India is running out of phosphorus. Does the solution lie in our sewage? Premium

Phosphorus is a non-renewable resource that we are rapidly running out of. This is a big problem because it is an essential ingredient in fertilisers – even as it is a major pollutant. We must address both problems with systemic change, not incremental steps.

The problem with the fertilisation of land is as old as agriculture itself. When early humans first began to engage in settled agriculture, they quickly realised that while crops require nutrients for their growth, repeated cycles of cultivation and harvest depleted these nutrients, reducing yield over time. Early agricultural societies began to notice that certain areas produced better crops and that soils could be replenished.

This observation led to practices to restore essential nutrients in the soil necessary for plant and crop growth. Indigenous communities around the world developed methods of fertilisation, for example, using fish remnants and bird droppings (guano) as fertilisers.

This changed in the 19th century, which saw significant advancements in chemistry, leading to the creation of synthetic fertilisers as well as the identification of nitrogen, phosphorus, and potassium. They’re the foundation of modern synthetic chemical fertilisers and have caused agricultural productivity to boom. The Green Revolution of the mid-20th century accelerated the adoption of high-yield crop varieties and intensive use of these fertilisers, and today these substances are crucial to sustain global food production.

But we now have a problem. Phosphorus is scarce and exists only in limited quantities, in certain geological formations. Not only are we running out of it, it also pollutes the environment. It doesn’t exist as a gas, which means it can only move from land to water, where it leads to algal blooms and eutrophication.

The history of phosphorus spans its discovery in guano to current global supply chains. Today, a handful of countries control most of the world’s reserves of phosphorus. This is a major geopolitical concern. The world’s largest reserves are in Morocco and the Western Sahara region. But here, phosphorus coexists with cadmium, a heavy metal that can accumulate in animal and human kidneys when ingested. Removing cadmium is also an expensive process.

As a result, cadmium-laden fertilisers are often applied to the soil, absorbed by crops, and consumed, bioaccumulating in our bodies. Studies have found that this accelerates heart disease. In 2018, the EU passed new legislation to regulate cadmium levels in fertilisers.

Only six countries have substantial cadmium-free phosphorous reserves. Of them, China restricted exports in 2020 and many EU countries no longer buy from Russia. So the market for safe phosphorus has suddenly exploded. This is one reason why Sri Lanka banned the import of synthetic fertilisers and went organic in 2021, later experiencing a sudden drop in crop yield that precipitated a political crisis.