Effect of Organic P Forms and P Present in Inorganic Colloids on the Determination of Dissolved P in Environmental Samples by the Diffusive Gradient in Thin Films Technique, Ion Chromatography, and Colorimetry

Abstract

The speciation of P in environmental samples is operationally defined, since it depends on the analytical method used. In this study, we compared four methods to measure P in solution: ion chromatography (IC), the malachite green colorimetric method (CM), the diffusive gradient in thin films technique (DGT) and, for total dissolved P, optical inductively coupled plasma (ICP). These methods were compared on three sets of solutions (filtered over <0.45 μm): solutions with model organic P compounds, suspensions of synthesized inorganic Fe and Al colloids loaded with P, and environmental samples. The environmentally relevant organic P compounds were only marginally detected by CM and IC. Substantial fractions of certain organic P compounds contributed to the DGT measurement. Colorimetric analysis of DGT eluates detected in general less P than ICP analysis, indicating that these organic P compounds sorbed on the zero sink layer. Phosphorus associated with inorganic colloids was completely recovered by CM, but not by IC and least by DGT. Measurements on a wide set of 271 environmental samples (soil pore waters, groundwaters, and surface waters) suggest that surface water P is largely present as orthophosphate and phosphate sorbed onto inorganic colloids, whereas organic P contributes more in groundwaters.

Molecular Speciation of Phosphorus Present in Readily Dispersible Colloids from Agricultural Soils

“…For example, P associated with Fe (hydr) oxides (Fe-P) is sensitive to reducing conditions (Beauchemin et al, 2003), P sorbed on Al (hydr)oxides (Al-P) or calcium phosphate precipitates is likely to be more vulnerable to pH changes (Lindsay et al, 1989), and organic P (P o ) is more bioavailable (Li and Brett, 2013). To date, however, the speciation of P coll has been characterized very generally by the colorimetric method or inductively coupled plasma mass spectrometry coupled with different size-fractionated techniques (Hens and Merckx, 2001;Van Moorleghem et al, 2011;Henderson et al, 2012;Regelink et al, 2013). Molecular speciation of P coll should be addressed to understand the long-term fate and subsequent impact of soilderived P coll in aquatic systems.…”

Characterization of Colloidal Phosphorus Species in Drainage Waters from a Clay Soil Using Asymmetric Flow Field-Flow Fractionation

“…A wide variety of organic and inorganic P species can be present in environmental water samples (Van Moorleghem et al, 2011). For example, organic P species such as inositol hexa kis phosphate (phytic acid), deoxyribonucleic acids (DNA), and phospholipids were found in leachate waters (Espinosa et al, 1999; Toor et al, 2003) and water extracts from agricultural soils (Turner et al, 2002).…”

An in-depth assessment into simultaneous monitoring of dissolved reactive phosphorus (DRP) and low-molecular-weight organic phosphorus (LMWOP) in aquatic environments using diffusive gradients in thin films (DGT)

“…17 This equation implies that the linear slope of m as a function of time will be linearly proportional to the ambient concentration (c). 21 These ndings are strongly supported by a review of organic P sorption studies by Celi and Barberis. 19,20 The strong affinity of Fe-oxide for phosphate makes it a suitable adsorbent also for many LMWOP compounds.…”

“…20 Since organic phosphates and orthophosphate have similar adsorption/desorption chemistry (Chapter 1.2) it is fair to assume complete elusion. However, the study by Moorlegham et al 21 suggests that a few LMWOP compounds are susceptible to hydrolysis under strong acidic conditions (pH # 0). of the ester-bonds linking phosphate to the adenosine or inositol molecule) decomposing the organic compounds.…”