Extremely polluting form of phosphorus neglected by research
most studies on phosphorus, a pollutant found in many waterbodies, have focused on its 'soluble and reactive' form. But other polluting forms of this element constitute 50-100 per cent of the phosphorus pool in some ecosystems, as per new research. The work challenges conventional theories about the extent of pollution in coastal estuaries and threatened ecosystems.
Extensive use of fertilisers has increased phosphorus pollution by 75 per cent in land and freshwater ecosystems, says P V Sundareshwar, the lead author on the research; Sundareshwar is a bio-geochemist at the South Dakota School of Mines and Technology, the us .
Previous studies have only looked at 'soluble and reactive' phosphorus, not focussing on the dozen or more phosphorus containing compounds that have been labelled as 'soluble and unreactive'. These include polyphosphates and inositol phosphates. They are called 'unreactive' because they do not react in standard techniques used to measure phosphorus, such as the molybdate blue reaction. Moreover, they are neglected because they are thought to be biologically unavailable.
But new applications of techniques such as 31P nuclear magnetic resonance (nmr) spectroscopy are allowing a finer characterisation of this fraction of the phosphorus pool. Sundareshwar used 31P nmr analysis to show that pyrophosphate can constitute more than 50 per cent of the phosphorus in the sediments of some coastal estuarines. He also found that soil microorganisms readily use pyrophosphate, implying that it is biologically available. Moreover, its accumulation in the coastal zones was directly related to human activities, such as industrial use and fertiliser runoff.
"The results suggest that the actual extent of bioavailable phosphorus accumulation in estuaries is unknown despite decades of research," Sundareshwar says. The finding is important because in some coastal zones, phosphorus availability can limit the growth of beneficial bacteria and create zones of low oxygen, even in the absence of nitrogen-driven algal blooms. This means that resource managers must abandon their current focus on nitrogen alone and work to curb both nitrogen and phosphorus pollution.
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