Phosphorus Footprint, Our Diet and Environment

We have often talked about carbon footprint and its effect on the environment. Heard of phosphorus footprint?   What has this to do with our diet and the environment?

With the eminent festive season of eating, merrymaking and togetherness, here are some gentle reminders so that we do not overindulge.

Research has demonstrated that the impact of our dietary choices on the global phosphorus footprint is cause for concern.  As a start, a slight shift towards a more plant-based diet may be worth our considering.

Dietary Changes and Phosphorus Footprint
According to a study by researchers at McGill University published online in Environmental Research Letters (Source: http://iopscience.iop.org/1748-9326/7/4/044043), out dietary changes since the early 1960's have caused a sharp increase in the amount of mined phosphorus used to produce the food.  Between 1961 and 2007, rising meat consumption and total calorie intake resulted in a 38 percent increase in the world's per capita "phosphorus footprint."  Different food types require different amounts of phosphorus in their production. One kg of phosphorus can for example be used to either produce 3333 kg of starch roots (e.g. potatoes) or 16 kg of beef.

Mined phosphorus – a non-renewable energy and its impact
Mined phosphorus is a non-renewable resource that is widely used as fertilizer and critical in food production. Mined phosphate rock is becoming increasingly scarce which poses a severe problem to the farming industry.  In addition, uneven global deposits affecting its supplies and prices have caused geopolitical tensions. The findings also show that when phosphorus is lost through agricultural runoff or sewage systems via human excreta, it can pollute waterways downstream.  It can cause severe water quality degradation leading to eutrophication, harmful algal blooms, and impairment of our drinking water, recreational areas, and fisheries.

What is the Phosphorus Footprint?
A study by the Illinois Institute of Technology (Source: https://www.researchgate.net/publication/272203710_What_is_Your_Phosphorus_Footprint ) showed that the global phosphorus footprint   due to human activity is estimated to be somewhere in the range 2–14 Trillion g/yr. Compared to the global phosphorus footprint, wastewater contributes approximately 10% of this, i.e. 1.5 Tg/yr. In contrast, wastewater treatment contributes less than one percent of the global carbon footprint.  The net flow of material into or out of any system can be determined using the Life cycle assessments (LCA). Thus this technique can be used to assess the phosphorus footprint for any of these options - treatment, reclamation, or biosolids processing.  An example is presented to show that the phosphorus footprint of a wastewater treatment plant is reduced as it removes more phosphorus from the effluent and that using phosphorus recovery can reduce the footprint still-further.

Sustainable Strategy
The challenge is to manage the mined phosphorus supply in order to ensure its long-term sustainability and a resulting sustainable food system.

A two prong strategy is needed:

  1. The Illinois study showed that of all environmental impacts, the removal and reuse of phosphorus is the most significant consideration for wastewater treatment facilities. Recycling and reusing phosphorus by turning it into fertilizer or compost for agricultural use from food and human waste is the right step in deploying this valuable resource.
  2. An equally important strategy that is very much within our control is dietary choices and, especially the consumption of meat. The McGill study found the significant impact of diet changes can have on phosphorus fertilizer requirements and the importance of dietary choices in planning for a sustainable food system.  A reduction of meat intake can significantly reduce the demand for mined phosphorus as it takes many more kilograms of feed fertilized by phosphorus to produce a kilogram of meat. The study found that a switch to a plant-based diet of pulses (i.e. beans or legumes) from meat, dairy, eggs, and seafood food groups. Their calculations showed that a shift towards a plant-based diet would lead to a small increase of 8% in phosphorus excreted by the city residents. A big effect, on the other hand, was found when looking at the change in the residents' phosphorus footprint: a decrease of 72%. A good start would be to reduce meat dishes and have more vegetarian dishes this festive season. Many vegetarian options and recipes can be found online.