JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. Ira Flatow is away. Later this hour, we’ll take a trip back to a classic interview with Jane Goodall, and we’ll put some cicadas on your menu.

But first, you’ve heard the expression, “As numerous as the stars in the sky or the grains of sand on the seashore.” But sand isn’t actually in unlimited supply across the globe, and our demand for it keeps growing, for everything from the sidewalks under your feet to the glass screen on your phone. There’s no danger of planet Earth running out of sand, of course, but the economics and the ecological impacts of the sand industry are shifting. Joining me now to talk about the ecology of sand is Dr. Aurora Torres. She’s a postdoc in the Center for Systems Integration and Sustainability at Michigan State University and at the Catholic University of Louvain in Belgium. Welcome to Science Friday.

AURORA TORRES: Thank you for having me.

JOHN DANKOSKY: Let’s get a definition first. What do we mean when we say “sand”? What is it?

AURORA TORRES: It’s simply a matter of size. Sand is defined by a specific grain size. So from 16 to 1 to 2 millimeters is just very fine grains that define what sand is. But actually, the composition or the shape can differ. And it can be made from natural materials, from fragments of rocks and minerals, but it can be also made by crushing plastics or recycled concrete and mortar.

JOHN DANKOSKY: Not all sand is the same. And I think that we all have this experience– if we walk on a beach on the Mediterranean, or we walk on the beach in the Northeast, the sand under our feet is a little different. Is there good and bad sand for different types of uses?

AURORA TORRES: Yeah, so it depends on, what is the final use of sand? For many different types of applications, we don’t have to be very strict about the quality of the sand. But for certain things, like producing glass or for the microprocessors that power our cell phones, then we need a very high quality of sand that is quartz sand, almost basically 100% of quartz.

JOHN DANKOSKY: If we’re going to make sidewalks or we’re going to make a building out of concrete, what type of sand do you want? Where do you want that sand to come from?

AURORA TORRES: It can be from a multitude of places. Many people think that the ideal type of sand comes from river, but actually, we can make crushed rock that can be of similar or even higher quality than the sand that we find in the river, because we have better control over the sizes of the grains, the distribution of the grains in the sample, the shape– we can make angular sand or more round sand depending on the use. So mainly speaking, that type of sand that we use for concrete is coming from rivers, flood plains, glacial deposits, and crushed rock.

JOHN DANKOSKY: Let’s say you take sand from the Sahara Desert. Is that something that you can build a building out of?

AURORA TORRES: It’s not the ideal type. It will require a lot of processing to be able to use desert sand. Many teams are looking for opportunities to do that [INAUDIBLE] for the places that are next to the deserts, of course. But in principle, it’s difficult, because the grains of sand have been eroded by the action of the wind, and they are very round. And also, if you look through the microscope, it’s like all the grains of sand look the same, while ideally, what we would expect to find for a good mix of sand to make concrete, is a diversity of grain sizes, with different shapes and slightly different sizes. And we don’t find that in desert sand, so that’s why this is not an ideal type of source.

JOHN DANKOSKY: So you’re saying that sand that’s uniform in size and shape doesn’t make good construction materials, but sand that’s diverse in its size and its different qualities, that makes better construction material. Why is that?

AURORA TORRES: If the grains are very round, then the mix is not strong enough, and the concrete kind of collapse. So for the mix to stay together, you need these angular grains of sand. But it also gets complicated because if it’s too angular, then it might not be that good. So it has to be within a certain range.

JOHN DANKOSKY: Do we know how much sand is on the planet?

AURORA TORRES: No, we don’t know. That’s still a question that is yet to be answered. There is no geological assessment of deposits and their uncertainty that has been conducted. So we don’t know.

We think is very abundant. In general, geologically speaking, it’s widely distributed on land, on freshwater systems, in coastal areas. But we don’t know how much sand there is and how much sand of different qualities is on the planet.

JOHN DANKOSKY: So when we say that there’s a sand crisis, I mean, there’s no real chance of running out, because we do have a lot of sand. So what are we talking about around a crisis of sand?

AURORA TORRES: So it’s mainly our relationship with sand what is changing. Sand is a material that has been used for construction for a very long time. The Egyptians started to make a type of concrete. The Romans perfectioned the technique.

But it has been since the ’50s, 70 years ago, that with population growth, urban development, and infrastructure development, the extraction of sand and gravel has accelerated to the point that these are now the most extracted materials in the world beyond fossil fuels and biomass. We extract 50 billion tons of sand and gravel every year. And then, this is bringing environmental and socioeconomic implications. So that’s why we talk about a global sand crisis.

JOHN DANKOSKY: Demand for oil may be slowing down because we’re finding other ways to power ourselves. Are there alternatives to sand that people are looking at in order to stop this looming crisis?

AURORA TORRES: Yeah, that’s very interesting, because making this comparison as we are transitioning now from gas and fuels to renewable energies, not because we completely run out of these materials, but because of the environmental implications, we are trying to find secondary resources that can replace sand and gravel found in river systems that are highly vulnerable. And the main source to get the sand and gravel is crushed rock. And this is already the main source of aggregates in places like the United States or in Europe. And we are seeing an increasing adoption of this type of production that is basically come from blasting and crushing rocks of different types– granite, sandstone, basalt. A wide diversity of rocks can be used for that purpose.

And we also see a widening range of secondary resources that can be used to satisfy the demand for aggregates. The main one is recycled construction and demolition waste. But in the future, there will be probably increased adoption of recycled plastic, byproducts of steel production, byproducts of other mining industries. So there is potential for reducing the demand for primary materials.

JOHN DANKOSKY: You mentioned that sand is so in demand around the globe and it’s so heavily extracted, we made the comparison to the oil industry. Are we seeing wars over sand the same way that we have seen wars over oil?

AURORA TORRES: Well, it has certainly become an issue that has created geopolitical conflicts. One of the clearest ones is in Singapore, that has been growing by 23% in the last decades because of massive land reclamation projects for urban development. And this has created conflicts with the countries in Southeast Asia nearby Singapore, because Singapore just doesn’t have enough materials for all this construction that is going on. So it has to rely to a certain percentage on importing these materials from neighbor countries, from Vietnam, Indonesia, Malaysia.

Singapore was accused of stealing sand from islands in Indonesia, and a total of 23 islands disappeared in a very short period of time. And after that, Indonesia accused Singapore of this illegal extraction. And there has been a succession of exporting bans to Singapore because of accusations of environmental impacts associated with this extraction.

And also, within countries, we have seen that as sand mining has become increasingly profitable, and when there is not a strong governance in place, many illicit supply networks have emerged. And one of the best examples is in India, where there are multiple operating Indian sand mafias taking control of these reserves and threatening local communities and also being blamed of murdering hundreds of people in the last years in sand wars.

JOHN DANKOSKY: That’s extraordinary. Sand mafias.

AURORA TORRES: Mm-hmm. It’s really surprising, and it’s not only in India that happens, but also in China, in Kenya. In Baja California, there are problems, also, of illegal mining. And so it’s quite an extended problem when there is weak governance and a very high demand.

JOHN DANKOSKY: What do you think we can do to make sand more sustainable?

AURORA TORRES: I think we need a more careful monitoring and planning of the resources that we have. We need a better understanding of the physical system. So to put it in simple terms, to know what the geological resources are and to understand the extraction flows and how they accumulate on urban areas, because in the future, it might be secondary resources. And in this physical system, we should also get an understanding of the secondary resources that are available in a given place that we might be able to access in order to promote a transition towards a more circular economy that increases the efficiency in the use of the materials and reduces the reliance on the primary materials.

But there is also a bit of an uncomfortable truth that was highlighted by a report of the international research panel last year. In this report, they concluded that material efficiency strategies in the construction sector can achieve big gains in terms of reducing climate change emissions, but the ones that are going to be really more influential are the ones that require a societal transformation, so moving into more lifestyles that require less material. And interestingly, that goes against the tide of ongoing urban sprawl and increasing floor area per capita that is expected to double in the next year. So unless we couple efforts in technical measures with social measures, we might be eating up what we gain by increasing material efficiency. So yeah, that’s something we need to find out– how to make that societal transition towards decreasing the material demand per capita.

JOHN DANKOSKY: Dr. Aurora Torres is a postdoc in the Center for Systems Integration and Sustainability at Michigan State University and at the Catholic University of Louvain. Thank you so much for joining me today. I really appreciate it.

AURORA TORRES: My pleasure. Thank you so much.

Copyright © 2021 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/