PM2.5 Pollution's Hidden Threat: Ammonium Nitrate Impacts Children's Learning Abilities

Exposure to ammonium nitrate, a key component of PM2.5 pollution and a product of agricultural emissions, has been found to affect learning ability and memory in children, according to a new study. 

The chemical is formed when ammonia gas, released from agricultural activities, reacts with nitric acid produced after burning fossil fuels. 

Previous studies have found ammonium nitrate to heighten the risk of ageing-related conditions such as Alzheimer's and dementia, in which cognition and memory is affected, suggesting that long-term exposure to PM2.5 can cause neurocognitive harm across one's lifespan. 

A critical measure of air quality, PM2.5 is a mixture of dust, soot, organic compounds and metals, a particle of which is below 2.5 micrometres in diameter. It is known to travel deep into the lungs, from where it can enter the bloodstream and then pass through the highly selective blood-brain barrier, thereby causing serious health problems. 

In a 2020 study, a team including researchers from the University of Southern California (USC), US, looked at PM2.5 as a whole and found no potential impact on children's cognition. 

However, this study, conducted by the same team and published in the journal Environmental Health Perspectives, analysed 15 chemicals constituting PM2.5 and thus, ammonium nitrate emerged as a "prime suspect". 

Based on residential addresses of nearly 8,600 children, aged 9–11 years, from across the country, the researchers used spatio-temporal models to analyse yearly levels of exposure to PM2.5 components. 

"No matter how we examined it, on its own or with other pollutants, the most robust finding was that ammonium nitrate particles were linked to poorer learning and memory. That suggests that overall PM2.5 is one thing, but for cognition, it's a mixture effect of what you're exposed to," study author Megan Herting, a professor of population and public health sciences at USC, said. 

Further, "understanding these nuances is crucial for informing air quality regulations and understanding long-term neurocognitive effects," Herting said. 

The study added to mounting evidence that has shown PM2.5 pollution to be detrimental to memory and cognition for people of all ages. 

"Mixture modelling revealed cumulative negative associations between chemical components of PM2.5 and children's cognitive performance across all three cognitive domains, with the greatest contributions from ammonium, nitrates, potassium, silicon, and calcium," the authors wrote. 

"Building upon a decade of research suggesting that PM2.5 exposure is detrimental to cognition, this work links childhood exposure to PM2.5 source mixtures to individual differences in cognition at 9-10 years of age," they wrote. 

This study's participants came from the ongoing Adolescent Brain Cognitive Development Study, tracking brain development and mental health of nearly 12,000 children and adolescents across the US.