Microplastics as pathway-selective modulators rewire nitrogen cycling in coastal wetlands: Polymer identity outweighs concentration.

Polymer identity, especially PS and PP, more strongly influences nitrogen pathway shifts in coastal wetlands than microplastic concentration.

• Why it matters: Understanding how microplastics affect nitrogen cycling is crucial because coastal wetlands are key nitrogen sinks that prevent eutrophication, yet their response to pollution remains unclear.
• What they did: A field-based mesocosm experiment exposed sediments from tidal marshes to four common polymers at environmentally relevant concentrations, analyzing interactions among tidal level, polymer type, and concentration.
• The result: Polymer type predicted nitrogen pathway changes more than concentration, with PS and PP causing significant declines in nitrogen removal functions and a shift from gaseous nitrogen loss to ammonium retention, especially at intermediate concentrations.