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Large amounts of phosphorus get into the water via fertilizers | The Phosphorus Crisis

The focus is mostly on plastic or metal - but there is another raw material that urgently requires saving and recycling: phosphorus.

Saving and recycling phosphorus.
Saving and recycling phosphorus.

The worldwide stocks of this plant nutrient are limited and are increasingly used up for fertilizer production. Now researchers are focusing on a previously neglected cause of waste: aquaculture. 

The unsustainable use of phosphorus in fish farming should be restricted in order to ensure the long-term food security of mankind.

The shift of phosphorus transfers in global fisheries and aquaculture, chart.
The shift of phosphorus transfers in global fisheries and aquaculture.

Nothing works without phosphorus 

The element (phosphorus) plays a central role in many building blocks and processes of life. 

This becomes particularly clear with plants: without this nutrient they cannot grow. 

In order to optimize the yields in crop production, an adequate supply of phosphorus via fertilization is necessary. 

For a long time, however, there was a tough mentality: According to the motto "a lot helps a lot", wasteful amounts of phosphorus were applied to fields. 

In addition to the negative consequences for ecological balances in nature, this is problematic for another reason: Phosphorus is not available indefinitely - global supplies are running out.

A phosphorus crisis is emerging

In 2014, the European Union therefore included phosphorus in the list of 20 critical raw materials whose security of supply is at risk and whose economic importance is high. 

As a result, regulations for the use of phosphorus fertilizers were introduced, which should ensure increased efficiency in agricultural production. 

Above all, the aim is to prevent excess phosphorus - not used by plants - from ending up in water. 

However, it is optimal if the phosphorus is bound in the plant material and ends up in the field again at the end of the food chain - recycling is the motto.

In this context, an international team of researchers is now focusing on the previously neglected use of phosphorus in aquaculture. 

They systematically recorded the phosphorus consumption in fish farming worldwide and analyzed where the nutrient ends up. 

As they explain, the difference to fishing for wild fish is that they meet their phosphorus needs from naturally occurring food sources such as other fish or plankton. 

Human consumption of fish creates a phosphorus flow from the sea to the land. 

In contrast, aquaculture relies on the addition of phosphorus in the fish feed or in order to stimulate the growth of plants that serve the fish as feed.

Loss of phosphate from land to water

In this context, as the researchers report, the results of their investigations show that fish farming worldwide consumes significant amounts of phosphorus with very little efficiency.

This means that only about a quarter of the phosphorus used to raise the fish accumulates in the animals and is fed into the terrestrial material cycle through the later consumption of the animals. 

“The phosphorus that gets into rivers and oceans can be considered lost because it is extremely difficult to recover. Such losses should be avoided as much as possible to ensure that enough phosphorus is also available for future generations, ”explains co-author Daniel Goll from the University of Augsburg.

The sustainability factor

Against the background of the growing importance of breeding fish or shellfish in aquaculture, there is a significant sustainability problem, the researchers say. 

The proportion of aquaculture animals for human consumption rose from less than five percent in the 1950s to about 50 percent in the 2010s. 

The earlier phosphorus flow towards land from fishing has now turned into a loss of phosphorus from land to sea in the form of fertilizers and animal feed, the scientists emphasize.

“Phosphorus is a non-renewable, limited, and vital nutrient for crops and animals. We should think about how we can recycle and reuse phosphorus in the fishing industry to grow more crops.
At the same time, we should reduce the phosphorus that we put into the water in aquaculture to a minimum, ”says co-author Yuanyuan Huang from the Paris-Saclay University in Gif-sur-Yvette.

Source: University of Augsburg, technical article: Nature Communications.