The inositol phosphates are a group of organic phosphorus compounds found widely in the natural environment, but that represent the greatest gap in our understanding of the global phosphorus cycle. They exist as inositols in various states of phosphorylation (bound to between one and six phosphate groups) and isomeric forms (e.g. myo, d-chiro, scyllo, neo), although myo-inositol hexakisphosphate is by far the most prevalent form in nature. In terrestrial environments, inositol phosphates are principally derived from plants and accumulate in soils to become the dominant class of organic phosphorus compounds. Inositol phosphates are also present in large amounts in aquatic environments, where they may contribute to eutrophication. Despite the prevalence of inositol phosphates in the environment, their cycling, mobility and bioavailability are poorly understood. This is largely related to analytical difficulties associated with the extraction, separation and detection of inositol phosphates in environmental samples. This review summarizes the current knowledge of inositol phosphates in the environment and the analytical techniques currently available for their detection in environmental samples. Recent advances in technology, such as the development of suitable chromatographic and capillary electrophoresis separation techniques, should help to elucidate some of the more pertinent questions regarding inositol phosphates in the natural environment.

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Summary Phosphorus (P) from soil can impair the water quality of streams and lakes. We have studied the forms and pathways of its movement from soil to water using 1‐ha plot lysimeters, managed as grazed grassland for 12 months in temperate South‐west England. The water flow through three pathways, namely (i) surface plus interflow to 30 cm (on undrained soil), (ii) surface plus interflow to 30 cm (on a mole and tile drained soil), and (iii) mole and tile drains (to 85 cm), were gauged. Samples of water from each path were treated with various combinations of 0.45‐μm filtration and sulphuric acid‐persulphate digestion and molybdate reaction, to determine the different forms of P. The total P (TP) concentration was greatest in the surface plus interflow to 30 cm paths (means 232 and 152 μg l–1), whereas the mean concentration in the drainage to 85 cm was 132 μg l–1. This reflects the substantial enrichment of the Olsen‐P extracts from the surface horizons, as extracts from the 0–2 cm layer were 10‐fold more than below 45 cm. In all paths, the dissolved P comprised the greatest proportion of the P transferred, with dissolved reactive P being the dominant form. Draining land reduced the transfer of TP by about 30% (≈ 1 kg–1 ha–1 year–1), because it can be sorbed as it flows through soil to drains. All these concentrations could cause eutrophication in surface waters.

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The transfer of P in water draining from agricultural land can contribute to eutrophication and the growth of toxic algae. Traditionally, research has focused on particulate P transfer in surface pathways, with transfer by subsurface pathways perceived as negligible. We investigated this by monitoring P in leachate draining through large‐scale monolith lysimeters (135 cm deep, 80 cm diam.) installed in a field site in southwest England. The lysimeters were taken from four grassland soil types with a range of textures (silty clay–sand) and extractable‐P contents (15–75 mg kg−1 NaHCO3 extractable P) and leachate was sampled over two drainage seasons. Export of total P was <0.5 kg ha−1 yr−1 for all soil types. Concentrations of total P in the leachate routinely exceeded 100 μg L−1 and remained relatively stable throughout the drainage season, except during the late spring period when maximum concentrations >200 μg L−1 were detected from all soil types. Physically, most of the leachate P was dissolved (<0.45 μm), although 21 to 46% occurred in the particulate (>0.45 μm) size fraction, most notably from the sandy‐textured soils. Chemically, the leachate was dominated by reactive (inorganic) P from all soil types (62–71%), although a large proportion was in unreactive (organic) P forms (29–38%). Reactive P occurred mainly in the <0.45 μm fraction, while unreactive P was predominantly in the >0.45 fraction. Unreactive P in the <0.45 μm fraction was greatest during the springtime (April–May), probably reflecting microbiological turnover and release of P in the soil. Our results indicate that (i) subsurface P transfer from soil to surface water can occur at concentrations that could cause eutrophication and (ii) unreactive and >0.45 μm P forms are important in subsurface P transfer.