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Chemical speciation of arsenic species in human blood serum was performed by high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS) with direct sample inj...

A multiply hyphenated HPLC/UV/ICP-MS system equipped with a fraction collection valve for subsequent MALDI-TOF-MS analysis was constructed, and its applicability to the speciation of metalloprotein...

An octadecylsilyl silica (ODS) column coated with phosphatidylcholine (PC) was prepared by using a dynamic coating method, and its separation characteristics were evaluated for direct sample inject...

Assay of alkaline phosphatase (ALP) in salmon egg cell cytoplasm was performed by size exclusion chromatography (SEC) with fluorescence detection of enzymatic activity and element-selective detecti...

The concentrations of major-to-ultratrace elements in bittern, which was obtained after seawater concentration in the salt preparation process, were investigated by ICP-AES (inductively coupled pla...

The multielement determination of precious metals (Ru, Rh, Pd, Ir, Pt, and Au) in industrial waste incineration ashes was examined by inductively coupled plasma mass spectrometry (ICP-MS) with exte...

Chemical speciation of arsenic in human urine was performed by HPLC separation with ICP-MS detection in order to investigate the urinary excretion patterns of arsenic metabolites after one-time ingestion of an edible seaweed, hijiki (Hizikia fusiforme). A Japanese male volunteer ingested one serving of ca. 15 g (dry weight) of hijiki (containing ca. 0.9 mg of arsenic), and urine samples were collected at 3-5 h intervals for the following 3 days. As a result, different urinary excretion patterns were observed between inorganic and methylated arsenicals. Toxic inorganic As(V) and As(III) were detected in the urine 3 h after ingestion. The highest concentrations of As(V) and As(III) were observed at 6 and 15 h after ingestion, respectively. In contrast, methylated arsenic species in the urine, such as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AB), began to increase 10 h after ingestion and provided the highest concentrations at 21 h after ingestion. These results indicate that a large amount of As(V) from hijiki is excreted rapidly in urine and some part of it is reduced to As(III) in the human body. As(III) may then be converted to non-toxic methylated arsenic species and excreted in urine later than inorganic ones. It can be concluded from these experimental results that detoxification of arsenic occurs in the human body through the rapid urinary excretion of toxic arsenicals or by conversion to organic methylated ones after ingestion of hijiki.

A tandem preconcentration method using a chelating resin was exploited for simultaneous multielement determination of trace metals in seawater by inductively coupled plasma mass spectrometry (ICP-M...

A chelating resin-packed minicolumn was developed to pretreat seawater samples for the determination of trace metals by inductively coupled plasma mass spectrometry (ICP-MS). The preconcentration conditions, such as the flow rate of sample loading, pH for adsorption, amount of ammonium acetate for eliminating matrix elements, and the amount of nitric acid for eluting trace metals from the resin, were investigated and optimized. Firstly, 50 mL of seawater samples was adjusted to pH 6.0 and loaded into the column at the flow rate of 3 mL min - 1 . Secondly, 8 mL of 1 M ammonium acetate and 5 mL of pure water were passed through the column for eliminating matrix elements, such as Mg and Ca. Finally, trace metals were eluted with 2.25 mL of 2 M nitric acid, and then 0.25 mL of internal standard elements (Ge, In, Re, Tl, 100 μg L - 1 each) was added to the eluted solution in order to correct matrix effects in the ICP-MS measurements. The recoveries for 23 elements (Mn, Co, Ni, Cu, Zn, Y, Cd, all-REEs, Pb, and U) were more than 80%. The analytical results for the concentrations of trace metals in seawater reference material (NASS-5) agreed well with certified or reference values. The present method was also applied to the multielement analysis of the coastal seawater samples from the Take Island (Gamagoori, Aichi prefecture, Japan) and the Ise Bay (Nagoya, Aichi prefecture, Japan).

Coastal seawater and river water samples were collected near Nagoya port, located in the coastal area of the Ise Bay, and in six rivers around Nagoya City. The rare earth elements (REEs) in these samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) with chelating resin preconcentration. The concentrations of all REEs except for Pm in coastal seawater and river water samples could be determined at the concentration level from sub-ng L - 1 to 10 ngL - 1 . In order to examine the relative concentration variations, the REE patterns were estimated by normalizing the concentrations of REEs in the water samples to those in Post Archean Average Australian Shale (PAAS). Significantly positive Gd anomalies in the REE patterns were observed for river waters down from the urban areas as well as for coastal seawater. Such Gd anomalies were especially remarkable for river water collected near sewage treatment facilities in the Tenpaku river. It was, thus, concluded that the Gd anomalies in the REE patterns were artificially caused by anthropogenic sources mainly due to recent use of a gadolinium compound as a contrast reagent for magnetic resonance imaging (MRI) in medical diagnosis.

The leachabilities of major-to-ultratrace elements in industrial waste incineration fly ash (IWIFA) were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) in order to characterize IWIFA. The leaching data of about 50 elements in the IWIFA sample could be obtained in the concentration range from mg g-1 to sub-µg g-1, when HNO3 and aqua regia were used as the leachants. In addition, morphological observations of IWIFA particles were performed by a scanning electron microscope with an energy dispersive X-ray spectrometer (SEM-EDS) before and after the leaching treatment of the IWIFA samples. From the data for the leaching and morphological observations, the chemical states of the elements in IWIFA were elucidated as follows: (i) core materials of fly ashes were mostly composed of stable oxides of major elements such as Si, Al, Ti, and Fe; (ii) Cu, Zn, Mo, Cd, and Bi were mainly adsorbed on the surface of fly ash particles...

The multielement determination of major-to-ultratrace elements in industrial waste incineration bottom ash was carried out by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) after alkali fusion using LiBO2. The concentrations of 50 elements in bottom ash could be determined over the concentration range from 192 mg g−1 of Si to 0.072 μg g−1 of In. Silicon, Al, Fe, Ca, Na, and Ti, which except for Fe are lithophile elements, were major elements of industrial waste incineration bottom ash. The distributions of major-to-ultratrace elements in incineration bottom ash were evaluated by the enrichment factors. The enrichment factors of major elements in incineration bottom ash indicated that their relative contents were quite similar to those in the continental crust. It was also found that most minor and trace elements in the lithophile element group provided almost the same enrichment factors as those of major elements. On the other ha...

A tandem preconcentration method, in which chelating resin adsorption and La coprecipitation were cooperatively employed for preconcentration, was developed as a pretreatment method for simultaneous multielement determination of trace elements in seawater by ICP-MS. First, the seawater sample (250 ml) was treated with a chelating resin for preconcentration of trace elements, and then trace elements with good recoveries were determined by ICP-MS. Trace elements with the chemical properties of oxoanion- and hydride-formation, which were poorly recovered in the chelating resin preconcentration, were further subjected to preconcentration by La coprecipitation. As a result, more than 30 elements could be determined in the concentration range from 9.6 μg L-1 for Mo to 0.00018 μg L-1 for Tm, when the present tandem method was applied to the analysis of open seawater standard reference material (NASS-4). Furthermore, the analytical results for open seawater reference materials were compared with those for coastal...

The coastal seawater sample was filtered with a membrane filter (pore size 0.45 μm), and the filtrate was further filtered with an ultrafiltration filter (molecular weight permeation limit of 10000 Da). Then, major-to-ultratrace elements in the particles which remained on the membrane filter, the membrane-filtered seawater, and the ultrafiltered seawater were determined by ICP-AES (inductively coupled plasma atomic emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). From these analytical results, the fractional distributions of each element in the particle, large molecule and small molecule fractions of seawater were estimated, where the distributions of the elements in the large molecule fraction were obtained as the differences between the elemental concentrations in membrane-filtered and ultrafiltered seawaters. Furthermore, laboratory-made salts (Salts I—III) were prepared from original, membrane-filtered, and ultrafiltered seawaters. The concentrations of major-to-ultrat...

The simultaneous multielement determination of trace elements in seawater, especially hydride- and oxoanion-forming elements, has been investigated by inductively coupled plasma mass spectrometry with the aid of lanthanum coprecipitation preconcentration. The optimum pH in lanthanum coprecipitation was pH 9.5; at this value, trace elements were well recovered and major constituents of seawater such as Na, Mg, K, and Ca were significantly reduced in the concentrated solutions. The recovery values obtained for V, Cr(III), Mn, As(III), As(V), Se(IV), Y, Sn, Sb(III), Sb(V), W, Bi, and U were more than 85% after lanthanum coprecipitation, while Cr(VI), Se(VI), and Mo(VI) provided poor recoveries of less than 30%. The reproducibility for coprecipitation was within 5% as relative standard deviation. The present method was applied to the determination of trace elements in coastal seawater reference material CASS-3. The analytical values for Mn, As, V, Y, Sb, W, and U were in fairly good agreement with the certifi...

The multielement determination of trace elements in coastal seawater by inductively coupled plasma mass spectrometry has been investigated with the aid of chelating resin preconcentration. First, each coastal seawater sample (250 ml) was treated with a chelating resin (Chelex 100) at pH 6 for preconcentration of trace elements. After filtration with a glass filter, the resin on the filter was carefully rinsed with 8 ml of 1 M ammonium acetate solution. Then, trace elements adsorbed on the resin were eluted with 6 ml of 2 M HNO3. As a result, the preconcentration factor of 41.7 fold was obtained, with the total concentration of matrix elements (Na, K, Mg, and Ca) less than 200 mg dm−3. The recovery values were larger than 80% for 22 elements among 29 elements determined. The present method was applied to the determination of trace elements in the coastal seawater certified reference material CASS-3, issued from National Research Council of Canada (NRC), as well as to the coastal seawater sample collected f...

The progress of modern analytical atomic spectrometry is briefly reviewed with emphasis on ICP-AES and ICP-MS; these provide some excellent analytical features such as high sensitivity, wide linear dynamic range, and multielement detection capability. Thus, the multielement determination of the major-to-ultratrace elements from % to sub-ppt (1 ppt = 10−12 g ml−1) level is possible for the biological, geochemical, and environmental samples. The standard or certified reference materials of plant, human blood serum, and the other biological samples were analyzed to establish the reliable analytical methods for the multielement determination by ICP-AES and ICP-MS. The modern analytical methods were applied to: (i) the correlation analysis of the elements in human blood serum, and (ii) the determination of rare earth elements in human blood serum on a personal basis. The speciation of trace elements in natural water was also carried out by the SEC (size exclusion chromatography)/UV absorption detection/ICP-MS ...

An on-line separation-detection system, liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP-MS), has been developed and applied to the study on speciation of trace metals in pond water. First, the total concentrations of dissolved metal ions in pond water were determined by ICP-MS after chelating resin preconcentration. Then, pond water was preconcentrated by ultrafiltration using a filter with a molecular weight permeation limit of 10000, providing size exclusion chromatography. Large organic molecules which had combined with trace metals in the preconcentrated samples were separated with a gel filtration column and detected by UV absorption and ICP-MS, sequentially. In consequence, large organic molecules with the molecular weight of ≥300000 and 10000—50000 could be observed. A large number of trace metals (41 elements) were found in those organic molecules. Furthermore, the percentages of metal ions in the forms of large organic molecule–metal complexes were estimated f...

A discrete microsampling technique for multielement determination of trace elements by inductively coupled plasma mass spectrometry has been investigated for analyses of samples containing large amounts of matrix elements. In the technique, 100 μl of the sample solution was introduced into the plasma by using a six-way valve, and 10 elements were detected in peak hopping mode during a single mass range scan. As a result, a transient peak profile of the signal for each element was observed at each m/z position. The peak area measurement method was established for the quantitative analysis. The optimization of instrumental conditions and matrix effects in multielement determination were investigated in detail. The discrete microsampling technique was found to reduce some memory effects due to matrices in ICP-MS. The present system was applied to the analyses of standard sediment sample and 30 elements at the μg g−1 level were successfully determined without matrix separation.

An analytical method for multielement determination of trace and ultratrace elements in seawater has been investigated by using ICP-MS. Trace and ultratrace elements were preconcentrated by 10- or 20-times with addition of aluminum into seawater and then the elements were determined by ICP-MS. In this procedure, aluminum was added as the carrier for coprecipitation; it precipitated together with magnesium in seawater. Some trace elements were also measured by ICP-AES after coprecipitation. In addition, major and minor elements in seawater were determined by ICP-AES after dilution with acidified water. As the result, 37 elements in total could be determined in coastal seawater. The present results are compared with the concentrations of the elements in open seawater.

Rare earth elements in coastal seawater were preconcentrated by using chelating resin in a batch method and determined simultaneously by inductively coupled plasma mass spectrometry (ICP-MS). In this procedure, matrix components (Na, K, Mg, and Ca) were eliminated to reduce matrix effects in ICP-MS analysis and rare earth elements were concentrated by a concentration factor of 100. The pH dependence of the recovery, resin amounts, amount of ammonium acetate for washing, and elution of adsorbed metals with nitric acid were examined in details to optimize the experimental conditions in sample pretreatment. All rare earth elements in coastal seawater were determined at the ppt or sub-ppt level successfully by the present analytical method.

A hyphenated system of inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) combined with aid of optical fiber was developed for versatile simultaneous multielement measurement of the elements from the major to ultratrace levels. In the present system, the emission signals from the argon ICP equipped for ICP-MS were led through optical fiber to a sequential-type monochromator for ICP-AES measurement. In consequence, the dynamic range of 9 orders of magnitude from a few pg ml−1 up to ca. 1000 μg ml−1 was obtained, which allowed the simultaneous determination of a variety of elements in the wide concentration range by ICP-MS and/or ICP-AES. The present system was applied to simultaneous multielement analysis of rock and seawater samples.

The rapid determination of rare earth elements (REEs) has been investigated by an on-line system of high performance liquid chromatography/multichannel inductively coupled plasma atomic emission spectrometry. In the present system, all REEs could be detected simultaneously in a single chromatographic measurement without spectral interferences. Utilizing a cation exchange column and 2-hydroxy-2-methylpropanoic acid aqueous solution as the mobile phase, the detection limits of 0.4—30 ng ml−1 for all REEs were obtained. The system was applied to the determination of REEs in geological standard rock samples and rare earth impurities in high purity rare earth oxides. The REEs in standard rocks could be determined by the present HPLC/ICP-AES system without pretreatment after acid digestion, although the detection limits were not sufficient for the analysis of rare earth oxides.

A novel method for enantiometric separation using an ODS stationary phase coated with bile salt micelles in high-performance liquid chromatography has been developed, where bile salt surfactants such as sodium cholate and sodium deoxycholate were used for micelle formation. The present method was applied to the separation of the enantiomers of 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (BNDHP) and N-dansylphenylalanine by using acetonitrile–water solution as the mobile phase. The dependence of the capacity factors and separation factors on the acetonitrile concentration in the mobile phase was examined for BNDHP enantiomers. These factors decreased with increasing acetonitrile concentration, which resulted in the change of separation characteristics of BNDHP enantiomers. Although BNDHP and N-dansylphenylalanine enantiomers were separated, similar enantiomers such as 2,2′-dihydroxy-1,1′ -binaphthyl and other N-dansylamino acids were not separated in the present separation system.

Anions such as nitrite, nitrate, iodide, and thiocyanate ions contained in human saliva have been determined by ion chromatography using a microcolumn coated with micellar bile acid derivative, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, where only a phosphate buffer solution was used as the mobile phase. The detection limits obtained by the present system were 1.1 μM for nitrite and nitrate, 2.3 μM for thiocyanate, and 0.48 μM for iodide when the direct UV absorption detection of the anions was performed at 230 nm. The present system was applied to the determination of inorganic anions in human saliva, especially in relation with smoking habit, age and sex. Thiocyanate ion was detected at the significantly higher level in saliva for the smokers, compared to the non-smokers. Furthermore, the thiocyanate levels in saliva depended on the age and sex, while the concentrations of nitrite, nitrate, and iodide ions were rather independent of these parameters.

Concentration of trace metals forming complexes with large organic molecules in natural waters have been determined. Natural water samples (sea water and lake water) were filtered through a membrane filter (pore size: 0.45 μm) just after sampling, and concentrated by ultrafiltration. The concentrated natural water samples were fractionated by high performance gel filtration chromatography, and metal ion concentration in each fraction was determined by inductively coupled plasma atomic emission spectrometry and/or by graphite furnace atomic absorption spectrometry. Concentration of zinc forming large molecular complexes (LMC) in sea water was 0.07 ngmL−1, and that in lake water was 0.06 ngmL−1. Copper, iron, vanadium, and molybdenum forming LMC in natural waters were also determined. The present results suggest the existences of LMC-forming metal ions, some of which may be metalloenzymes dissolved in natural waters.

Flow injection analysis with spectrophotometric detection has been developed for the determination of phosphorus in biological samples. Potassium peroxodisulfate was used as an oxidizing reagent with aid of a platinum wire as the catalyst, and organophosphorous compounds were converted to orthophosphate which reacted with ammonium molybdate in the presence of ascorbic acid to form the molybdenum blue complex. The absorbance of the complex was detected at 880 nm.

Preconcentration of trace metals in seawater using a Chelex-100 resin column was investigated for simultaneous determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimum preconcentration conditions were examined in detail. With 100 ml of 1 M ammonium acetate buffer solution (1 M=1 mol dm−3), the matrix elements in seawater could be removed sufficiently without loss of analytes. The concentration factor of 200 times could be achieved by dissolving the dried HNO3 eluent of the column. The blanks of the method were negligibly small for most elements investigated. The detection limits were in the range of several ng/1 to 100 ng/1 for Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Ti, V, and Zn. The present technique was applied to the determination of trace metals in coastal and ocean seawater.

The distributions of neutral atoms in the nitrous oxide–acetylene flame have been measured by nebulizing aquo ions of the following sixteen elements into the flame; cadmium, nickel, zinc, copper, lead, cobalt, manganese, iron, chromium, molybdenum, calcium, tin, gallium, indium, titanium, and boron. The distributions have been figured on the response surfaces on which the changes in distribution are expressed as functions of the flame height and the acetylene flow rate. The response surfaces for the temperature and the OH radical were also investigated. The response surfaces for the atomic absorptions of the elements can be related to the thermodynamic properties of the oxides of the elements. The results have then been used for the discussion of the atomization processes of the elements in the flame. In addition, the sensitivities of absorption spectrometry in the nitrous oxide–acetylene flame have been compared to those in the air–acetylene flame.

A method for the determination of trace zinc has been investigated using hydro-lyase activity of carbonic anhydrase. It was proved theoretically and experimentally that the activation rate of the apo-carbonic anhydrase with zinc is proportional to the amount of zinc present in the solution. Hydro-lyase activity was measured electrochemically using sodium hydrogencarbonate as a substrate. The limit of detection was 0.89 ng/ml or 40 pg of zinc, lower than that obtained by the esterase activity method. Application of the present method to the determination of zinc in real samples has been examined in order to evaluate its analytical feasibility.

Metalloenzyme (alkaline phosphatase) dissolved in lake water has been identified by means of high performance liquid chromatography (HPLC). Water samples were collected from Lake Kasumigaura in Ibaraki, and filtered with a 0.2–0.45 μm membrane filter immediately after sampling. Filtered water was concentrated to 100–2000 fold by ultrafiltration membrane which could concentrate the components of molecular weight larger than 10000. The enzymatic activity of alkaline phosphatase was measured using p-nitrophenyl dihydrogen-phosphate as a substrate. Chelating agents added to the concentrated lake water inhibited the appearance of enzymatic activity, while the enzymatic activity was recovered with addition of zinc ion. The HPLC chromatograms of the concentrated lake water were examined, where an aqueous porous gel column was used for separation. The effluent at molecular weight of ca. 90000 showed specific activity of alkaline phosphatase. Zinc was also found in the same fraction. These facts suggest that alkal...

The atomic absorption spectrometry of indium was investigated in air-acetylene and nitrous oxide-acetylene flames. The atomic absorptions of indium were significantly interfered by HCl, HClO4, and HBr in both the flames. The chemical interferences can be explained by the formation of diatomic molecules, such as InCl and InBr, the molecular absorption spectra of which were really observed in flames.

The coprecipitation of trace metals with gallium has been investigated in detail especially with respects to the role of magnesium ion in saline or seawater. Gallium does not precipitate even at pH 9 when magnesium ion does not exist. The concentration of gallium in the precipitate increased with increasing that of magnesium in solution. The recoveries of trace metals also showed strong dependence on the concentrations of both gallium and magnesium in the aqueous solution.

A method for the determination of trace zinc has been investigated by using enzymatic activity of carbonic anhydrase. The recovery of enzymatic activity of apo-carbonic anhydrase was proportional to the amount of zinc in solution theoretically and experimentally, when it was monitored spectroscopically using the substrate, p-nitrophenyl acetate. The amount of zinc in the sample solutions was therefore determined from the curve, zinc concentration vs. the enzymatic activity. The limit of detection is 10 ng/ml or 2 ng. The method has been applied to the analysis of zinc in fruit juices and water samples.

Rare earth elements (REEs) in twelve standard rock samples have been determined by inductively coupled plasma atomic emission spectrometry after separation of diverse metal ions with cation exchange resin. These rock samples are old six standard rocks (W-1, BCR-1, AGV-1, GSP-1, JB-1, JG-1) and new six standard rocks (JB-2, JB-3, JA-1, JR-1, JR-2, JGb-1) issued from the Geological Survey of Japan. These samples are various types of igneous rocks, which show various shapes of the REE distribution patterns. Geochemical characteristics of these standard rock samples will be discussed from the relationships between rock types and the shapes of the REE pattern.

The identification of rock-forming and clay minerals contained in the reference material of “Pond Sediment” (Reference Material NIES No. 2 from the National Institute for Environmental Studies, Japan) has been made with X-ray diffraction method. It was found that the sediment contained α-quartz and feldspars as the principal components along with small quantity of pyroxenes, amphiboles, and some clay minerals. The sediment sample was treated chemically for extraction, and also separated with density and with grain sizes. Elemental compositions of such extracted or separated fractions of the sediment were determined by inductively coupled argon plasma emission and atomic absorption spectrometry. The identified minerals and the elemental distributions in the separated fractions helped to characterize the pond sediment.

A multielement detection system which uses a programmable monochromator and a SIT image detector has been constructed, and evaluated by measuring the flame emission of 22 elements in the nitrous oxide–acetylene flame. The detection limits for the elements under optimized experimental conditions are reported, and are compared with those obtained by a standard photomultiplier tube.

A preliminary study on analytical performances of graphite sample cups is described for an instrumental assembly to carry out microliter volumes of liquid sample analysis. The graphite cup with a graphite rod and an insulating handle is inserted axially via the injector tube of a quartz torch into a low power operated inductively coupled argon plasma. Univariate search method has been employed for optimization of cup size, rod height and plasma operating parameters for manganese ionic line at 257.6 nm to obtain the most favorable net signal-to-background ratio. Detection limits, reproducibilities and dynamic ranges are also reported for manganese, zinc, lead, chromium, and nickel in solution.

A simple and convenient analytical method for simultaneous multielement determination of soil and rock samples has been investigated by inductively coupled plasma emission spectrometry. Spectral interferences due to major elements were examined in detail, and the correction coefficients for minor and trace elements were estimated for correction of matrix effects. The determinations of minor and trace elements as well as major elements could be performed without matrix matching of the standard solutions. The present method investigated has been applied to the analysis of various soil and rock samples, and the analytical results have been compared with those obtained by atomic absorption spectrometry.

Alkaline phosphatase activity (both dissolved and total) in Lake Kasumigaura was determined periodically together with concentrations of phosphorus compounds therein. Distinct negative correlation was found between the dissolved alkaline phosphatase activity and the orthophosphate concentration during the phosphorus-limited season. The decrease of the concentration of dissolved alkaline phosphatase was observed at the level of 1 ng ml−1 of orthophosphate. The present results suggest that both alkaline phosphatase in vivo and dissolved alkaline phosphatase in the lake water play important roles in phosphorus cycles in natural water.