Nanosized plastics (nanoplastics)
releasing into the wastewater
may pose a potential threat to biological nitrogen removal. Constructed
wetland (CW), a wastewater treatment or shore buffer system, is an
important sink of nanoplastics, while it is unclear how nitrogen removal
in CWs occurs in response to nanoplastics. Here, we investigated the
effects of polystyrene (PS) nanoplastics (0, 10, and 1000 μg/L)
on nitrogen removal for 180 days in CWs. The results revealed that
total nitrogen removal efficiency decreased by 29.5–40.6%.
We found that PS penetrated the cell membrane and destroyed both membrane
integrity and reactive oxygen species balance. Furthermore, PS inhibited
microbial activity in vivo, including enzyme (ammonia
monooxygenase, nitrate reductase, and nitrite reductase) activities
and electron transport system activity (ETSA). These adverse effects,
accompanied by a decline in the relative abundance of nitrifiers (e.g., Nitrosomonas and Nitrospira) and denitrifiers
(e.g., Thauera and Zoogloea), directly
accounted for the strong deterioration observed in nitrogen removal.
The decline in leaf and root activities decreased nitrogen uptake
by plants, which is an important factor of deterioration in nitrogen
removal. Overall, our results imply that the presence of nanoplastics
in the aquatic environment is a hidden danger to the global nitrogen
cycle and should receive more attention.
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