Abstract
With increasing evidence of ingestion and uptake of microplastics (MPs) and nanoplastics by humans, combined with potential toxicological impacts from exposure and accumulation, it is important to understand their primary exposure routes. The ingestion of MPs via consumption of MP-contaminated foodstuffs appears to be an important exposure route for humans. The current study investigated MP levels in commercially available processed white and brown sugars, attempted to identify the primary sources of MP contamination and estimated human exposure to MPs from sugar consumption. The abundance of MPs varied from 18 to 34 items/100 g (270 ± 82 items/kg) in white sugar and from 4 to 20 items/100 g (103 ± 85 items/kg) in brown sugar. The most common MP type was <1 mm in size, black in colour and fibre-like in morphology. The MPs were comprised of PP, PET, CP and PEU, with PP and PET being the most abundant polymers observed in both white and brown sugars. Physicochemical characterisation of the MPs found in the sugar samples suggests that processing steps, and not uptake from soil by sugarcane plants or contamination from plastic packaging, are the main source of MP contamination. Energy-dispersive X-ray spectroscopy (EDAX) revealed a range of elements present on the MP surfaces, some of which are known to be toxic. These might have been derived from metal-based plastic additives or adsorbed from the surrounding environment. Using the available sugar intake data, we estimated that the annual intake of MPs by an average person is approximately 11,262 items/kg-bw/year for white sugar and 10,204 items/kg-bw/year for brown sugar. These MP ingestion levels are at least an order of magnitude higher than for salt and other foodstuffs. The results of this study can serve as a useful basis for implementing mitigation actions to reduce MP contamination during refined sugar production.