Highlights

• Microplastic (MP) particles are present in archaeological sediment samples.

• MP particles, of 16 polymers, were found in archived and contemporary samples.

• MP levels varied from 0 to 20,588 MP/kg dependant on location and depth.

• MPs may impact scientific value and preservation of archaeological deposits.

Conclusions

This is believed to be the first evidence of MP contamination in archaeological sediment (or soil) samples with polymers and size ranges measured and while accounting for procedural blanks. These results support the phenomenon of transport of MPs within archaeological stratigraphy, and the characterisation of types, shapes and size ranges identified therein. Through contamination, MPs may compromise the scientific value of archaeological deposits, and environmental proxies suspended within significant sediment, and as such represent a new consideration in the dynamism of, as well as arguments for preserving, archaeological deposits in situ.