The importance of P: a ‘phosphorus week’ Q&A with Dr. Brooke Mayer

For many, phosphorus is just a reminder of their last chemistry class and the capital “P” floating below nitrogen on the periodic table. Prices for phosphorus do not tower above gas stations on brightly lit signs, and the element is almost never a point of discussion for news outlets, politicians, and public figures. Dr. Brooke Mayer, professor of civil, construction and environmental engineering at Marquette, wants to change that. For Mayer and others in the know, the individual, local and global stakes around this underappreciated element are a lot higher – so much so that Mayer and collaborators around the country have begun celebrating “phosphorus week (P-Week)” every April to raise awareness.

For the average citizen, there is a lot to discover about phosphorus’ role in their daily life. It is a daily part of most diets. Beyond our individual plates, it is used as fertilizer to support global food supply. It also serves as a potential pollutant when not managed properly, specifically in water sources we depend on for recreation and drinking water. These benefits and risks are complicated by it being a finite global resource that only a handful of countries have a grip on. All countries need it, not all countries have it, and it is not renewable outside of the slow creation of new rocks on the geologic time scale.

At Marquette, Mayer is doing her part to raise public awareness around phosphorus and develop engineering solutions that can alleviate some of the environmental and economic risks emerging around this underappreciated natural resource. Beginning in 2021, Mayer was awarded a $627,000 subaward as a partner in the National Science Foundation Science and Technology Center – Science and Technologies for Phosphorus Sustainability (STEPS), a five-year, $25 million initiative led by North Carolina State University. STEPS is a national research effort to reduce both dependence on mined phosphates and the amount of phosphorus that leaches into soil and water.

As part of STEPS, Mayer is leading efforts focused on improving phosphorus removal and recovery from wastes by 1) designing nature-inspired materials that can improve our ability to extract phosphorus from water/wastewater and recover it in a form amenable to reuse, i.e., as agricultural fertilizer, and 2) assessing the range of phosphorus chemical forms present in water/wastewater and the role of transformations of those chemical forms into chemical forms that facilitate phosphorus removal, recovery, and agricultural use.

In a Q&A, Mayer discusses the latest developments in her work and what the public might need to know about phosphorus.

Can you share some of the big-picture goals related to phosphorus that you and your collaborators in STEPS have?

Phosphorus is an interesting element in that it is paradoxically in too low of supply — it is a finite, irreplaceable resource used in food production — and in too high of supply — excess levels cause degradation of environmental waters, leading to human and environmental health concerns. So, there are multiple problems being solved at the same time.

The STEPS vision is to facilitate a 25% reduction in human dependence on mined phosphates and a 25% reduction in losses of phosphorus to soils and water resources within 25 years, leading to enhanced resilience of food systems and reduced environmental damage.

These goals are very ambitious, and our STEPS director, Dr. Jacob Jones, often compares this to a “moonshot,” reflective of the common President Kennedy quote, “We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard.”

What have been some of the recent milestones in your work with STEPS?

My team has developed and patented a protein-based material that is able to effectively and selectively capture phosphorus from complex waste streams. Following the capture, the phosphorus then goes through a controlled release into a concentrated, pure form that can then be reused. This solution is exciting as we are reducing the environmental pollutant and recycling it for its beneficial uses.

Another problem area that I am working on is related to the different forms that phosphorus can take in our environment. Some forms are a lot harder for people to remove and reuse, and are even difficult to access for natural plant life and microorganisms that uptake phosphorus. We are now researching different chemical and biological processes that could potentially be used to transform some of the more challenging forms of phosphorus into easier-to-work-with chemical forms.

Through the combined efforts of researchers at Marquette, the wider STEPS team, and collaborators across the country we are tackling phosphorus problems by leveraging many angles and disciplines. And of course, the public awareness around phosphorus is a common focus for all of us.

For the average citizen, what do you think is the most apparent phosphorus challenge?

The most visible aspect of phosphorus management for the average citizen is likely related to phosphorus’ identity as a pollutant. Excess levels of phosphorus in environmental waters stimulate the overgrowth of algae, which can manifest as the large green or red algae blooms that are prevalent in numerous fresh and ocean waters in summer months. These blooms have multiple negative impacts that are more widely discussed, but people seldom make the connection to phosphorus. One impact is the overabundance of algae depletes the dissolved oxygen in the water, which can cause water odors, and in some cases, large fish kills.

These blooms can also produce toxins that are dangerous to humans and animals. For example, we sometimes see warnings at local Wisconsin ponds about not letting pets swim in them to avoid exposure to toxins. In 2014, a major bloom of toxin-producing algae in Lake Erie led to the shutdown of Cincinnati’s drinking water supply.

The annual economic damages associated with these types of issues is estimated to be at least $2.2 billion annually in the U.S., a major portion of which is attributed to economic losses in lakefront property values. Left unabated, phosphorus pollution in waterways will continue to be exacerbated in coming years.

You touched on the economic impact of phosphorus as a pollutant. What are other economic stakes around phosphorus that the average citizen might not know?

Beyond the impacts of phosphorus pollution in environmental waters, phosphorus has a dual identity as a necessary input to global food production. The average citizen is not likely to notice this on a daily basis but can nonetheless be heavily impacted by phosphorus production and supply chains. For example, a number of factors combined to lead to a substantial increase in the price of rock phosphorus fertilizer in the wake of the 2008 financial crisis, and post-COVID-19 pandemic disruptions to phosphate production and distribution again increased the prices. Price increases are born by agricultural producers, and eventually passed along to consumers.

It is important to note that phosphorus reserves are geographically limited. Only six countries control 86% of phosphate reserves.

This is a finite, irreplaceable input into global food supplies. Accordingly, just like fossil fuels, there is a “peak production” time when it will not be economically feasible to extract phosphate rock for use as fertilizer. The time to this peak is a hotly debated subject that is necessarily based on a lot of projections about available reserves around the world. Although some reports have suggested that the time to peak phosphorus may be decades away, it currently seems more likely that it is several hundred years out. While this is fantastic news for us now, it does little to alleviate the unavoidable outcome that at some point in the future, available minable supplies will not meet demands. Just like fossil fuels, phosphate rock does regenerate, but it is unfortunately on a geologic timescale of 1000s of years.

As part of STEPS, we recently submitted an article focused on phosphorus supply vulnerability and resilience to shocks at scales ranging from local to global. We explore, for example, what would happen to phosphorus fertilizer supplies, and thus the global food market, in the face of low likelihood, but high impact events, such as extreme weather and natural disasters, pandemics, and geopolitical instability. We describe how understanding the interdependencies in the phosphorus supply system is paramount for enhancing critical infrastructure related to the global food supply.

While you and your collaborators use your expertise to create solutions around phosphorus, is there anything the average citizen can do?

Absolutely, which is why elevating phosphorus sustainability in the public consciousness is part of our STEPS Roadmap Toward Phosphorus Sustainability. Behavioral changes at an individual level, such as practicing a more plant-focused diet or composting, can directly decrease demand for phosphorus as well as losses of phosphorus to landfills or soils. Individuals can also be proactive about choices that lead to less phosphorus pollution in waterways. For example, urban runoff can include phosphorus from fertilizer, pet excrement and imported compost. Minimizing these small-scale inputs can positively influence phosphorus management.

Increased awareness of phosphorus sustainability could also encourage consumers to develop a recognition of the value of purchasing products that are more sustainable and reuse or reprocess phosphorus. As individual behavior and mindsets shift to buoy improved phosphorus management, this can extend to advocacy for new policies, regulations and company action, pushing organizations, institutions and the government to act more swiftly and urgently. The EU, for example, lists phosphorus on their critical raw materials list based on its economic importance and insecure supply.

At Marquette, you balance this important research work with your role as an engineering educator. How do you connect your research with your mentorship of future STEM leaders?

I think the field of environmental engineering is extraordinarily exciting because of the obvious contributions to protecting human health. This was what originally got me interested in the field. You mean I can actually solve problems that advance human and environmental health protection? Woohoo!

I continue to try to emphasize this connection in all my activities – research as well as teaching and mentoring. New generations of engineers with passion for addressing environmental problems hold tremendous promise for our collective future. To do this, it is important that we continue to attract and retain diverse, talented individuals. For example, as an engineering discipline, environmental engineering has one of the highest percentages of females. Along with my colleagues, I am proud to continue to provide training and mentorship that builds a culture of inclusivity and is attractive and welcoming for all students as we must leverage diverse contributions and skillsets to drive convergent problem-solving teams able to solve some of the world’s greatest challenges.