  Phosphorus (P) is an essential constituent of life but large P losses from
agroecosystems and sanitation systems are a major source of eutrophication in
water bodies.These losses are doubly detrimental as P in human excretions can
be used for crop fertilization.Through a unique dataset of 20,000 French
WasteWater Treatment Plants (WWTPs) operational measurements over two decades
and a P mass balance, we assess the fate of human excretions and their
agricultural potential.Despite 75% of French WWTPs sludge being spread on
crops, only 50% of the excreted P makes it back to agroecosystems. This is
among the highest rate in Western countries where assessments have been
made.Meanwhile, another 35% of the excreted P ends up in surface waters or the
environment through WWTP discharge, individual autonomous systems diffuse
losses, and sewers leaks.The remaining 15% is incinerated or sent to
landfills.Moreover, while WWTP removal efficiency increased in the 2000s,
reaching an 80% national average, it has been followed by a decade of
stagnation in every French basin.The final removal efficiency for each basin,
from 65% to 85%, closely matches whether the area was defined as P-sensitive in
the European directive.Our results suggest that recycling all P in excretions
could help supply 7 to 34% of French food supply without changing the current
food system.Reshaping agricultural systems (shifting to more plant-based diets,
decreasing P losses and food waste) would enable to go even further on the road
to food sufficiency.
