13
PHOSPHORUS FERTILISER
inputs . The nutrient exists in many chemical forms ,
bound to iron minerals calcium compounds or organic
matter and those forms differ greatly in how stable they
are with some more prone to leakage than others To
understand how blooms keep returning it is not enough
to know how much phosphorus is present we also need
to know what form it is in and where
Seeing that chemistry directly is difficult The most
informative X ray signatures of phosphorus are low
energy at which photons are readily absorbed by air
water and even detector windows At the ESRF however
specialised beamlines such as ID21 have been developed
to work around these constraints probing phosphorus
concentrations and chemical speciation at the sub
micrometre scale , using spectroscopic techniques such as
X - ray fluorescence ( XRF ) and X - ray absorption near edge
structure ( XANES ) . And now , powered by the vastly
higher brilliance and coherence of the EBS at low energy ,
ID21 ’ s new nano - scanning X - ray microscope endstation
can map the chemical landscapes of phosphorus down to
200 nm resolution – offering new insights into one of the
world ’ s most persistent environmental problems .
“ The ID21 beamline currently offers the highest
spatial resolution for the analysis of phosphorus by sub -
micron XRF imaging and XANES in the world , ” says
Gabriel Sgarbiero Montanha , a postdoc working at ID21
on the sustainable use of fertilisers .
A recent ESRF study of phosphorus and iron in organic -
rich sediments shows exactly what this level of detail can
reveal . For years , iron addition has been tested in lakes –
and considered more widely in the Baltic and other water
bodies – as a potential way of locking up phosphorus to
prevent blooms , because iron and phosphorus readily
bind together in sediments . To understand its long -
term effects , Melanie Münch at Utrecht University
in the Netherlands and colleagues used ESRF X - ray
microscopy and spectroscopy at the ID21 beamline to
map , at micrometre scales , how iron and phosphorus are
paired in sediment samples from a treated lake ( Figure 1 ) .
They found that in the peaty sediments of the lake part
of the phosphorus was bound in iron – organic micro -
phases , which are more reactive than crystalline iron
precipitates and are responsible for temporal phosphorus
release from the sediments ( Environ . Sci . : Processes
Impacts 27 563 ) . In other words , adding iron does not
necessarily lock phosphorus away for good , but can lead to
the formation of a phosphorus pool in the sediment that
can be easily released . “ This shows that understanding
the long - term fate of added iron in sediments is necessary
to prevent counterproductive effects , ” says co - author
Thilo Behrends at Utrecht .
Behrends adds that ID21 was pivotal in the project
because its design allowed the group to perform X ray
spectroscopy at low energy at the phosphorus K edge
The possibility to work with a focused beam was
necessary as the different iron and phosphorus phases in
the sediments could not be unequivocally disentangled
in bulk analyses
The difficulty of locking away phosphorus in sediments
leads researchers to consider what can be done upstream
in the agricultural land itself Field studies show that
only around 12 of the phosphorus applied as fertiliser is
recovered by plants One Earth 7 1402 Even now where
fertiliser is being applied more sparingly the phosphorus
I M A G E C O N T A I N S M O D I F I E D C O P E R N I C U S S E N T I N E L D A T A ( 2 0 1 9 ) , P R O C E S S E D B Y E S A
4
“ ID21 ’ s new nano scanning X - ray
microscope endstation can map the
chemical landscapes of phosphorus
down to 200 nm resolution . ”
March 2026 ESRFnews