Phosphorus circulation

Phosphate is often referred to as phosphorus, a practice that is inaccurate and misleading because only phosphate, not elemental phosphorus, circulates in blood and is measured. This practice originated because results are reported as milligrams per deciliter of phosphorus, rather than phosphate. When results are reported in molar units (as in SI), the numerical results and reference intervals are the same for phosphorus and phosphate, but confusion occurs when results are reported in mg/dL. 

The Phosphate Cycle.—Phosphorus circulates in the kingdoms of life in the oxidised form of phosphate. Plants elaborate soil phosphate into phospholipides and other phospho-compounds, which are transformed by the animal into phosphoproteins and tissue phosphates, the residue being returned to the soil or the sea as metallic phosphate. Soil phosphate is one of the important limiting factors in plant growth, and its provision is one of the tasks of applied agriculture. 

The most commonly used physical method for long-term eutrophication control in lakes is that of artificial destratification. This method is well tried and understood and uses either jetted water or compressed air bubbles to break down the lake stratification in the summer months. Algal growth is also affected by an increase in circulation. This is due to the artificial shading effect which results from the algae spending less time near the surface and consequently less time in the light. This technique also reduces the redox-dependent phosphorus release from sediments because the sediment surface remains aerobic. 

Phosphorus also occurs in all living things and the phosphate cycle, including the massive use of phosphatic fertilizers, is of great current interest.O 20) -pj.jg movement of phosphorus through the environment differs from that of the other non-metals essential to life (H, C, N, O and S) because it has no volatile compounds that can circulate via the atmosphere. Instead, it circulates via two rapid biological... 

Vitamin D3 is a precursor of the hormone 1,25-dihy-droxyvitamin D3. Vitamin D3 is essential for normal calcium and phosphorus metabolism. It is formed from 7-dehydrocholesterol by ultraviolet photolysis in the skin. Insufficient exposure to sunlight and absence of vitamin D3 in the diet leads to rickets, a condition characterized by weak, malformed bones. Vitamin D3 is inactive, but it is converted into an active compound by two hydroxylation reactions that occur in different organs. The first hydroxylation occurs in the liver, which produces 25-hydroxyvita-min D3, abbreviated 25(OH)D3 the second hydroxylation occurs in the kidney and gives rise to the active product 1,25-dihydroxy vitamin D3 24,25 (OH)2D3 (fig. 24.13). The hydroxylation at position 1 that occurs in the kidney is stimulated by parathyroid hormone (PTH), which is secreted from the parathyroid gland in response to low circulating levels of calcium. In the presence of adequate calcium, 25(OH)D3 is converted into an inactive metabolite, 24,25 (OH)2D3. The active derivative of vitamin D3 is considered a hormone because it is transported from the kidneys to target cells, where it binds to nuclear receptors that are analogous to those of typical steroid hormones. l,25(OH)2D3 stimulates calcium transport by intestinal cells and increases calcium uptake by osteoblasts (precursors of bone cells). 

Humans occupationally exposed to phosphorus probably ingested some airborne white phosphorus. In a study of 71 humans occupationally exposed to fumes/vapors and paste containing white phosphorus, oral exposure to phosphorus passed from hand to mouth was likely, because the workers constantly handled a paste containing 4-6% white phosphorus, and washroom facilities at the plants were inadequate (Ward 1928). White phosphorus-related deaths occurred in 0 of 44 and 2 of 27 of the workers exposed for intermediate and chronic durations, respectively. In the two cases of death, the workers died from complications related to phossy jaw, a degenerative condition affecting the soft tissue, bones, and teeth of the oral cavity. In this condition, the toxic effects of white phosphorus probably result from the local irritant action of white phosphorus on tissues in the mouth. Thus, white phosphorus paste passed from hand to mouth and the local action of airborne white phosphorus on the oral cavity may have contributed to the development of phossy jaw, and subsequent death, of these two workers. It is not known whether white phosphorus ingested and absorbed into the systemic circulation contributed to the development of phossy jaw in the two workers that died (Ward 1928). Details of this study are provided in Section 2.2.2.2. 

It is likely that the effect of white phosphorus in the oral cavity is local, resulting from contact of "inhaled" white phosphorus particles with tissue in the mouth. White phosphorus may affect the oral mucosa. Dull, red spots in the oral mucosa, an early sign of phossy jaw, have been reported to precede its development in occupationally exposed workers (Kennon and Hallam 1944). The oral mucosa of workers exposed to white phosphorus has been described as having a dull, red, unhealthy appearance (Hughes et al. 1962). Exposed bones may be especially susceptible to the irritating affects of white phosphorus. It is not known whether white phosphorus ingested and absorbed into the systemic circulation contributed to the development of phossy jaw. 

Su, L., H. Zhang, Q. Wang, and H. Xie. 2007. On-line microwave digestion for the determination of total phosphorus in circulating water by flow injection spectrophotometry. Gongye Shuichuli 27 80-82. 

The oxidation of butane (or butylene or mixtures thereof) to maleic anhydride is a successful example of the replacement of a feedstock (in this case benzene) by a more economical one (Table 1, entry 5). Process conditions are similar to the conventional process starting from aromatics or butylene. Catalysts are based on vanadium and phosphorus oxides [11]. The reaction can be performed in multitubular fixed bed or in fluidized bed reactors. To achieve high selectivity the conversion is limited to <20 % in the fixed bed reactor and the concentration of C4 is limited to values below the explosion limit of approx. 2 mol% in the feed of fixed bed reactors. The fluidized-bed reactor can be operated above the explosion limits but the selectivity is lower than for a fixed bed process. The synthesis of maleic anhydride is also an example of the intensive process development that has occurred in recent decades. In the 1990s DuPont developed and introduced a so called cataloreactant concept on a technical scale. In this process hydrocarbons are oxidized by a catalyst in a high oxidation state and the catalyst is reduced in this first reaction step. In a second reaction step the catalyst is reoxidized separately. DuPont s circulating reactor-regenerator principle thus limits total oxidation of feed and products by the absence of gas phase oxygen in the reaction step of hydrocarbon oxidation [12]. 

Vitamin D regulates calcium and phosphorus absorption and deposition and serum alkaline phosphatase levels. The recommended daily allowance is 5 /xg, increasing to 10 to 15 /xg in older age.109 Vitamin D3 is synthesized under UVB irradiation in the skin where it is stored and released into the circulation in a complex with the vitamin D binding protein. In liver it is hydroxylated to 25(OH)-cholecalciferol, the hormonal precursor, followed by another hydroxylation step in the... 

Vitamin D that is taken up by the fiver is converted to 25-hydroxyvitamin D by a microsomal hydroxylase (Fig. 30-3). 25-Hydroxyvitamin D is the main circulating form of vitamin D in the serum and the best indicator of vitamin D status. Normal serum levels are 14-60 ng/mL (35-150 nmol/L). When serum calcium concentrations decline, 25-hydroxyvitamin D is converted to 1,25-dihydroxyvitmin D by la-hydroxylase, a mixed-function oxidase that is located in the inner mitochondrial membrane in kidney tissue and whose expression is regulated by parathyroid hormone (PTH). The main function of 1,25-dihydroxyvitamin D is to increase the intestinal absorption of dietary calcium and phosphorus. When serum concentrations of calcium and phosphorus are normal or when large doses of vitamin D are administered, 25-hydroxyvitamin D is metabolized to 24,25-dihydroxyvitamin D in the renal... 

From the earliest ages the natural circulation of phosphorus has been altered and controlled by farmers. The systematic return of all kinds of excreta to the soil is still the basis of the intensive cultivation practised in densely populated areas of India and China, where the soil bacteria are so active at the favourable temperature prevailing that the nitrogen and phosphorus become available almost at once for another crop. The return of bones to the soil is a less obvious form of economy, partly because when in the massive form these disintegrate very slowly. 

Occurrence and Circulation op Phosphorus —-Mineral Phosphates—Assimilation by Plants—Sources of Phosphates—The Composition of Phosphorites —-The Distribution of Phosphatic Rooks—Ooeanio Deposits and Guanos—-The World s Production of Phosphate Rook. 

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