Colonisation of plastic pellets (nurdles) by E. coli at public bathing beaches

Highlights

• Biofilm colonising marine plastic debris has been termed the ‘Plastisphere’.

• The plastisphere can also be a vector for pathogens and faecal indicator organisms.

• Beach-cast plastic nurdles on public beaches were colonised by E. coli and Vibrio spp.

• Nurdle pollution on beaches could lead to a higher exposure to potential pathogens.

Abstract

The hard surface of waterborne plastic provides an ideal environment for the formation of biofilm by opportunistic microbial colonisers, and could facilitate a novel means of dispersal for microorganisms across coastal and marine environments. Biofilms that colonise the so-called ‘plastisphere’ could also be a reservoir for faecal indicator organisms (FIOs), such as Escherichia coli, or pathogenic bacteria such as species of Vibrio. Therefore, the aim of this study was to map the spatial distribution of beach-cast plastic resin pellets (nurdles) at five public bathing beaches, and quantify their colonisation by E. coli and Vibrio spp. Nurdles were heterogeneously distributed along the high tide mark at all five beaches, and each beach contained nurdles that were colonised by E. coli and Vibrio spp. Knowledge of E. coli colonisation and persistence on nurdles should now be used to inform coastal managers about the additional risks associated with plastic debris.

Introduction

The most abundant form of litter in the marine environment is plastic, which due to its buoyant and persistent characteristics can provide an ideal environment for the formation of biofilm by opportunistic microbial colonisers. The interface between the plastic surface and the environment has been termed the ‘Plastisphere’ (Zettler et al., 2013), and such biofilm formation on marine plastics could provide plastisphere communities with a niche for protection from harmful UV irradiance and predation.

One of the most common types of plastic in the marine environment are virgin plastic resin pellets (or nurdles), a disc shaped plastic particle, typically 3–5 mm diameter, used as the raw material in the production of many thermally moulded plastic products. Nurdles can be accidentally released into the environment, and commonly enter marine systems through ship spills, road runoff, inland waterways, or wind transfer (Boucher and Friot, 2017). Once in the marine environment, nurdles can be deposited in coastal areas via winds, surface currents, and tides (Karkanorachaki et al., 2018), with the potential to be dispersed over long distances (Karlsson et al., 2018). Therefore, nurdles could act as a significant vector for hitchhiking microbes, and facilitate subsequent transport to beaches, bathing waters and shellfish harvesting waters (Keswani et al., 2016).

In Europe, the Bathing Water Directive (BWD), 2006/7/EC, uses faecal indicator organisms (FIOs), such as Escherichia coli, as the key monitoring parameter for regulating compliance of microbial water quality. However, whilst plastic litter in bathing water can influence the survival of E. coli (Quilliam et al., 2014), its ability to bind to, and persist in, the plastisphere of marine plastic debris is currently unknown. Thus, an improved understanding of the potential for nurdles to facilitate the survival of FIOs and human microbial pathogens (e.g. species of Vibrio), and thus increase human exposure routes by providing a vehicle for dispersal around coastal waters, is clearly an area of marine environmental pollution research that needs urgent investigation. Therefore, the aim of this study was to test the hypothesis that nurdles deposited on bathing beaches can act as a vector for E. coli persistence at public bathing beaches.