Drinking plastic: a study of microplastic concentrations in drinking water from rural and urban sources in Mali, Africa

Drinking water (DW) is a necessity for life, and its pollution is of global concern for public health. Whilst the global occurrence of microplastic (MP) pollution in various environmental matrices is a focal point for research, the focus on microplastics in drinking water sources is somewhat less. Previous research has shown orders of magnitude difference in MP contamination of drinking water in residential areas, owing to local water source, water contamination, and container material.

Here we explore the exposure of residents living in rural and urban areas of Mali in Africa to microplastics in drinking water from varying sources. DW samples were taken from 83 homes, from urban residents in the city of Bamako and those in several rural settlements to the east of Bamako. These homes received their drinking water from traditional open wells, boreholes (narrower and deeper canals, often newer sources) and taps. Urban areas often had taps in each home, whereas rural areas had communal well and borehole water points.

A litre of DW was collected from each source which was subsequently sieved at 63 um and then washed with deionised water into a 20ml vial before shipping to the UK. Wet hydroxide digestion was carried out using 30% hydrogen peroxide at a minimum ratio of 1:1 sample to peroxide. After 24 hours the sample was filtered, and 80% of samples were mixed for 1 hour with Nile red, concentration 5 ug/ml, followed by filtering on glass fibre disk. These samples were assessed with fluorescence microscopy to assess polymer number and morphology. The remaining 20% were directly filtered onto Anodisc and assessed for polymer number and type using confocal Raman spectroscopy.

Our results capture a range of polymer types, morphological properties, and concentrations in the studied water samples. A statistically significant mean value of 9.9 mp/l (range 1-34 mp/l) for urban DW compared to 6.5 mp/l (range 0-15 mp/l) for rural DW was found. A range in distribution of MP concentration was found across the study sites regardless of geographic assignment. Morphologically fibres were most identified, 69% for rural and 72% for urban. The primary polymer types found were PMMA, PE, PS, PA/nylon, and PET.

The study sets the basis for a wider investigation of water sources in the region, followed by the perspective linking of health outcomes to the MP exposures found.