Phosphorus is a critical resource underlying global agricultural production. This nutrient, a common component of commercial fertilizers, is essential for photosynthesis and the storage and transportation of energy in crops. This element is a critical component of global food security.

Unfortunately, global reserves of available phosphorus are limited. Unlike nitrogen, which can be synthesized from the atmosphere by either biological or industrial processes, there are no easy options for manufacturing phosphorous. As it stands, most phosphorous included in commercial fertilizers is mined, with small amounts being provisioned through manure and similar amendments. As with many mineral resources, we are approaching a future where available supplies run out. Current estimates place ‘peak phosphorus’ at around the middle of the century. So, while we have some time to install technologies to capture and recycle phosphorous, it is incumbent that we begin now.

To better understand the issues behind contemporary phosphate consumption, it’s useful to map the nutrient supply chain. The mineral is mined and applied to the field as fertilizer. After this, it ends up in one of three locations. It’s either drawn up into the crop biomass or soil flora, where it continues to cycle between the crops and soil during the next cycle, is lost in the water table, or sequestered in the food harvested from the field. From there, the phosphorus ends up in our food supply and, ultimately, global sanitation systems.

While in natural ecosystems phosphates cycle between pools, the human system is decidedly linear. Once the phosphorus ends up in the water table it is outside of our use. There are no pools anywhere along the phosphorous cycle where we can economically recover this valuable nutrient. With mineral supplies slowly dwindling, it is incumbent upon us to bend this linear pattern into a circular one. To establish a global phosphorous recovery and redistribution system.

Infrastructural improvements are necessary to capture phosphorous before it leaves human-managed systems. In wastewater treatment plants, various chemical or biological processes are available to precipitate phosphorus from the waste stream and capture it in a solid form that can then be processed for use as a fertilizer. Installing these across our water infrastructure to capture as much phosphorous as possible is vital for recovery.

While we broadly know the types and scales of infrastructure that must be established, coordinating such an effort is a daunting task. Governments can certainly fund such a build-out, but the outlays would be expensive and tie up a lot of federal and municipal capacity, especially given all of the other important infrastructural improvements our water and sanitation systems require. We could subsidize private actors to do the work for us, but that’s also quite expensive and comes with various skewed incentives (waste, fraud, etc.). As it stands, these solutions are quite expensive and require a lot of government capacity to function.

An alternative policy, however, could incentivize the creation of phosphorus recovery systems while minimizing the need for large budgetary allocations. An extraction tax is a consumption tax levied on the extraction of raw materials from the Earth. Currently, the price to mine phosphorus is far lower than the cost to recycle it, the economics of reclamation don’t pencil out without prodigious subsidies. An extraction tax could theoretically drive up the price of mining phosphorus and make alternative sources more attractive to the market.

Theoretically, such a policy would be incredibly difficult to put into place. Minerals are difficult to differentiate from one another. There is no clear difference between a product mined from Earth vs. one reclaimed from sewers, at least in a way that would be legible to a scaled tax collection system. The potential for fraud would be immense. In practice, however, implementing a phosphorus extraction tax would be simple due to the structure of the market. Only a handful of countries produce phosphate rock, with China and Morocco leading the market. For nations with little to no domestic production, a levy on production could be accomplished by a simple tariff. For those with a moderate level of domestic production, tax collection facilities can be established at the mines themselves to ensure proper payment. Revenues from such taxes should be diverted to municipal grants to build out reclamation infrastructure.

While there are no major existing extraction taxes to compare this proposal to, a study assessing similar a policy for lithium has yielded some important considerations. Their primary conclusions are that a tax on waste levied at the landfill level is the best way to drive lithium recycling, but since phosphorous has a more distributed waste pattern, the optimal solution is a tax subsidy scheme. While standalone recycling subsidies do raise reclamation rates, they don’t seem to have much impact on extraction rates. Pairing the cost of extraction with an incentive for recycling seems to optimize circularity.

Some important considerations should be explored before such a policy is put into place. The first is possible impacts on the price of food. Recent events have shown how disruptive fertilizer price shocks can be on global food prices, especially for the world’s most vulnerable. Any policy designed to increase the price of such a critical agricultural input should be implemented slowly, with incremental increases over time to minimize price spikes and to allow producers time to adjust production practices to utilize their fertilizers more efficiently or to identify recycled sources of the nutrient. Additionally, while the process of capturing phosphorous from wastewater is achievable at scale, there are no viable methods for capturing phosphorous loss in the field and bringing it back into the fertilizer chain. This is an area where minimizing fertilizer loss and increasing efficiency is of greater importance in comparison to reclamation and recycling, meaning an extraction tax is less helpful in driving improved practices. This policy is not the final solution for the phosphorous crisis, but merely a step towards resource circularity.

All-in-all, a combination of extraction taxes and recycling subsidies should be explored more for their potential to drive the transformation of our economy from linear to circular resource use. It is an important and underexplored policy that has great potential to lead us to a truly sustainable economy.

Teaser image credit: Mining of phosphate rock in Nauru. By Lorrie Graham/AusAID, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=32164905