Sand is the most extracted solid material on Earth, but it’s not an infinite resource. Sand mining can damage delicate ecosystems when removal operations trigger erosion and habitat loss, and lax oversight often allows for illegal operations. Without eyes following the raw material from sand mine to Home Depot truck, there’s no way for consumers to verify sustainable sources.
Now, as documented in a new study published in Communications Earth and Environment, scientists have figured out how to trace sand from source to sold.
“Sand mining is the biggest sustainability issue you’ve never heard about. Our entire world is built of sand.”
“Sand mining is the biggest sustainability issue you’ve never heard about,” said Zachary Sickmann, a geoscientist at the University of Texas at Dallas. “Our entire world is built of sand.”
Sickmann was studying how rivers carry sand from mountains to the sea when he realized that the tools he uses to identify specific mountain ranges and rivers that supply sand—tools that measure appearance, texture, and geological makeup—might also work for commercially sold sand.
To test the theory, Sickmann and his colleagues needed to know whether commodity sand retains its fingerprint throughout the industrial process. The researchers collected 41 samples from seven sand sourcing areas in Texas. They sampled sand directly from mine pits, sand stockpiles at concrete plants, and ready-mix concrete from Home Depot—a mixture of powdered Portland cement, sand, and gravel.
They collected both raw and processed sand at each site and measured each sample’s composition and particle sizes to show that sand from each source remained distinguishable at its final stage. “We could see very distinctive pieces with just our eyes. Even as a trained sedimentologist, I wasn’t expecting it to be that obvious,” Sickmann said.
The group realized that if scientists could see the differences, they could train a simple image analysis algorithm to recognize unique sand “fingerprints” as well. They built sandID, an algorithm that was 90% effective at determining the original mining source for surveyed construction site samples. Sickmann said he hopes to expand the tool to a phone app for public use.
Traceability and source assurance have been missing from the sand industry, said Chris Hackney, a fluvial geomorphologist at Newcastle University who was not involved in the study. “I think there’s an appetite for this,” he said.
Meeting Global Sand Demand
Sustainable sand mining often involves digging a deep pit in the ground and cleaning out the soil in a series of complex and costly steps. It’s much cheaper and easier to drive a dump truck onto a beach or riverbank and collect sand to use in concrete and other infrastructure. But that sand is important for keeping waterside environments in equilibrium.
The Texas sand supply chain is relatively simple and transparent, but Sickmann and his colleagues don’t plan to stop there. With the success of this model, the practice of sand sourcing could be expanded to other regional markets. For example, Southeast Asia has a complex network of sand mining regulations, high demand for sand, and diverse geology, so it offers the perfect combination of factors for the new tool to have an impact.
The team plans to help build a database of “fingerprints” so commercial sand can be compared to nearby sources. Fortunately, sand supply networks are relatively simple and are not profitable beyond a certain distance. “These materials are consumed in huge amounts, and they’re also very heavy, very cheap, and very costly to transport. The moment that you increase the transportation distance, the price increases,” said coauthor and sustainability scientist Aurora Torres from the University of Alicante in Spain.
The tool has applications beyond modern compliance tracking. “You could test historical buildings to get an idea of where the materials that were used to build those structures came from and which areas were mined and targeted for producing materials,” Torres said.
As urban centers rapidly expand and sand demand skyrockets, it is important to keep in mind all the potential impacts of unsustainable sourcing. “When we think about sand sustainability, it’s all about scarcity,” Torres said. “But we shouldn’t also forget that the human and the environmental dimension is equally important.”
—Molly Herring (@mollymherring), Science Writer
4 January 2024: This article has been updated to correct Chris Hackney’s affiliation.