The Phosphorus Cycle

The Phosphorus Cycle

Phosphorus Properties

Atomic Number: 15Melting Point: 111.5 F (44.15 C)Boiling Point: 536.9 F (280.5 C)Nonmetal, part of nitrogen groupFound in nature in several allotropic forms; White, red & black.White created industriallyEssential element for lifeLimiting NutrientIn nature, never encountered in pure form, mostly as phosphateExists primarily as POFirst discovered in 1669, by Hennig Brand, when first isolated in a pure form from urine.

Credit: Greg Robson/Creative Commons, Andrei Marincas | ShutterstockPhosphorus Properties ContinuedDoes not have a stable gaseous phase in atmosphereExists as AerosolsPhosphorus is locked up is rock3 Sources: Bedrock, Soil & Biomass4 Components: Riverine sediment transport, Physical erosion, Exposure of P bearing rocks & tectonic uplift. Photosynthetic organisms utilize dissolved phosphorous, carbon and other esthetical nutrients to build their tissues using energy from the sun.Biological productivity is contingent upon the availability of phosphorous food web both from terrestrial and aquatic systems.

The most common mineral on that contains phosphorus is Apatite Ca5(PO4)3(OH,F,Cl). Phosphate minerals with high concentrations of apatite are mined.Anthropogenic release of Phosphorus

Uses of PhosphorusFertilizers (Red)Pesticides (Red)Steel ProductionMilitary ApplicationsIncendiary bombs, smoke screening (White)Pyrotechnics (White)Household ProductsToothpaste, DetergentsProduction of LEDsSoft DrinksChinaBaking Soda

Photo courtesy of: http://news.naij.com/33525.htmlPhoto courtesy of: http://economicdevelopment.missouri.edu/features/2011/am-pyrotechnics/index.php

Global Phosphorous CyclePhosphorous Cycle has 4 major components:Tectonic uplift Exposure of P bearing rocksPhysical Erosion River

Terrestrial Phosphorus CycleWeathering of continental bedrock is the prime source of phosphorus soils which support vegetation growth.P-mineral in crustal rocks.Weathering reactions driven by exposure of minerals to natural acids from microbial activity.

Marine: Transport of Phosphorus~20-40 % of P is suspended particulate matter is organicInorganic forms are divided ferricoxyhydroxide (HFeO2) and Apatite .

Continents to Ocean

Groundwater seepage to coastal ocean poorly documented.

Dissolved phosphorous in rivers occurs in both organic and inorganic forms.

Riverine P depends on drainage basinsPhosphorous PHAt Low PH values and least soluble P phases are those that contain iron and aluminumVivianite (Fe2+Fe2+2(PO4)28H2O) Strengite FePO42H2OVariscite AlPO42H20Phosphorous PHAt high PH values least soluble P are in the mineral apatite.Phosphorus solubility is greatest at intermediate levels of PH found in natural waters

Phosphorus Cycling In AtmosphereNo stable gas phaseTotal Phosphorus exists as AerosolsSources:Mineral Aerosols (dust) 82%Biogenic Aerosols - 12%Spores or pieces of plants emitted directly to the atmosphere.Combustion SourcesCoal, Oil boilers, gasoline & diesel engines, incineratorsSea Salt AerosolsPOVolcanic Aerosols Very Small Amount from SwampsPHPhosphorus Cycling in Lithosphere 11th most abundant element in Earths crustMost common mineral is ApatiteMining of Phosphate DepositsMined for use in agriculture and industry2005 17.5 million tons minedMines found in North American (especially Florida), Africa (Egypt, Morocco, Tunisia), Middle East (Isreal, Saudi Arabia, Jordan, Iraq), AustraliaByproducts of mining phosphate Cadmium, lead, nickel, copper, chromium & uraniumIf not managed correctly, these heavy elements can leach into groundwater & estuaries.Bioaccumulation of toxic substances

Courtesy of http://en.wikipedia.org/wiki/File:Train_loaded_with_phosphate_rock,_Metlaoui_Tunisia-4298B.jpgPhosphorus deposits on ocean floorVia decomposition, deposition, mineralizationSedimentationPhosphorus bearing rocks can be recycled into mantle at subduction zones or uplifted Uplift causes rock to become exposed and erode due to physical and chemical weatheringAs the rock erodes phosphorus is released into the soil

Phosphorus Soil ReservoirSoil reservoir (up to 50 cm depth) 46x10 g P, only ~13.8x10 g is labileSmall fraction of total P available to biotaRelative amounts vary amongst different soilsRecycling of organic P extremely importantMajor regulator of bio-productivity in weathered soils.

AvailabilityWeathering of phosphate mineralsWeathering of sedimentary rockSoil microbes, mycorrhizae, & plants roots increase P availabilityMineralization: organic P released by microbes via decompositionFertilizersVery small percentage is deposited from the atmosphere

LimitationsSorption most important process limiting P availabilitySorptive binding of P to Fe & Al oxides make P unavailableLeached from soilImmobilization: available P taken up by microbesLess weathered soils have a more even limitation based on both P and NitrogenPhosphorus is lost from terrestrial systems due to run-offEnhanced by anthropogenic activityAlso lost through crop harvesting17Terrestrial P Cycle

18Phosphorus Cycling in HydrospherePrimarily transported to ocean through rivers as a result of weathering and small percentage from leaching.On average 0.1% PO (Diphosphorous tetroxide)River TransportDissolved and particulate phasesPrimarily particulate phase in river systemPhosphorus enters the ocean in dissolved phase. Exists as organic and inorganic20-40% Phosphorus is organicInorganic forms are ferric oxyhydroxides & ApatiteFlux estimates for riverine discharges range between 27x 10 mol/year for inorganic and 2.9x10 mol/year for organic phosphorus.Difficult to calculate exact river discharge flux due to anthropogenic input (ex. Deforestation, leaching from fertilizers)LakesPhosphorus from soil erosion and decomposition of organic matter.

4 processes serve as Phosphorous removal mechanismsOrganic matter burial decompositionP-sorption & precipitation with clays and iron hydroxide particles. Phosphorus can be absorbed onto shells made of CaCO via iron oxyhydroxide coating.Burial of Phosphate particlesHydrothermal processesVent fluids contain large amounts of reduced Fe. Quickly oxidizes to form ferric oxyhydroxidesEfficient in scavenging dissolved phosphorus

Phosphorus Cycling in Hydrosphere ContinuedNon-point runoff causes an influx of Phosphorous into lakes and estuaries that can cause eutrophication. Algae blooms caused by excess of nutrientsMinor sink Phosphorus uptake through seawater & oceanic crust interactions associated with hydrothermal activity on ocean floor. Marine SedimentsA sink for phosphorus in oceanLess than 1% of phosphorus that reaches the ocean floor gets buriedOrganic Phosphorus subject to break down via microbial respirationMarine respiration Redfield ration 106C:1P

Phosphorus Cycling in BiospherePhosphorus us an essential element to all lifeStructural and functional component of all organismsProvides the phosphate-ester backbone of DNA & RNACrucial in transmission of chemical energy through ATP moleculeStructural constitute in phosphoprotiens and phospolipids in cell membranes, teeth and bones.Acts as a pH buffer in blood.Uptake of Phosphorous by plants through soil. Phosphorous deficiency can cause color changes in plantsPhotosynthesis restrictedCan cause plants to die offDecomposition returns phosphorous into soilUptake of Phosphorous by organismsMarine organisms can secrete Phosphorous through flocculationAnimals eat algae and other organismsDie, decompose, phosphorous returned to ocean system.

Deficiency Affect plant growth and rate of photosynthesisResearch on bean plant culture removal of phosphate from the nutrient rich solution affected growth of bean plants.

Impacts On Other CyclesCarbon CycleRedfield ratio needs for respiration 106C:16N:1PNitrogen CyclePhosphorus is essential for Rhizobium bacteria to convert atmospheric N (N) into Ammonium (NH) Iron CycleUpon decomposition of organic matter, the iron redox cycle provides an effective means of trapping phosphate in sedimentsSulfur CycleIn fresh water systems, low SO (sulfate), Phosphorus is strongly absorbed by elements in sediments.Lakes High SO from acid rain and pyrite mining will have an anion exchange reaction which drives Phosphorous into solution.ChemistryPhosphoric Acid Disassociationka= 2.4 x 10 = [PO][H+] = (8.86x10)(10) [H PO] [H PO]= (8.86x10)(10) = [H PO] (Hydrogen Phosphate) = 1.057 x 10 (4.2x 10 ) Low Concentration [PO] 7PPM = Mg/LiterOcean Water pH= 8.3Conversion=7x 10 g x 1 Mole PO = 8.86x10 Mol L (Low)Liter 79 g 70 PPM -> 70 x 10 x 1 Mole PO = (8.86x10)(10) = 1.057 x 10 (High) Liter 79 g (4.2x 10 ) River-Lakes Rainwater pH=5.65[H PO] = (8.86x10)(10) = Low Concentration 4.2 x 10 (4.2x 10 ) *Comparison of the high concentrations of HPO is in the order of 2 magnitudes.

One can work backwards to obtain Phosphoric AcidHPO HPO + [H+] ka = 7.5 x 10 MolarHPO HPO + [H+] ka = 6.2 x 10 MolarHPO PO + [H+] ka = 4.2 x 10 Molar

ka = [HPO] [H+] [HPO ]ka = [HPO] [H+] [HPO]ka = [PO] [H+] [HPO]Choosing High [PO] 10 PPM pH=5.65 Terrestrial Water Sources[HPO][H+] = (8.86x10)(10) = 3.20 x 10 Molar [HPO] ka=6.2x10 6.2x10

[HPO] [H+] = (3.20 x 10)(10) = 9.55x10 Molar [HPO] ka=7.5x10 7.5x10

Choosing pH=8.3 Ocean water with High [PO] 70PPM(1.057x10)(10) = 8.54 x 10 Molar [HPO] 6.2x10(8.54x 10)(10) = 5.71 x 10 Molar [HPO] 7.4x10

*Observed changes in concentrations have been simplified excluding affects of salinity and other competing ions.Gibbs Free Energy All data derived from standard state thermodynamic data tablesCa(PO)OH + 4HCO 5Ca+(aq) + 3HPO(aq) + 4HCO(aq)+HO (l) [Hydroxyapatite]-6338.3 kJ mol + 4(-623.14) 5(-552.8) + 3(0) + 4(-586.8) + (-237.14) Gf = Gf Products - Gf Reactants = (-2764) + (-2347.20) + (-237.14) (-6338.3) + (-2492.56) = (-5348.34) + 8830.86 = 3482.52 kJ/mol Empirical Evidence Endothermic Process

Al+(aq) + HPO(aq) + 2H0 (l) AlPO + 2HO (l) + H+0 + 0 + 2(-237.14) (-2097.8) + 2(-237.14) + 0 Gf= Gf Products - Gf Reactants = (-2097.80) +(-474.28) (-474.28) = (-2572.08) + 474.28 = - 2097.80 kJ/mol Exothermic

White Phosphorus Reaction

White phosphorus ignites spontaneously on a filter paper. P (white) + 5O --> POCurrent IssuesSoil levels in Europe and North America have surpassed critical phosphorus levels and demand for phosphorus has stabilized in these regions

Estimated 2-2.5 billion new mouths to feed by 2050 mainly in developing world

Global food production will need to increase about 70% to meet this global demand

Increase in popularity of meat and dairy based diets have led to increase in phosphorus demand

As well as increasing concern of oil scarcity and climate change has led to a sharp increase in biofuel production

Biofuels is found to consume about 2% of the global inorganic P fertilizer production.

Approximately 50-100 years remain of current known reserves

Remaining phosphate reserves are under the control of a handful of countries, China, the U.S and Morocco.

Current IssuesClose to 100% of phosphorus eaten is excreted

Global population excretes around 3 million tons of phosphorus in urine and in feces and are becoming phosphorus hot spots

Recycle phosphorus from human wasteEach person excrete 1.2 grams of Phosphorus a day. Trapping this can produce ~3 million tons per year.One method is to extract struvite (magnesium ammonium phosphate) from waste at sewage treatment plants and processing into pellets.Urine separating toilets and latrines already deployed in Europe. Installed in Durban, South Africa. Peepoo, single use, self sanitizing, biodegradable bag that captures human waste (yes, your poop) and can be used and sold as fertilizer 2-4 weeks later. Over fertilization of agricultural soils is common in the northern hemisphere and contributes to excess discharge into water bodies and causes eutrophication

25% of the 1 billion tons of phosphorus mined since 1950 has ended up in bodies of water and buried in landfills.

Toxic byproduct of each ton of phosphate processed from phosphate rock generates 5 tons of phospho-gypsum

Cannot be used in most countries due to high radiation levels, which grow by over 110 million tons each stockpile.

Risk of leakage to groundwater.What Can We Do?No quick fix to the problemPhosphorus can be recovered from food production and consumption system and reused as fertilizerDevelopment on research of struvite In some urban areas in Pakistan and Asia more than 25% of vegetables are being fertilized with wastewater from cities.About 200 million farmers worldwide use wastewater to irrigate crops67% of global yields of farmed fish are fertilized by wastewaterIf urine is not mixed with fecal matter, it can be used safely through storageUrine is essentially sterile and could provide more than half the phosphorus required to fertilize cereal crops. Ex. In Sweden, two municipalities have mandated that all new toilets be urine diverting Local farmers collect urine about once a year as liquid fertilizerAnother approach is the addition of microbial inoculants to increase soil phosphorus availability.EutrophicationGlobally estimated that annual accumulation of phosphorus in Earth's freshwater and terrestrial ecosystems has almost quadrupled.

Under natural conditions eutrophication can be centuries-long aging process but when human caused can happen in a few years.

Eutrophication studied since the turn of the twelfth century but not recognized as widespread international problem until the 1950-60s.

Efforts to reduce phosphorus inputs into aquatic ecosystems by diverting sewage and cutting off point sources

By 1990's phosphates were also removed from detergents

Yet eutrophication persisted..

Eutrophication continued..This was due to non point pollution sources

Currently non point runoff is main source of phosphorus to most aquatic systems

Ex. Hypoxic zone in the Gulf of Mexico caused by grain growing states of the midwest, carried to the gulf by the Mississippi River.

The leakage of phosphorus from agricultural land has caused harmful algal blooms and this is a large concern for people

Became the largest motivation to take measures to efficiently use phosphorus.Harmful Algal BloomsAlgal populations that grow extensively and may produce harmful toxins

Non toxic blooms are also hazardous because they suffocate fish, blocking light and depleting oxygen from water

Consuming these algal contaminated shellfish may result in many illnesses.

They have cultural and economic implications, specifically in coastal communities dependent on harvesting seafood and tourism

In the U.S alone there have been an economic impact estimate of $82 million each year.

China July 2011

China July 2013

In AdditionDespite of the continually depleting reserves of phosphorus it is still used for reasons other than food production or alternative energy sourcesPyrotechnics although recently decreased, the amounts used still is effective in creating environmental problems

Chemical weapons