Is nitrogen fertilizer supercharging allergy-causing pollen?

Nitrogen-fertilized grasslands may produce six times more pollen than their unfertilized counterparts, suggests a study published in The Lancet Planetary Health. The study also suggests pollen from fertilized grasslands is more likely to trigger hay fever than pollen from unfertilized grasslands.

Over recent decades, the rate of pollen allergies has increased globally. One reason for this rise is thought to be atmospheric nitrogen pollutants affecting pollen and leading to an increased release of allergens; however, little research has looked at the impact of nitrogen fertilizers, a major source of environmental pollution, on pollen.

This study compared pollen samples from 25 nitrogen-fertilized and 25 non-fertilized grasslands in Belgium. The study found an average pollen count of 3.6 mg/m² for the fertilized grasslands—6.2 times higher than the unfertilized grasslands with 0.6 mg/m² of pollen.

The study also looked at how allergenic the pollen was by taking the blood of 20 people and exposing it to the pollen from the two types of grassland. When comparing the sensitivity of the participants’ immune cells (basophils), they found on average that they were five times more sensitive to the pollen from the fertilized grasslands than the unfertilized grassland.

The authors say to confirm the allergy response, further research should expose participants themselves to pollen and then study their immune response.

Authors say this study is the first to suggest a clear relationship between nitrogen fertilizer and pollen count and its ability to trigger allergies and that the findings highlight an urgent need for strategies to not only address nitrogen fertilizer’s impact on biodiversity and the environment, but also the human health impact posed by nitrogen pollution.