# Ambient fine particulate matter exposure influences oxidative stress and glucocorticoid concentrations in captive Asian elephants in Thailand

## TL;DR

Air pollution in Thailand increases stress and DNA damage in captive Asian elephants, suggesting a need for better protection and monitoring.

## Contribution

This study is the first to link PM2.5 exposure to oxidative stress and stress hormones in captive Asian elephants.

## Key findings

- High PM2.5 exposure increased DNA damage and stress hormones by about 40% and 35%, respectively.
- Lipid peroxidation decreased under high PM2.5, indicating possible antioxidant responses.
- The strongest effects occurred when pollution increased from low to moderate levels.

## Abstract

Asian elephants, an iconic flagship species, are increasingly exposed to seasonal pollution and ambient fine particulate matter (PM2.5) due to land burning and regional air pollution across Northern Thailand. Unlike humans and domesticated animals, captive elephants often spend prolonged periods outdoors with minimal air quality or mitigation measures, yet the physiological consequences of chronic PM2.5 exposure remain poorly understood. This study investigated how daily PM2.5 levels affected oxidative stress and physiological stress biomarkers in Asian elephants involved in tourist activities in Thailand. A total of 27 elephants from seven tourist facilities in Northern Thailand were repeatedly sampled for serum 8-hydroxy-deoxyguanosine (8-OHdG, a marker of oxidative DNA damage), serum malondialdehyde (MDA, a marker of lipid peroxidation) and faecal glucocorticoid metabolites (fGCM, a marker of stress). Daily PM2.5 concentrations were classified into tertiles (low, moderate, high). Linear mixed-effects models were used to test associations between PM2.5 and each biomarker, with elephant ID and camp as random intercepts. Elephants exposed to high PM2.5 showed approximately 40% higher DNA damage and 35% higher stress hormone concentrations compared to low PM2.5 conditions. In contrast, lipid peroxidation concentrations were about 15% lower under high PM2.5 conditions, suggesting possible compensatory antioxidant responses. The strongest changes occurred when pollution increased from low to moderate levels, further increases produced smaller effects. These findings suggest that seasonal air pollution elevates stress hormones and triggers complex, at times counterintuitive, changes in oxidative biomarkers, likely due to physiological buffering in elephants, with potential health implications. Integrated multi-biomarker panels are therefore essential for accurately monitoring air quality impacts on captive megafauna. Proactive management should prioritize reducing exposure and providing nutritional support during peak pollution conditions to mitigate cumulative stress.