Summary: Exposure to ammonium nitrate, a component of fine particulate pollution from agricultural emissions, is associated with reduced learning and memory in children. This type of pollution, also linked to neurodegenerative risks in adults, highlights how air quality impacts brain health across ages.

Fine particulate matter (PM2.5) penetrates deep into the lungs and can reach the brain, posing long-term risks. The study emphasizes the need for better understanding of specific pollutants and targeted air quality measures.

A new USC study involving 8,500 children from across the country reveals that a form of air pollution, largely the product of agricultural emissions, is linked to poor learning and memory performance in 9- and 10-year-olds.

The specific component of fine particle air pollution, or PM2.5, ammonium nitrate, is also implicated in Alzheimer's and dementia risk in adults, suggesting that PM2.5 may cause neurocognitive harm across the lifespan.

Ammonium nitrate forms when ammonia gas and nitric acid, produced by agricultural activities and fossil fuel combustion, respectively, react in the atmosphere.

The findings appear in Environmental Health Perspectives.

"Our study highlights the need for more detailed research on particulate matter sources and chemical components," said senior author Megan Herting, an associate professor of population and public health sciences at the Keck School of Medicine of USC.

"It suggests that understanding these nuances is crucial for informing air quality regulations and understanding long-term neurocognitive effects."

For the last several years, Herting has been working with data from the largest brain study across America, known as the Adolescent Brain Cognitive Development Study, or ABCD, to understand how PM2.5 may affect the brain.

PM2.5, a key indicator of air quality, is a mixture of dust, soot, organic compounds and metals that come in a range of particle sizes less than 2.5 micrometers in diameter. PM2.5 can travel deep into the lungs, where these particles can pass into the bloodstream, and bypass the blood-brain barrier, causing serious health problems.

Fossil fuel combustion is one of the largest sources of PM2.5, especially in urban areas, but sources like wildfires, agriculture, marine aerosols and chemical reactions are also important.

In 2020, Herting and her colleagues published a paper in which they looked at PM2.5 as a whole, and its potential impact on cognition in children, and did not find a relationship.

For this study, they used special statistical techniques to look at 15 chemical components in PM2.5 and their sources. That's when ammonium nitrate -- which is usually a result of agricultural and farming operations -- in the air appeared as a prime suspect.

"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," Herting said.

"That suggests that overall PM2.5 is one thing, but for cognition, it's a mixture effect of what you're exposed to."

For their next project, the researchers hope to look at how these mixtures and sources may map on to individual differences in brain phenotypes during child and adolescent development.

In addition to Herting, other study authors include Rima Habre, Kirthana Sukumaran, Katherine Bottenhorn, Jim Gauderman, Carlos Cardenas-Iniguez, Rob McConnell and Hedyeh Ahmadi, all of the Keck School of Medicine; Daniel A. Hackman of the USC Suzanne Dworak-Peck School of Social Work; Kiros Berhane of the Columbia University Mailman School of Public Health; Shermaine Abad of University of California, San Diego; and Joel Schwartz of the Harvard T.H. Chan School of Public Health.

Funding: The research was supported by grants from the National Institutes of Health [NIEHS R01ES032295, R01ES031074, P30ES007048] and the Environmental Protection Agency [RD 83587201, RD 83544101].

Author: Leigh Hopper

Source: USC

Contact: Leigh Hopper - USC

Image: The image is credited to Neuroscience News

Original Research: Open access.

"Associations between Fine Particulate Matter Components, Their Sources, and Cognitive Outcomes in Children Ages 9-10 Years Old from the United States" by Megan Herting et al. Environmental Health Perspectives

Abstract

Associations between Fine Particulate Matter Components, Their Sources, and Cognitive Outcomes in Children Ages 9-10 Years Old from the United States

Emerging literature suggests that fine particulate matter [with aerodynamic diameter ≤2.5μ⁢m (PM2.5)] air pollution and its components are linked to various neurodevelopmental outcomes. However, few studies have evaluated how PM2.5 component mixtures from distinct sources relate to cognitive outcomes in children.

This cross-sectional study investigated how ambient concentrations of PM2.5 component mixtures relate to neurocognitive performance in 9- to 10-year-old children, as well as explored potential source-specific effects of these associations, across the US.

Using spatiotemporal hybrid models, annual concentrations of 15 chemical components of PM2.5 were estimated based on the residential address of child participants from the Adolescent Brain Cognitive Development (ABCD) Study. General cognitive ability, executive function, and learning/memory scores were derived from the NIH Toolbox.

We applied positive matrix factorization to identify six major PM2.5 sources based on the 15 components, which included crustal, ammonium sulfate, biomass burning, traffic, ammonium nitrate, and industrial/residual fuel burning.

We then utilized weighted quantile sum (WQS) and linear regression models to investigate associations between PM2.5 components' mixture, their potential sources, and children's cognitive scores.

Mixture modeling revealed associations between cumulative exposure and worse cognitive performance across all three outcome domains, including shared overlap in detrimental effects driven by ammonium nitrates, silicon, and calcium.

Using the identified six sources of exposure, source-specific negative associations were identified between ammonium nitrates and learning & memory, traffic and executive function, and crustal and industrial mixtures and general cognitive ability.

Unexpected positive associations were also seen between traffic and general ability as well as biomass burning and executive function.

This work suggests nuanced associations between outdoor PM2.5 exposure and childhood cognitive performance, including important differences in cognition related both to individual chemicals as well as to specific sources of these exposures.