Microplastic Contamination Discovered in Archaeological Sediments

Researchers have detected microplastic particles contaminating archaeological sediment samples from excavations in the city of York, UK [1]. The findings, believed to be the first evidence of microplastic contamination in archaeological soils, raise important questions about the long-term preservation of archaeological remains and the impacts of modern pollution on our cultural heritage.

What are Microplastics?

Microplastics are tiny plastic particles, generally defined as being between 1 μm and 5 mm in size. In recent years, microplastics have been found to be ubiquitous in the environment, contaminating marine ecosystems, freshwater, soils, and even the air we breathe. They originate from the breakdown of larger plastic items as well as from microbeads and fibers from clothing, cosmetics and industrial processes.

While the full impacts of microplastics on environmental and human health are still being investigated, studies have shown they can alter soil properties and chemistry, impact soil-dwelling organisms, and potentially enter the food chain. Now, this new research reveals microplastics are also infiltrating archaeological deposits, where their long-term effects remain unknown.

Analyzing Archaeological Sediments

The study, led by researchers from the University of Hull and University of York, analyzed sediment samples from two archaeological sites in central York - Queen's Hotel and Wellington Row. The sites, originally excavated in the late 1980s, contained well-preserved archaeological deposits dating back to the Roman period.

Using μFTIR spectroscopy, the team characterized the number, size and types of microplastic particles present in the archived samples. For comparison, they also took new sediment cores from the same locations in 2023.

In total, 66 microplastic particles comprising 16 different polymer types were identified across the samples. While no significant differences were found between sites, the archived sediments from the 1980s actually contained a greater diversity of microplastic types compared to the contemporary samples.

The most abundant polymers detected included polytetrafluoroethylene (PTFE), commonly known as Teflon, polybutylene sulfone (PSU), used in high temperature applications, and polyethylene (PE) and polypropylene (PP), found in packaging and plastic containers. Most took the form of fragments, likely broken down from larger plastic items.

Importantly, the researchers ran extensive controls to rule out contamination from the sampling equipment, storage containers, or the surrounding environment. This confirmed the microplastics were indeed infiltrating the archaeological layers themselves, to depths of over 7 meters, rather than being introduced during excavation or storage.

Implications for Archaeology and Heritage

So what does this mean for archaeological sites and the information they contain about our past? The short answer is, we don't fully know yet. This is uncharted territory. But there are reasons to be concerned.

Firstly, microplastics could potentially compromise the long-term preservation of delicate archaeological remains, especially organic materials like wood, leather, textiles and ancient DNA that are so well-preserved in waterlogged conditions like those in York. Over time, plastic-associated chemicals and additives could leach into the surrounding soil, altering its chemistry. Microplastic surfaces may also support novel microbial communities whose impacts on archaeological preservation are unknown.

Secondly, the presence of microplastics could interfere with the information we can retrieve from archaeological soils. Sediment-derived artifacts and preserved biomolecules are crucial records of past environments, ecologies and human activities. Contamination with microplastics may confound future analyses, like radiocarbon dating or residue studies. Soils are also records of site formation processes and past landscape changes - how will we distinguish natural soil components from artificial microplastic contamination?

More broadly, this research demonstrates that even our "sealed" archaeological sites are not immune to modern pollution. While the sources of the microplastics at these particular sites in York remain uncertain, it's likely that a combination of floodwaters, groundwater movement, and percolation from above are responsible for introducing both contemporary and historical microplastic contamination into the soil profile.

An Emerging Field

As disturbing as these initial findings are, in many ways this study represents an exciting frontier for both archaeological and environmental research. The interaction of microplastics with the buried archaeological record is a brand new field of study that will require close collaboration between archaeologists, environmental scientists, and materials specialists.

Further research at other sites, in different countries and environments, will help build a clearer picture of the scale and variability of the problem. Detailed analysis of microplastic composition and associated chemicals in different soil types and conditions will clarify the risk they pose to archaeological preservation. Crucially, this work will also help us understand the long-term fate and impacts of microplastics in the terrestrial environment - key questions as we grapple with the reality of plastic pollution worldwide.

Prioritizing Protection

Policies around the protection of archaeological heritage currently prioritize preservation in situ - leaving as much as possible undisturbed for the benefit of future research and public appreciation. The York study suggests we may need to reassess this, as microplastic pollution could mean leaving contaminated remains in the ground is no longer the best way to protect them or their information content for the future.

At the very least, this research highlights the need for even greater care and more extensive sampling during any future excavations at high-risk sites. Detailed microplastic contamination assessments may need to become a routine part of archaeological evaluations.

We may need to consider prioritizing full excavation and meticulous recording, including microplastic analyses, of particularly significant but vulnerable deposits before contamination and loss of information progresses further. Selective sampling and storage of sediments specifically for microplastics research should also be considered.

Collaboration and Public Engagement

Tackling the issue of microplastic contamination at heritage sites will require archaeologists to work closely with site owners, policymakers, and the commercial construction sector to implement workable assessment and protection strategies.

Public opinion will also play a key role. This discovery is yet another reason to care about plastic pollution, and a way to communicate the far-reaching consequences of our modern disposable culture. The idea that our trash is infiltrating and potentially damaging irreplaceable archaeological remains certainly brings home the importance of reducing plastic waste.

The York study is likely just the tip of the iceberg when it comes to microplastic pollution at archaeological sites. While it focused on a historic city with its complex layering of ancient and modern remains, microplastics are being detected in all kinds of soils worldwide, including agricultural land and seemingly remote mountaintops and islands.

As such, it's likely that many other types of heritage sites are being impacted as well - from rural settlements and cemeteries to ancient industrial areas and battlefields. Coastal sites and those near rivers may be particularly vulnerable, but few buried archaeological remains are likely to be completely immune.

The next steps will be to expand microplastic surveys to other locations and site types, prioritizing those most at risk from flooding, development pressure, or already showing signs of degradation. Urgency is key, as plastic continues to accumulate in the environment every day.

At the same time, we need more experimental studies on how different microplastics interact with archaeological materials and soils over time. This will help us predict where they pose the greatest risk and tailor our conservation strategies accordingly.

Lessons From the Past

While the discovery of archaeological microplastics is undoubtedly troubling, it also offers a unique long-term perspective on the enduring impact of our material choices. In the decades and centuries to come, the plastic fragments in these ancient sites will bear witness to our Age of Plastic, long after today's landfills are closed and the last plastic bag is discarded.

Perhaps the realization that our plastic waste is infiltrating our human story at its very roots will be the wake-up call needed to tackle this pollution crisis head-on. In archaeology, as in life, taking responsibility for our trash and the legacies we leave is everyone's concern. Our past, present and future are all inextricably linked - and each contains lessons for the others, if only we're open to listening.