and not just the incidence to the list of child-health endpoints plausibly impacted by residential pesticides. It strengthens the case for clearer labelling, bans on residential rodenticides and public-health messaging that prioritises non-chemical pest control during pregnancy, which should extend to all ages of children.”

Other studies linking pesticides to poor health outcomes for children include: A study published in the New England Journal of Medicine in January concluded that exposure to toxic chemicals during childhood is a key driver of the chronic disease epidemic and the primary contributor to illness and death for children in the US.

A study published earlier this year in the journal Environmental Toxicology and Pharmacology found that children exposed to agricultural pesticides were at higher risk of experiencing cellular distress. A comprehensive literature review published last year in the journal Ecotoxicology and Environmental Safety identified a 41 per cent higher risk of miscarriage among women exposed to pesticides.

A study published earlier this year in the journal Ecotoxicology and Public Health detected 47 types of pesticides in dust, drinking water and urine samples from 81 households in Indiana.

Perro encouraged parents to avoid using all household pesticides, particularly rodenticides, “during preconception, pregnancy and early childhood,” and “to use integrated pest management instead.”

Last week, the White House released its Make America Healthy Again (MAHA) strategy report. The report states that the US Environmental Protection Agency (EPA), the US Department of Agriculture (USDA) and the National Institutes of Health will “develop a research and evaluation framework for cumulative exposure” to chemicals.

The EPA and USDA will also “launch a partnership with private-sector innovators” to encourage investment in “precision agriculture.” This includes “new approaches and technologies to allow even more targeted and precise pesticide applications” aimed at reducing “the total amount of pesticides needed” in agriculture.

However, the report drew fire from food safety advocates who said it did not go far enough in addressing the health harms of pesticides.

A study published earlier this year in the Journal of Agrarian Change found that increasing agricultural reliance on genetically modified crops has increased dependence on pesticides rather than reducing their use.

• A Tell Media report / By Dr Michael Nevradakis – a senior reporter for The Defender