Spatial distribution of microplastics in a large watershed: a case study of the Ottawa River watershed.

River water was sampled at 105 locations in the Ottawa River watershed and analysed for microplastics. Sampling techniques were standardised and replicated at each sample location to give an indication of the spatial extent of microplastics at the watershed scale. Microplastic concentrations remained largely uniform, with no clear accumulation of microplastics towards the lower reaches of the watershed. An ANCOVA analysis determined that the only significant relationships to microplastic concentration were distance downstream on the main channel and tributaries and an increase of microplastic concentrations at boat launch locations. However, these relationships were not strong (R2 value of 0.15) and suggest a more complex interaction of microplastics in large watersheds. It is recommended that further research on microplastic pollution in rivers needs to also focus on temporal factors in addition to considering sinks as an important element in the distribution of microplastics at the watershed scale.

Citizen science sampling programs as a technique for monitoring microplastic pollution: results, lessons learned and recommendations for working with volunteers for monitoring plastic pollution in freshwater ecosystems.

A citizen science microplastic monitoring method was developed to engage the public and quantify microplastic contamination at various sites along an approximately 550 km length of the Ottawa River from Lake Temiskaming to Hawkesbury, Ontario, Canada. The volunteers filtered 100 L of river water through a 100-µm mesh at their desired location along the Ottawa River. All but one of the river samples (n = 43) contained microplastics, with the vast majority of microplastics identified as microfibers. Microplastic concentrations ranged from 0.02 to 0.41 microplastic pieces per litre. We noted numerous advantages in working with citizen scientists including actively engaging citizens in the research, ease of recruiting volunteers within the established Ottawa Riverkeeper network, and expanded spatial coverage at minimal additional costs. Despite these important advantages, there are some important considerations with citizen scientist sampling including the rare events where volunteers mislabelled sample sheets (e.g. labelling as control instead of river sample) and the relatively low volume of water (100 L) that the volunteers could easily sample using our methodology. Recommendations for future citizen science projects for freshwater microplastic research include utilising an established and engaged network, running both field and lab control samples (blanks) to obtain estimates of contamination with microplastic fibres, and increasing the amount of water filtered to obtain more reliable estimates of microplastic pollution in our freshwater ecosystems.