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The phosphorus mass balance: identifying ‘hotspots’ in the food system as a roadmap to phosphorus security
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The phosphorus mass balance: identifying ‘hotspots’ in the food system as a roadmap to phosphorus security Dana Cordell1, Tina-Simone Schmid Neset2 and Timothy Prior1 Phosphorus is a critical element on which all life depends. Global crop production depends on fertilisers derived from phosphate rock to maintain high crop yields. Population increase, changing dietary preferences towards more meat and dairy products, and the continuing intensification of global agriculture supporting this expansion will place increasing pressure on an uncertain, but finite supply of high-quality phosphate rock. Growing concern about phosphorus scarcity and security, coupled with the environmental impact of phosphorus pollution, has encouraged an increase in research exploring how phosphorus is used and lost in the food system — from mine to field to fork. An assessment of recent phosphorus flows analyses at different geographical scales identifies the key phosphorus ‘hotspots’, for example within the mining, agriculture or food processing sectors, where efficiency and reuse can be substantially improved through biotechnological approaches coupled with policy changes. Addresses 1 Institute for Sustainable Futures, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia 2 Centre for Climate Science and Policy, Dept. of Water and Environmental Studies, Linko¨ping University, 601 74 Norrko¨ping, Sweden Corresponding author: Cordell, Dana ([email protected])
Current Opinion in Biotechnology 2012, 23:839–845 This review comes from a themed issue on Phosphorus biotechnology Edited by Andrew N Shilton and Lars M Blank For a complete overview see the Issue and the Editorial Available online 12th April 2012 0958-1669/$ – see front matter, # 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.copbio.2012.03.010
Introduction Phosphorus scarcity has gained increased attention on the research and policy agenda over recent years, partially due to the 800% phosphate rock price spike in 2008 [1,2,3,4]. However, actual estimates of phosphate depletion or peak phosphorus vary widely, from the critical point occurring in 30–40 years to 300–400 years [2,5–8]. These estimations diverge due to various reasons, ranging from the uncertainty in volume and quality of the global reserves, to the estimates of future demand (with the more optimistic studies assuming no growth in phosphorus demand). In addition to more comprehensive global analyses, there remains a need to assess regional and national vulnerability www.sciencedirect.com
to phosphorus scarcity in order to guide appropriate responses to ensure phosphorus security. Phosphorus security means ensuring access to sufficient phosphorus to produce enough food to feed the population, while at the same time restoring/maintaining ecological integrity and farmer livelihoods [10]. Phosphorus is required for food production and its consumption maintains vital human functions, such as transporting energy to the brain and building cell walls [9]. Humans require only approximately 1.2 g/person/day — amounting to three million tonnes of phosphorus per year for the global population. However, around fivefold this amount is mined annually to produce fertilisers for food production because of the substantial losses and inefficiencies in the global food system from mine to field to fork [2]. Achieving phosphorus security will require an integrated approach that combines supply-side technologies and strategies (such as recovering phosphorus from mine waste, food processing and sanitation waste streams for reuse in agriculture) with demand-side measures (such as increasing efficient use of phosphorus in fertiliser and food production or changing diets) [2,10]. However, there is currently insufficient baseline data on phosphorus in the food system (such as the distribution of organic sources of phosphorus from manure, excreta, food waste). Establishing a phosphorus mass balance for a given city, region or country using Substance Flow Analysis (SFA) allows scientists to estimate how phosphorus flows through the anthroposphere (‘human’ system), thereby assessing the potential contribution of such technologies and strategies. The magnitude of these flows varies widely between countries, underlining the importance of national or multi-scale analyses. As such, SFA is considered a fundamental tool for improved phosphorus management [11]. This article reviews existing phosphorus SFAs and assesses their scope, key findings and major phosphorus losses. From this analysis, generalisations, knowledge gaps and implications are noted, including an identification of the potential for sustainable biotechnology innovations that can respond to the phosphorus security challenge.
Phosphorus flow analysis Substance flow analysis (SFA): a tool for managing phosphorus
Since the early 1990s, Substance Flow Analysisa (SFA) has been used to examine resources such as water and a
Also referred to as Material Flow Analysis (MFA) [12]. Current Opinion in Biotechnology 2012, 23:839–845
840 Phosphorus biotechnology
Figure 1
EXPORT SYSTEM BOUNDARY NATURAL ENVIRONMENT (air, soil, water) ANTHROPOSPHERE Industry/ trade/ commerce
Waste management
Household
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IMPORT
LEGEND: material flux influenced by the market emissions from Anthropogenic sources geogenic fluxes
Current Opinion in Biotechnology
Conceptual substance flow analysis diagram showing the interactions between the ‘anthroposphere’ (human activity system) and the natural environment. Redrawn from Baccini and Brunner [17].
energy [13], metals and toxic substances [14,15] at a wide range of geographical scales (from global to local). The method was established in the field of Industrial Ecology to aid environmental management by assessing the ‘metabolism’ of human or technical systems, often referred to as the technosphere or anthroposphere [16,17]. The method is based on the principle of mass balance, which enables a systematic assessment and tracking of the flow of goods, materials or substances between various processes in the relevant sectors, as well as imports to and exports from the system that are typically measured in units of mass per year (Figure 1). SFAs can aid the identification of key flows or ‘hotspots’ of the substance under investigation, thereby facilitating more effective and prioritised management of the substance within that system. However, SFAs only provide a Current Opinion in Biotechnology 2012, 23:839–845
quantitative (rather than qualitative) picture, and data availability and reliability are often poor. Nutrients, and in particular phosphorus, have been the subject of many substance flow studies. The early focus of this work was primarily pollution and leakage, but has more recently shifted to assessments of scarcity and food security, as the latter issues have received increased attention [18,19,20]. A recent (July 2011) workshop focused on national-level phosphorus SFA studies [19] stressed that both pollution and scarcity aspects are important to include. The workshop demonstrated the need for an integrated assessment of phosphorus flows between sectors (such as fertiliser, food and sanitation sectors) at the national/regional scale in order to decrease losses and increase efficiency, recovery and reuse of phosphorus within the food system. www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 841
Assessment of recent phosphorus flow analyses
The matrix in Figure 2 presents the results of a review of 18 recent phosphorus SFA studies in terms of geographical and temporal coverage, scope (pollution, scarcity) and sectors of the food production-consumption system. Criteria used to select these papers included: post-2005 phosphorus SFAs articles; peer-reviewed; an equal spread of geographical scale (global, national, regional, city) and continents; articles that addressed pollution and scarcity; and multi-sectoral studies (i.e. covering the entire food
production/consumption system from mining through to food consumption and waste). The geographical scale of the reviewed articles ranged from city-wide phosphorus SFA studies to catchments, nations, regions and the global scale. Regardless of scale, the primary objective of most studies was environmental management of phosphorus, particularly through a focus on agricultural losses and waste management in the wastewater sector [21,22,23]. A majority of the most
Figure 2
Agriculture
Food production &
Household
Waste
Pollution and leakage
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Cordell et al. (2009)
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Liu et al. (2008)
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Villalba et al. (2008)
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Bouwman et al. (2011)
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P SFA study
Schröder et al. (2010)
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19702000
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EU
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2006/7
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Shucheng county, China
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2008
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Japan
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2002
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2007
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Turkey, Austria
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~2007 -
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19902006
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Yuan et al. (2011) Matsubae-Yokoyama et al. (2009)
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Cordell & White (2010)
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Seyhan (2009)
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Suh & Yee (2011)
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Senthilkumar et al. (2011)
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Smit et al. (2010) Gumbo (2005)
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Helsinki Commission (2005)
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Montangero et al. (2007)
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Neset et al. (2008)
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Sectors Mining & fertilizer production
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France The Netherlands
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Zimbabwe
Lake Chivero
Harare
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Hanoi
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19802000 2000
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20012006
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Linköping
18702000
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Tangsubkul et al. (2005)
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Sydney
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2000
Qiao et al. (2011)
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Beijing, Tianjin
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2008
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Current Opinion in Biotechnology
Assessment of 18 recent phosphorus SFAs spanning different geographical scales, regions, scopes and sectors. www.sciencedirect.com
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recent studies included a discussion on phosphorus scarcity and explicitly highlighted opportunities for increased efficiency, recovery and reuse to meet the future challenges of phosphorus supply for food production [18,24]. Most studies noted low data reliability and the need for improved and standardised reporting.
livestock in Poland and wastewater discharges from diffuse and point sources) and emphasised the need for joint efforts between the Baltic Sea countries and improvement of agricultural practises (and development of associated policy measures) to reduce diffuse emissions from agriculture and other diffuse sources.
With respect to sectors, almost all studies analysed agriculture, household and wastewater sectors, and losses to the environment (water bodies). However, the processes between agriculture and household sectors were often collapsed into one box or flow (often termed ‘industry’) despite the food production, processing, trade and retail system being a long and complex chain resulting in substantial phosphorus losses in organic and food waste [10]. Similarly, phosphorus flows associated with mining, processing and fertiliser production were often not quantified despite recent estimates suggesting phosphorus losses in this subsystem may be substantial [10,25,26].
City level studies showed more variation in key phosphorus flows, largely since they represent the specific characteristics of the urban system, including size, industry, infrastructure and stage of development. For example, discharges from the wastewater sector are typically the largest phosphorus flow from the urban system, and the fate of those flows (landfill, agriculture, ocean, non-agricultural land) can vary widely. Qiao et al. [23] found that on average 55% of the excreted phosphorus from Beijing and Tianjin remained in sewage sludge, and that the largest share of this sludge was deposited in landfills. They also demonstrated that phosphorus recycling had decreased during recent years as a result of both economic and policy arguments such as the increased costs of sewage sludge transportation and quality measures in accordance with new regulations. Montangero et al. [22], Neset et al. [20] and Tangsubkul et al. [34] similarly point towards the low current rate of phosphorus recovery from wastewater and organic waste, and the large potential of phosphorus supply to agriculture through infrastructural changes that help to increase urban phosphorus recovery.
The global studies predominantly emphasised the emissions of environmental pollutants [26,27] during mining or fertiliser production, and losses from agriculture [21,28]. Cordell et al. [2] highlight that approximately 80% of phosphorus is lost between mine and fork at all stages of the food production and consumption system. Bouwman et al. [27] point out that to slow or decrease phosphorus use in the environment, proactive approaches towards the environmental consequences of phosphorus pollution can be effective in the long-term. Senthilkumar et al. [28] suggest that re-designing regional agricultural systems could contribute significantly to phosphorus use efficiency, for example, by reconstructing natural phosphorus flows as suggested by Liu et al. [21]. The main focus of the regional and national studies included food security, environmental protection and sustainable wastewater management. National scale SFAs mostly show that the largest phosphorus losses were leakage from agricultural land (e.g. up to 66% in the United States reported by Suh and Yee) [24] or as direct emissions from effluent wastewaters or solid waste [29,30]. However, several studies also showed that phosphorus losses from the food system via exported products could be significant, such as bone meal for porcelain and other uses from The Netherlands (27% of total exports) [31], or live sheep and cattle exports from Australia (approximately 30% of total losses) [18] or iron slag in Japan [32]. On a catchment level, the main focus is often the total nutrient load on the receiving water and the contribution from different sectors. A Helsinki Commission assessment report [33] focused on the nutrient loads to the Baltic Sea (such as diffuse emissions from agriculture and Current Opinion in Biotechnology 2012, 23:839–845
Discussion It is clear from recent phosphorus SFA studies reviewed in this paper, and from other relevant literature that the mass balance approach provides a mechanism that can be used to inform phosphorus management responses to both pollution and scarcity at a variety of scales (such as reducing losses). The research cited here demonstrates that in general the largest phosphorus losses tend to occur from mining inefficiencies, as diffuse discharges from agriculture, and in point source from the wastewater sector. However, cross-scale and cross-sectoral analyses are critical when identifying ‘hotspots’ for improved phosphorus management. While the mining and fertiliser production sector is important in terms of phosphorus losses and potential for increased efficiency and phosphorus recovery, it is excluded from most national (and regional) analyses because most countries are phosphorus rock and fertiliser consumers, while only few are producers. This system boundary problem can be overcome by linking regional and national studies to the ‘hinterland’ (the source of phosphate imports). Further, there is a need to explicitly include the food production and consumption sectors, and associated processes, to account for losses and inefficiencies from this extensive, but often-simplified chain, otherwise opportunities for www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 843
phosphorus recovery, reuse and increased efficiency can easily be overlooked. An important issue handicapping the effectiveness of the SFAs reviewed here (and stressed by Pellerin [19]) is data quality and availability. Without reliable, transparent and consistent data of phosphorus use, P-related exports, waste, among others, it is very difficult to accurately assess phosphorus stocks and flows, and to effectively direct phosphorus management actions or policy. While some data could potentially be collected centrally and transferred/utilised across study sites (such as the phosphorus content of crop types or specific manures) other data sets will need to be context specific (such as wastewater treatment processes and the phosphorus embodied in the associated waste flows). The review indicates that identifying ‘hotspots’ for phosphorus recovery or reuse is heavily dependent on the scale of analysis. For example, city-scale analysis may be most appropriate if the focus of an SFA study is improved wastewater management (and associated pollution). If pollution and leakage is the key focus, a catchment-scale analysis might suffice. National or global-scale analyses are most appropriate for studies addressing food security. This is exemplified by the case of Australia, where phosphorus in excreta represents less than 2–3% of the nation’s phosphorus fertiliser demand (and hence could not alone contribute to replacing phosphate rock as a phosphorus source). However, at the scale of Sydney city, the flow of phosphorus in treated wastewater to the ocean is by far the main loss of phosphorus from the system. Since system borders — and in particular the processes and flows — are individually defined to address each study’s research aim and context, studies (e.g. at the city scale) may not be directly comparable, despite strong similarities. This also restricts directly up-scaling or down-scaling studies to different geographical scales (although studies can certainly be linked via phosphorus flows to higher or lower scale systems). Additionally, variability in phosphorus stocks and flows between processes and study regions can be significant due to differences in key sectors or trade within regions. This highlights the importance of new national or regional studies to guide the most appropriate management responses in the region. While phosphorus SFAs are highly useful tools to help inform and prioritise decision-making, they are limited in the sense that they only address the quantitative dimension of the phosphorus challenge. Other important qualitative dimensions such as farmer livelihood security, dependence on imports and phosphorus geopolitics, effective governance, as well as synergies between sustainable phosphorus measures and other sustainability challenges [35] should also be assessed. Scientifically www.sciencedirect.com
robust methods for assessing risk and vulnerability through qualitative phosphorus vulnerability assessments (PVA) can complement SFAs by providing more integrated and complete assessments of the phosphorus challenge in a given context, and by guiding the development of appropriate adaptation strategies [35]. Further, because phosphorus SFAs are not in themselves decision-making processes, participatory processes that explicitly engage the perspectives, preferences and expertise of key stakeholders, informed by the SFA, are still required to effectively develop a roadmap to phosphorus security.
Conclusions While the size of individual phosphorus flows in SFAs varies from study to study, all recent phosphorus mass balances indicate substantial phosphorus losses and waste streams from the food production and consumption system to a greater or lesser extent. This indicates a need to both reduce losses and recover phosphorus effectively and efficiently. Key hotspots can be addressed through innovative technologies and systems, ranging from techniques that efficiently extract phosphorus from phosphogypsum waste piles during mining and fertiliser processing, to technologies that can recover phosphorus in an energy-efficient and cost-effective way from sanitation systems, while ensuring that the product is an effective and environmentally benign fertiliser. While recent literature includes most components of the food chain — from mine to fork and beyond — an evident need for a more integrated, qualitative approach to phosphorus management that includes stakeholder consultation, regional and national policy making, and more detailed phosphorus flow analyses through the food chain remains imperative.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
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Linko¨rping, Sweden, 1870–2000. Sci Total Environ 2008, 396:111-120. This city scale SFA study focused on the P flows in Linko¨rping, Sweden and its regional surrounding with a historical perspective from 1870 to 2000. It focussed on food production and consumption, as well as the historical changes in P recycling from urban waste. This study concluded that shifting from local recycling to a more linear flow of phosphorus through the system would be beneficial, and that the use of phosphorus fertiliser over this period had increased. 21. Liu Y, Villalba G, Ayres RU, Schroder H: Global phosphorus flows and environmental impacts from a consumption perspective. J Ind Ecol 2008, 12:229-247. This global SFA study takes a consumption perspective with particular focus on food production and phosphorus balances in the soil system. The study concludes that a significant net loss of phosphorus can be expected from the world’s crop lands under the current practices. The study suggests the reconstruction of the ‘physical structure of phosphorus flows’ to regulate the ‘societal P flows’. 22. Montangero A, Cau LN, Anh NV, Tuan VD, Nga PT, Belevi H: Optimising water and phosphorus management in the urban environmental sanitation system of Hanoi, Vietnam. Sci Total Environ 2007, 384:55-66. This city level SFA study focuses on both water and phosphorus flows. The study proposes changes to increase the recovery of phosphorus from waste products (e.g. replacing septic tanks with urine diversion latrines) as well as the increased production of fish, vegetables, beans and nuts instead of livestock. 23. Qiao M, Zheng Y-M, Zhu Y-G: Material flow analysis of phosphorus through food consumption in two megacities in northern China. Chemosphere 2011:774-778. The paper conducts a Substance Flow Analysis for two megacities (Beijing and Tianjin) for 2008, the SFA shows the large P input through the food production system and the low share of recycling. Fifty-five percent of the excreted P ends up in sewage sludge (most sewage sludge ends up in the landfill), while recycling has decreased during recent years due to both economic and policy issues. 24. Suh S, Yee S: Phosphorus use-efficiency of agriculture and food system in the US. Chemosphere 2011, 84:806-813. Phosphorus use efficiency is calculated for the United States based on a phosphorus accounting framework developed by the authors. The authors demonstrate that in the US, up to 85% of mined phosphorus is used in the provision of food, the rest being lost to the environment. Sixty-six percent of the loss occurs during meat and dairy production, and crop cultivation. Other losses occur in mining, the manufacture of fertilisers, and from household food waste. The authors note that data used in the research had questionable reliability. 25. Prud’Homme M: World phosphate rock flows, losses and uses. Phosphates 2010 International Conference; International Fertiliser Industry Association: 2010. 26. Villalba G, Liu Y, Schroder H, Ayres RU: Global phosphorus flows in the industrial economy from a production perspective. J Ind Ecol 2008, 12:557-569. This global phosphorus SFA focused on industrial P production, with a particular focus on efficiency, waste and environmental pollution in the mining of phoshate rock. The authors conclude that most of the consumed P ‘ends up as solid waste’, and that the current mode of consumption will lead both to possible depletion as well as to pollution (and ‘overburden’) of soil and water. Specific ways of optimising the resource use of P are presented with particular focus on waste minimisation during extraction and recovery of fluosilisic acid and gypsum. 27. Bouwman AF, Beusen AHW, Billen G: Human alteration of the global nitrogen and phosphorus soil balances for the period 1970–2050. Global Biogeochem Cycles 2009:23. The authors show that global variability in P soil balances are determined by total crop and livestock production, and by nutrient use efficiency. Under the Millenium Ecosystem Assessment scenarios, massive increases in P use are expected in developing countries. In countries with proactive approaches to environmental problems, P use shows a slower increase, or even a decline. 28. Senthilkumar K, Nesme T, Mollier A, Pellerin S: Regional-scale phosphorus flows and budgets within France: the importance of agricultural production systems. Nutr Cycl Agroecosyst 2011:1-15. A comparative study conducted with a regional focus in France that examined the relationship between phosphorus flows and agriculture. www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 845
The authors demonstrate that regional soil P budgets and the inflow (e.g. fertiliser) and outflow (e.g. livestock, dairy products) of soil P were strongly dependent on regional agricultural production systems. The authors suggest that redesigning regional farming systems could help to drive nutrient use efficiency at a global scale. 29. Yuan Z, Shi J, Wu H, Zhang L, Bi J: Understanding the anthropogenic phosphorus pathway with substance flow analysis at the city level. Journal of Environmental Management 2011, 92:2021-2028. This county level SFA study developed a P metabolic model to determine the magnitude and interrelations of P flows including the regional P fertilizer production. The study concludes that closing the urban-rural P cycle could mean that no more P from chemical fertiliser needs to be imported in to this region. Suggestions for improved efficiency include the reuse of industrial by-products, increased efficiency in fertiliser use and the recovery and reuse of manure and excreta. 30. Gumbo B: Short-cutting the phosphorus cycle in urban ecosystems. In Institute for Water Education. UNESCO-IHE; 2005. 31. Smit AL, Middelkoop JC, Dijk WV, Reuler HV, Buck AJD, Sanden PACM: A Quantification of Phosphorus Flows in the Netherlands through Agricultural Production, Industrial Processing and Households. Wageningen University; 2010:. Report 364.
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Current Opinion in Biotechnology 2012, 23:839–845
The phosphorus mass balance: identifying ‘hotspots’ in the food system as a roadmap to phosphorus security Dana Cordell1, Tina-Simone Schmid Neset2 and Timothy Prior1 Phosphorus is a critical element on which all life depends. Global crop production depends on fertilisers derived from phosphate rock to maintain high crop yields. Population increase, changing dietary preferences towards more meat and dairy products, and the continuing intensification of global agriculture supporting this expansion will place increasing pressure on an uncertain, but finite supply of high-quality phosphate rock. Growing concern about phosphorus scarcity and security, coupled with the environmental impact of phosphorus pollution, has encouraged an increase in research exploring how phosphorus is used and lost in the food system — from mine to field to fork. An assessment of recent phosphorus flows analyses at different geographical scales identifies the key phosphorus ‘hotspots’, for example within the mining, agriculture or food processing sectors, where efficiency and reuse can be substantially improved through biotechnological approaches coupled with policy changes. Addresses 1 Institute for Sustainable Futures, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia 2 Centre for Climate Science and Policy, Dept. of Water and Environmental Studies, Linko¨ping University, 601 74 Norrko¨ping, Sweden Corresponding author: Cordell, Dana ([email protected])
Current Opinion in Biotechnology 2012, 23:839–845 This review comes from a themed issue on Phosphorus biotechnology Edited by Andrew N Shilton and Lars M Blank For a complete overview see the Issue and the Editorial Available online 12th April 2012 0958-1669/$ – see front matter, # 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.copbio.2012.03.010
Introduction Phosphorus scarcity has gained increased attention on the research and policy agenda over recent years, partially due to the 800% phosphate rock price spike in 2008 [1,2,3,4]. However, actual estimates of phosphate depletion or peak phosphorus vary widely, from the critical point occurring in 30–40 years to 300–400 years [2,5–8]. These estimations diverge due to various reasons, ranging from the uncertainty in volume and quality of the global reserves, to the estimates of future demand (with the more optimistic studies assuming no growth in phosphorus demand). In addition to more comprehensive global analyses, there remains a need to assess regional and national vulnerability www.sciencedirect.com
to phosphorus scarcity in order to guide appropriate responses to ensure phosphorus security. Phosphorus security means ensuring access to sufficient phosphorus to produce enough food to feed the population, while at the same time restoring/maintaining ecological integrity and farmer livelihoods [10]. Phosphorus is required for food production and its consumption maintains vital human functions, such as transporting energy to the brain and building cell walls [9]. Humans require only approximately 1.2 g/person/day — amounting to three million tonnes of phosphorus per year for the global population. However, around fivefold this amount is mined annually to produce fertilisers for food production because of the substantial losses and inefficiencies in the global food system from mine to field to fork [2]. Achieving phosphorus security will require an integrated approach that combines supply-side technologies and strategies (such as recovering phosphorus from mine waste, food processing and sanitation waste streams for reuse in agriculture) with demand-side measures (such as increasing efficient use of phosphorus in fertiliser and food production or changing diets) [2,10]. However, there is currently insufficient baseline data on phosphorus in the food system (such as the distribution of organic sources of phosphorus from manure, excreta, food waste). Establishing a phosphorus mass balance for a given city, region or country using Substance Flow Analysis (SFA) allows scientists to estimate how phosphorus flows through the anthroposphere (‘human’ system), thereby assessing the potential contribution of such technologies and strategies. The magnitude of these flows varies widely between countries, underlining the importance of national or multi-scale analyses. As such, SFA is considered a fundamental tool for improved phosphorus management [11]. This article reviews existing phosphorus SFAs and assesses their scope, key findings and major phosphorus losses. From this analysis, generalisations, knowledge gaps and implications are noted, including an identification of the potential for sustainable biotechnology innovations that can respond to the phosphorus security challenge.
Phosphorus flow analysis Substance flow analysis (SFA): a tool for managing phosphorus
Since the early 1990s, Substance Flow Analysisa (SFA) has been used to examine resources such as water and a
Also referred to as Material Flow Analysis (MFA) [12]. Current Opinion in Biotechnology 2012, 23:839–845
840 Phosphorus biotechnology
Figure 1
EXPORT SYSTEM BOUNDARY NATURAL ENVIRONMENT (air, soil, water) ANTHROPOSPHERE Industry/ trade/ commerce
Waste management
Household
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IMPORT
LEGEND: material flux influenced by the market emissions from Anthropogenic sources geogenic fluxes
Current Opinion in Biotechnology
Conceptual substance flow analysis diagram showing the interactions between the ‘anthroposphere’ (human activity system) and the natural environment. Redrawn from Baccini and Brunner [17].
energy [13], metals and toxic substances [14,15] at a wide range of geographical scales (from global to local). The method was established in the field of Industrial Ecology to aid environmental management by assessing the ‘metabolism’ of human or technical systems, often referred to as the technosphere or anthroposphere [16,17]. The method is based on the principle of mass balance, which enables a systematic assessment and tracking of the flow of goods, materials or substances between various processes in the relevant sectors, as well as imports to and exports from the system that are typically measured in units of mass per year (Figure 1). SFAs can aid the identification of key flows or ‘hotspots’ of the substance under investigation, thereby facilitating more effective and prioritised management of the substance within that system. However, SFAs only provide a Current Opinion in Biotechnology 2012, 23:839–845
quantitative (rather than qualitative) picture, and data availability and reliability are often poor. Nutrients, and in particular phosphorus, have been the subject of many substance flow studies. The early focus of this work was primarily pollution and leakage, but has more recently shifted to assessments of scarcity and food security, as the latter issues have received increased attention [18,19,20]. A recent (July 2011) workshop focused on national-level phosphorus SFA studies [19] stressed that both pollution and scarcity aspects are important to include. The workshop demonstrated the need for an integrated assessment of phosphorus flows between sectors (such as fertiliser, food and sanitation sectors) at the national/regional scale in order to decrease losses and increase efficiency, recovery and reuse of phosphorus within the food system. www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 841
Assessment of recent phosphorus flow analyses
The matrix in Figure 2 presents the results of a review of 18 recent phosphorus SFA studies in terms of geographical and temporal coverage, scope (pollution, scarcity) and sectors of the food production-consumption system. Criteria used to select these papers included: post-2005 phosphorus SFAs articles; peer-reviewed; an equal spread of geographical scale (global, national, regional, city) and continents; articles that addressed pollution and scarcity; and multi-sectoral studies (i.e. covering the entire food
production/consumption system from mining through to food consumption and waste). The geographical scale of the reviewed articles ranged from city-wide phosphorus SFA studies to catchments, nations, regions and the global scale. Regardless of scale, the primary objective of most studies was environmental management of phosphorus, particularly through a focus on agricultural losses and waste management in the wastewater sector [21,22,23]. A majority of the most
Figure 2
Agriculture
Food production &
Household
Waste
Pollution and leakage
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City
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National
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Cordell et al. (2009)
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2005
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Liu et al. (2008)
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2005
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Villalba et al. (2008)
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Bouwman et al. (2011)
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20002050
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P SFA study
Schröder et al. (2010)
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19702000
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EU
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2006/7
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Shucheng county, China
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2008
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Japan
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2002
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Australia
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2007
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Turkey, Austria
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2001
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US
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~2007 -
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19902006
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2004
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2000
Yuan et al. (2011) Matsubae-Yokoyama et al. (2009)
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Cordell & White (2010)
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Seyhan (2009)
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Suh & Yee (2011)
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Senthilkumar et al. (2011)
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Smit et al. (2010) Gumbo (2005)
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Helsinki Commission (2005)
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Montangero et al. (2007)
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Neset et al. (2008)
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Sectors Mining & fertilizer production
Scope
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France The Netherlands
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Zimbabwe
Lake Chivero
Harare
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Baltic Sea
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Hanoi
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19802000 2000
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20012006
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Linköping
18702000
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Tangsubkul et al. (2005)
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Sydney
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2000
Qiao et al. (2011)
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Beijing, Tianjin
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2008
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Assessment of 18 recent phosphorus SFAs spanning different geographical scales, regions, scopes and sectors. www.sciencedirect.com
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recent studies included a discussion on phosphorus scarcity and explicitly highlighted opportunities for increased efficiency, recovery and reuse to meet the future challenges of phosphorus supply for food production [18,24]. Most studies noted low data reliability and the need for improved and standardised reporting.
livestock in Poland and wastewater discharges from diffuse and point sources) and emphasised the need for joint efforts between the Baltic Sea countries and improvement of agricultural practises (and development of associated policy measures) to reduce diffuse emissions from agriculture and other diffuse sources.
With respect to sectors, almost all studies analysed agriculture, household and wastewater sectors, and losses to the environment (water bodies). However, the processes between agriculture and household sectors were often collapsed into one box or flow (often termed ‘industry’) despite the food production, processing, trade and retail system being a long and complex chain resulting in substantial phosphorus losses in organic and food waste [10]. Similarly, phosphorus flows associated with mining, processing and fertiliser production were often not quantified despite recent estimates suggesting phosphorus losses in this subsystem may be substantial [10,25,26].
City level studies showed more variation in key phosphorus flows, largely since they represent the specific characteristics of the urban system, including size, industry, infrastructure and stage of development. For example, discharges from the wastewater sector are typically the largest phosphorus flow from the urban system, and the fate of those flows (landfill, agriculture, ocean, non-agricultural land) can vary widely. Qiao et al. [23] found that on average 55% of the excreted phosphorus from Beijing and Tianjin remained in sewage sludge, and that the largest share of this sludge was deposited in landfills. They also demonstrated that phosphorus recycling had decreased during recent years as a result of both economic and policy arguments such as the increased costs of sewage sludge transportation and quality measures in accordance with new regulations. Montangero et al. [22], Neset et al. [20] and Tangsubkul et al. [34] similarly point towards the low current rate of phosphorus recovery from wastewater and organic waste, and the large potential of phosphorus supply to agriculture through infrastructural changes that help to increase urban phosphorus recovery.
The global studies predominantly emphasised the emissions of environmental pollutants [26,27] during mining or fertiliser production, and losses from agriculture [21,28]. Cordell et al. [2] highlight that approximately 80% of phosphorus is lost between mine and fork at all stages of the food production and consumption system. Bouwman et al. [27] point out that to slow or decrease phosphorus use in the environment, proactive approaches towards the environmental consequences of phosphorus pollution can be effective in the long-term. Senthilkumar et al. [28] suggest that re-designing regional agricultural systems could contribute significantly to phosphorus use efficiency, for example, by reconstructing natural phosphorus flows as suggested by Liu et al. [21]. The main focus of the regional and national studies included food security, environmental protection and sustainable wastewater management. National scale SFAs mostly show that the largest phosphorus losses were leakage from agricultural land (e.g. up to 66% in the United States reported by Suh and Yee) [24] or as direct emissions from effluent wastewaters or solid waste [29,30]. However, several studies also showed that phosphorus losses from the food system via exported products could be significant, such as bone meal for porcelain and other uses from The Netherlands (27% of total exports) [31], or live sheep and cattle exports from Australia (approximately 30% of total losses) [18] or iron slag in Japan [32]. On a catchment level, the main focus is often the total nutrient load on the receiving water and the contribution from different sectors. A Helsinki Commission assessment report [33] focused on the nutrient loads to the Baltic Sea (such as diffuse emissions from agriculture and Current Opinion in Biotechnology 2012, 23:839–845
Discussion It is clear from recent phosphorus SFA studies reviewed in this paper, and from other relevant literature that the mass balance approach provides a mechanism that can be used to inform phosphorus management responses to both pollution and scarcity at a variety of scales (such as reducing losses). The research cited here demonstrates that in general the largest phosphorus losses tend to occur from mining inefficiencies, as diffuse discharges from agriculture, and in point source from the wastewater sector. However, cross-scale and cross-sectoral analyses are critical when identifying ‘hotspots’ for improved phosphorus management. While the mining and fertiliser production sector is important in terms of phosphorus losses and potential for increased efficiency and phosphorus recovery, it is excluded from most national (and regional) analyses because most countries are phosphorus rock and fertiliser consumers, while only few are producers. This system boundary problem can be overcome by linking regional and national studies to the ‘hinterland’ (the source of phosphate imports). Further, there is a need to explicitly include the food production and consumption sectors, and associated processes, to account for losses and inefficiencies from this extensive, but often-simplified chain, otherwise opportunities for www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 843
phosphorus recovery, reuse and increased efficiency can easily be overlooked. An important issue handicapping the effectiveness of the SFAs reviewed here (and stressed by Pellerin [19]) is data quality and availability. Without reliable, transparent and consistent data of phosphorus use, P-related exports, waste, among others, it is very difficult to accurately assess phosphorus stocks and flows, and to effectively direct phosphorus management actions or policy. While some data could potentially be collected centrally and transferred/utilised across study sites (such as the phosphorus content of crop types or specific manures) other data sets will need to be context specific (such as wastewater treatment processes and the phosphorus embodied in the associated waste flows). The review indicates that identifying ‘hotspots’ for phosphorus recovery or reuse is heavily dependent on the scale of analysis. For example, city-scale analysis may be most appropriate if the focus of an SFA study is improved wastewater management (and associated pollution). If pollution and leakage is the key focus, a catchment-scale analysis might suffice. National or global-scale analyses are most appropriate for studies addressing food security. This is exemplified by the case of Australia, where phosphorus in excreta represents less than 2–3% of the nation’s phosphorus fertiliser demand (and hence could not alone contribute to replacing phosphate rock as a phosphorus source). However, at the scale of Sydney city, the flow of phosphorus in treated wastewater to the ocean is by far the main loss of phosphorus from the system. Since system borders — and in particular the processes and flows — are individually defined to address each study’s research aim and context, studies (e.g. at the city scale) may not be directly comparable, despite strong similarities. This also restricts directly up-scaling or down-scaling studies to different geographical scales (although studies can certainly be linked via phosphorus flows to higher or lower scale systems). Additionally, variability in phosphorus stocks and flows between processes and study regions can be significant due to differences in key sectors or trade within regions. This highlights the importance of new national or regional studies to guide the most appropriate management responses in the region. While phosphorus SFAs are highly useful tools to help inform and prioritise decision-making, they are limited in the sense that they only address the quantitative dimension of the phosphorus challenge. Other important qualitative dimensions such as farmer livelihood security, dependence on imports and phosphorus geopolitics, effective governance, as well as synergies between sustainable phosphorus measures and other sustainability challenges [35] should also be assessed. Scientifically www.sciencedirect.com
robust methods for assessing risk and vulnerability through qualitative phosphorus vulnerability assessments (PVA) can complement SFAs by providing more integrated and complete assessments of the phosphorus challenge in a given context, and by guiding the development of appropriate adaptation strategies [35]. Further, because phosphorus SFAs are not in themselves decision-making processes, participatory processes that explicitly engage the perspectives, preferences and expertise of key stakeholders, informed by the SFA, are still required to effectively develop a roadmap to phosphorus security.
Conclusions While the size of individual phosphorus flows in SFAs varies from study to study, all recent phosphorus mass balances indicate substantial phosphorus losses and waste streams from the food production and consumption system to a greater or lesser extent. This indicates a need to both reduce losses and recover phosphorus effectively and efficiently. Key hotspots can be addressed through innovative technologies and systems, ranging from techniques that efficiently extract phosphorus from phosphogypsum waste piles during mining and fertiliser processing, to technologies that can recover phosphorus in an energy-efficient and cost-effective way from sanitation systems, while ensuring that the product is an effective and environmentally benign fertiliser. While recent literature includes most components of the food chain — from mine to fork and beyond — an evident need for a more integrated, qualitative approach to phosphorus management that includes stakeholder consultation, regional and national policy making, and more detailed phosphorus flow analyses through the food chain remains imperative.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
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2.
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4.
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imported phosphate rock, P fertilisers, and hence vulnerable to future phosphorus scarcity and geopolitical fluxes around P exporting countries. Further, this study shows more P flows through the livestock sector than the arable sector. 5.
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Linko¨rping, Sweden, 1870–2000. Sci Total Environ 2008, 396:111-120. This city scale SFA study focused on the P flows in Linko¨rping, Sweden and its regional surrounding with a historical perspective from 1870 to 2000. It focussed on food production and consumption, as well as the historical changes in P recycling from urban waste. This study concluded that shifting from local recycling to a more linear flow of phosphorus through the system would be beneficial, and that the use of phosphorus fertiliser over this period had increased. 21. Liu Y, Villalba G, Ayres RU, Schroder H: Global phosphorus flows and environmental impacts from a consumption perspective. J Ind Ecol 2008, 12:229-247. This global SFA study takes a consumption perspective with particular focus on food production and phosphorus balances in the soil system. The study concludes that a significant net loss of phosphorus can be expected from the world’s crop lands under the current practices. The study suggests the reconstruction of the ‘physical structure of phosphorus flows’ to regulate the ‘societal P flows’. 22. Montangero A, Cau LN, Anh NV, Tuan VD, Nga PT, Belevi H: Optimising water and phosphorus management in the urban environmental sanitation system of Hanoi, Vietnam. Sci Total Environ 2007, 384:55-66. This city level SFA study focuses on both water and phosphorus flows. The study proposes changes to increase the recovery of phosphorus from waste products (e.g. replacing septic tanks with urine diversion latrines) as well as the increased production of fish, vegetables, beans and nuts instead of livestock. 23. Qiao M, Zheng Y-M, Zhu Y-G: Material flow analysis of phosphorus through food consumption in two megacities in northern China. Chemosphere 2011:774-778. The paper conducts a Substance Flow Analysis for two megacities (Beijing and Tianjin) for 2008, the SFA shows the large P input through the food production system and the low share of recycling. Fifty-five percent of the excreted P ends up in sewage sludge (most sewage sludge ends up in the landfill), while recycling has decreased during recent years due to both economic and policy issues. 24. Suh S, Yee S: Phosphorus use-efficiency of agriculture and food system in the US. Chemosphere 2011, 84:806-813. Phosphorus use efficiency is calculated for the United States based on a phosphorus accounting framework developed by the authors. The authors demonstrate that in the US, up to 85% of mined phosphorus is used in the provision of food, the rest being lost to the environment. Sixty-six percent of the loss occurs during meat and dairy production, and crop cultivation. Other losses occur in mining, the manufacture of fertilisers, and from household food waste. The authors note that data used in the research had questionable reliability. 25. Prud’Homme M: World phosphate rock flows, losses and uses. Phosphates 2010 International Conference; International Fertiliser Industry Association: 2010. 26. Villalba G, Liu Y, Schroder H, Ayres RU: Global phosphorus flows in the industrial economy from a production perspective. J Ind Ecol 2008, 12:557-569. This global phosphorus SFA focused on industrial P production, with a particular focus on efficiency, waste and environmental pollution in the mining of phoshate rock. The authors conclude that most of the consumed P ‘ends up as solid waste’, and that the current mode of consumption will lead both to possible depletion as well as to pollution (and ‘overburden’) of soil and water. Specific ways of optimising the resource use of P are presented with particular focus on waste minimisation during extraction and recovery of fluosilisic acid and gypsum. 27. Bouwman AF, Beusen AHW, Billen G: Human alteration of the global nitrogen and phosphorus soil balances for the period 1970–2050. Global Biogeochem Cycles 2009:23. The authors show that global variability in P soil balances are determined by total crop and livestock production, and by nutrient use efficiency. Under the Millenium Ecosystem Assessment scenarios, massive increases in P use are expected in developing countries. In countries with proactive approaches to environmental problems, P use shows a slower increase, or even a decline. 28. Senthilkumar K, Nesme T, Mollier A, Pellerin S: Regional-scale phosphorus flows and budgets within France: the importance of agricultural production systems. Nutr Cycl Agroecosyst 2011:1-15. A comparative study conducted with a regional focus in France that examined the relationship between phosphorus flows and agriculture. www.sciencedirect.com
The phosphorus mass balance Cordell, Neset and Prior 845
The authors demonstrate that regional soil P budgets and the inflow (e.g. fertiliser) and outflow (e.g. livestock, dairy products) of soil P were strongly dependent on regional agricultural production systems. The authors suggest that redesigning regional farming systems could help to drive nutrient use efficiency at a global scale. 29. Yuan Z, Shi J, Wu H, Zhang L, Bi J: Understanding the anthropogenic phosphorus pathway with substance flow analysis at the city level. Journal of Environmental Management 2011, 92:2021-2028. This county level SFA study developed a P metabolic model to determine the magnitude and interrelations of P flows including the regional P fertilizer production. The study concludes that closing the urban-rural P cycle could mean that no more P from chemical fertiliser needs to be imported in to this region. Suggestions for improved efficiency include the reuse of industrial by-products, increased efficiency in fertiliser use and the recovery and reuse of manure and excreta. 30. Gumbo B: Short-cutting the phosphorus cycle in urban ecosystems. In Institute for Water Education. UNESCO-IHE; 2005. 31. Smit AL, Middelkoop JC, Dijk WV, Reuler HV, Buck AJD, Sanden PACM: A Quantification of Phosphorus Flows in the Netherlands through Agricultural Production, Industrial Processing and Households. Wageningen University; 2010:. Report 364.
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32. Matsubae-Yokoyama K, Kubo H, Nakajima K, Nagasaka T: A material flow analysis of phosphorus in Japan: The iron and steel industry as a major phosphorus source. Journal of Industrial Ecology 2009, 13:687-705. This detailed P SFA found that for Japan, a country totally dependent on P imports, the amount and concentration of P in iron and steel-making slag is comparable to that in imports, presenting an opportunity for efficient P recovery form this sector. 33. Helsinki Commission: Nutrient pollution to the Baltic Sea in 2000. In . No. 100 Baltic Sea Environment Proceedings. 2005:1-24. Assessment report on the nutrient loads to the Baltic Sea. Concludes with a general overview of recommendations emphasising the need for joint efforts around the Baltic Sea, improvement of agricultural practises to reduce diffuse emissions, as well as the development of policy measures. 34. Tangsubkul N, Moore S, Waite TD: Incorporating phosphorus management considerations into wastewater management practice. Environ Sci Policy 2005, 8:1-15. This city-scale P SFA focusing on wastewater management found that of the 50% of imported P that leaves Sydney, 90% is exported to the ocean via treated wastewater discharges. Policy scenarios reveal P separation at source enabling beneficial agricultural reuse, and behaviour change (e.g. diets) are likely to be the most effective policy options. 35. Neset T-SS, Cordell D: Global phosphorus scarcity: identifying synergies for a sustainable future. Sci Food Agric 2012, 92:2-6.
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