Pesticides in soya farming may be behind leukaemia deaths in Brazil

­­More children have died of leukaemia since large soya plantations have gradually replaced cattle farms in parts of Brazil, suggesting that pesticide exposure could be involved. However, the number of deaths is low and the exact cause hasn’t been determined.

Over the past two decades, parts of the Amazon have experienced a 20-fold expansion of soya farming, with previously cleared cow pastures converted into croplands. In the Cerrado, a vast savannah region which neighbours the Amazon, such farming has tripled.

Southern Brazil has a long-standing soya farming industry, with a transition in land use taking place more recently in the north and centre of the country. Brazil overall uses more pesticides than anywhere else.

While carrying out agricultural research in the Amazon, Marin Skidmore at the University of Illinois Urbana-Champaign heard local people talking about a recent rise in childhood cancers, with previous research linking pesticide exposure to childhood leukaemia. “I wanted to see whether this phenomenon that I was hearing about on the ground would really bear out in the data,” she says.

Skidmore and her colleagues collected information about deaths due to lymphoid leukaemia in children under 10 years old – who usually develop a form of the condition called acute lymphoblastic leukaemia (ALL) – between 2004 and 2019 in rural areas of the Cerrado and Amazon, covering about 1.75 million square kilometres.

Healthcare workers in these places don’t necessarily report all lymphoid leukaemia diagnoses to government databases, says Skidmore. The researchers therefore focused on deaths, which were well documented, she says.

They compared that information with data about land use and the location of people’s homes relative to water sources and paediatric oncology centres.

The team found that for every 10 per cent increase in land used for soya farming, there were an additional 0.4 lymphoid leukaemia-related deaths of children under 5 years old per 10,000 people and an additional 0.21 such deaths for children under 10 per 10,000 people. A statistical analysis indicates this wasn’t a chance finding.

Death rates were higher in areas more than 100 kilometres away from a paediatric oncology centre. This makes sense, since ALL in particular is “a highly treatable cancer”, says Skidmore.

Looking specifically at children who were born after the soya farming surge began in 2004, approximately half of the 226 deaths due to lymphoid leukaemia may not have occurred without the growth of that industry, she says.

Critically, the team found that lymphoid leukaemia-related death rates were especially associated with living downstream from a soya farm, which suggests the children, or their mothers during pregnancy, may have been consuming pesticide-laced water. Previous research has linked pesticide exposure during pregnancy to cancer in infants.

The results don’t prove that pesticides from soya farming caused the deaths, but “I buy it”, says Pablo Menéndez at the Josep Carreras Leukaemia Research Institute in Barcelona, Spain. Nevertheless, the number of lymphoid leukaemia-related deaths is very low overall, he says.

Chensheng (Alex) Lu at Southwest University in Chongqing, China, says that while the correlation between the deaths and the soya farming expansion seems clear, the cause isn’t definite.

If the results are confirmed in further research, this will underline the importance of government-regulated pesticide policies, says Skidmore. These could include training protocols for anyone applying pesticides and access to competent healthcare to ensure early diagnoses and accessible treatment, especially for rural populations, she says.

Agricultural intensification, via widespread pesticide use, is probably going to be part of global food security strategies, says Skidmore, who is “not advocating for a wholesale stop to these inputs”. “I think, safety first – making sure public health is taken care of as we see potentially more intensification happening in regions that are potentially under-resourced or haven’t seen these types of chemicals in the past,” she says.