Pesticide exposure risks and seasonal variation in honey bee-collected pollen across agricultural landscapes in Latvia.

Honey bees (Apis mellifera) are widely used as bioindicators of environmental contamination and bee-collected pollen reflects pesticide exposure in agricultural landscapes. This study evaluated pesticide residues in honey bee-collected pollen from six Latvian apiaries during 2024 and 2025 flowering seasons, and assessed toxicological risk using the Pollen Hazard Quotient (PHQ). In total, 15 active substances were detected in 2024 and 19 in 2025. Fungicides were the most frequently detected pesticide class in both years, accounting for 51% of detections in 2024 and 54% in 2025, followed by herbicides (38% and 24%) and insecticides (11% and 22%). The highest concentrations were recorded for glyphosate, fluazifop-P-butyl, boscalid, azoxystrobin, acetamiprid, and tebuconazole. Seasonal variation was evident, with higher residue concentrations and PHQ values mainly from mid-May to early July, coinciding with crop flowering and pesticide application periods. Median PHQ values remained below the threshold (PHQ < 50), however several samples in 2025 exceeded this level, with a maximum PHQ of 1173.91 driven by cypermethrin. No consistent descriptive pattern was observed between PHQ values and the proportion of agricultural land or nectar producing crops. This suggests that landscape composition alone did not explain differences in pesticide exposure among the studied apiaries. The results indicate that pesticide exposure is influenced by temporal variation, pesticide toxicity, and local factors such as crop management and foraging behaviour, rather than landscape composition alone. Honey bee-collected pollen proved to be a suitable tool for monitoring pesticide exposure. It also allowed the identification of periods of increased risk in agricultural environments.