Recycling phosphorus from our food scraps and other organic waste is important for two reasons:
1. World reserves of phosphorus for making phosphorus fertilizer are finite – estimates suggest 35 to 300 years.
2. Phosphorus fertilizers contain heavy metals and radionuclides that we are importing onto our farms.
Many communities are working diligently to reduce waste to landfill by establishing waste to energy and composting facilities. After we divert the organic waste from landfill and produced compost, what do we do with it? Many communities are considering using the compost in their own communities, for community beautification projects. This is a great idea, but let us also consider phosphorus recycling, and the need to return phosphorus for agricultural production.
Phosphorus is essential to all of life – particularly for our DNA and energy transport systems in plants, animals and microbial life. There is no substitute for phosphorus. We began mining phosphorus reserves starting around WWII to produce phosphorus fertilizer. Phosphorus is one of the three main fertilizer nutrients required for plant growth. Most fertilizers that we purchase contain phosphorus (its the P in N-P-K fertilizers).
Phosphorus is a finite element. Although it is the 11th most abundant element in the earth’s crust, rock containing significant concentrations of phosphorus is limited. Some estimates suggest that world phosphate reserves will be depleted in 35 to 350 years, depending on the author and the study (Cordell and White 2011, Cummins 2014).
Regardless of how many years our phosphorus reserves will last, we have to understand that our phosphorus reserves are contaminated with heavy metals and radionuclides. We see reports of agricultural land in China that can no longer be used for agriculture because it is too contaminated with cadmium and lead (http://www.vancouversun.com/technology/Vast+tracts+land+polluted+crops+official+says/9337103/story.html) Some of this contamination is from using phosphate rock. On average, worldwide, phosphate rock contains an average of 25 ppm cadmium, 188 ppm chromium and 10 ppm lead (Kongshaug et al. 1992).
Phosphate rock also contains radionuclides. The average uranium content in phosphate rock is 50-200 ppm (Ragheb and Khasawneh 2010). It is not economically practical to remove the uranium during the production of phosphorus fertilizers, hence it remains in the fertilizer. During phosphorus fertilizer manufacturing, approximately 5 tonnes of phosphogypsum is produced per tonne of phosphoric acid fertilizer (LeMone et al. 2009). This phosphogypsum contains radium, a radioactive decay product of uranium. Most experts will suggest that the radioactivity is below the recommended limits.
Until recently, I did not realize the presence and impact of radionuclides present in phosphate rock. The tobacco industry learned already in the 1950s that phosphate rock produced the best tobacco. Cigarettes contain radioactive material, particularly lead 210 and polonium 210, which concentrates in the lungs (www.epa.gov/radiation/sources/tobacco.html, www.nuc.berkeley.edu/forum/218/radioactive-tobacco.2012-07-15). The last website suggests that the level of radiation absorbed by a 1.5 pack per day smoker is equivalent to at least 300 chest x-rays per year!
Based on the limited availability of phosphate rock, and the contamination by heavy metals and radionuclides, we should be making our best efforts to recycle phosphorus in our food production systems.
Only 15% of the total phosphorus extracted from nature for the provision of food is eventually ingested by humans (Suh and Yee 2011). Of the remainder, an estimated 66% is lost to the environment during food production. A significant portion of the remainder is in the discarded foodwaste. This is the portion that we can recover during our organics diversion from land-fill to improve the life-cycle phosphorus use efficiency. However, this means that we have to consider recycling the phosphorus back into agriculture for food production, rather than simply over supplying our compost (and phosphorus) to our roadsides!
Cordell, D., and S. White. 2011. Peak phosphorus: clarifying the key issues of a vigorous debate about long-term phosphorus security. Sustainability 3: 2027-2049
Cummins, J. 2014. Phosphorous Starvation Threatens the World. Institute of Science in Society. ISS Report 11/01/14. http://www.i-sis.org.uk/Phosphorus_Starvation_Threatens_the_World.php.
Kongshaug et al. 1992. Cited in Mortvedt, J.J. and J.D Beaton, 1995. Heavy metal and radionuclide contaminants in phosphorus fertilizers. Chapter 6 in Phosphorus in the Global Environment. H. Tiessen, ed. J. Wiley & Sons Ltd.
LeMone, D.V., P.C. Goodell, A.H. Harris and J.W. Winston. 2009. Phosphate Rocks: Sustainable secondary source for uranium and their agricultural impact. WM2009 Conference, March 1-5, 2009. Phoenix, AZ.
Ragheb, M. and M. Khasawneh. 2010. Uranium fuel as byproduct of phosphate fertilizer production. Proceedings of the 1st International Nuclear and Renewable Energy Conference, Amman, Jordan, March 21-24, 2010.
Suh, S., and S. Yee. 2011. Phosphorus use efficiency of agriculture and food system in the US. Chemosphere 84: 806-813.