Adsorption and Protection of Environmental DNA (eDNA) on Polymer and Silica Surfaces

The interactions of environmental DNA (eDNA) with microplastics (MPs) in aquatic ecosystems are influenced by water chemistry and the surface properties of plastics, impacting the fate of genetic material. While MPs' fate and transport have been studied extensively, the adsorption of eDNA onto polymer surfaces and its persistence remain less understood. Here, we systematically studied eDNA adsorption onto poly(ethylene terephthalate) (PET), polyethylene (PE), and silica (Si) surfaces, where the latter material was used as a proxy for comparison to natural particles. Using quartz-crystal microbalance with dissipation monitoring (QCM-D), the impact of varying ionic conditions that mimic freshwater and seawater environments was analyzed for adsorption rate and extent. The role of cations, particularly divalent ions such as Ca²⁺, in promoting eDNA adsorption through cation bridging was particularly important. PET exhibited the highest adsorption rates, followed by those of PE and Si. Adsorption of eDNA in seawater led to thicker and more rigid adlayers compared with freshwater conditions. However, eDNA adlayers were susceptible to enzymatic degradation and replacement by DNase in both freshwater and seawater, suggesting limited protection from decay. Consequently, the longevity and potential for transfer of material over time and distance are brought into question. This study provides insights into the adsorption mechanisms and stability of eDNA on MPs, advancing our understanding of how MPs influence the transport and persistence of genetic material, including antibiotic-resistant genes, in aquatic environments.