Microplastic prevalence in commercially available pet foods

Plastic production has risen dramatically since the 1950s. While microplastic contamination of human food has been investigated, commercially available pet and wildlife foods have not. This could represent a contamination route for terrestrial ecosystems, via the faeces of pets and wild animals. We assessed 38 pet and hedgehog food products available in the U.K., covering a range of brands, price-brackets, and food types. Six 1 g replicates of dried material were tested per product, giving a total sample size of 228. Microplastics were found in 63 samples (27.6%). Of the 38 products, 76% were positive: 29% had one positive sample, and 47% had 2 or more. Most (84%) of the 19 brands tested were contaminated, with value products having more positive samples than mid-range and premium products. The most common polymers were polyester, polyacrylamide, polyethylene, and polypropylene. The mean concentration of microplastics was 0.4 pieces g-1 (SD = 0.84) for all the dry foods tested and 0.3 g-1 (SD = 0.62) in wet foods. Within samples that were plastic-positive, the concentrations were 1.6 pieces g-1 (SD = 0.73) and 1.2 piecesg-1 (SD = 0.53). Given their lower energy content, and correspondingly larger mass consumed, wet foods present the greatest exposure risk. Based on the mean microplastic content across all samples, a large dog (35 kg) fed wet foods is likely to ingest 313 microplastics day-1 (SD = 263.6). Microplastic concentrations in pet food were higher than those reported for human foods but lower than in wild invertebrates. However, pet foods had a greater proportion of positive samples, suggesting they may be an important contamination route for pets, wild mammals and terrestrial ecosystems. This study, therefore, reveals a previously unrecognised pathway for microplastics to enter the food chains of both pets and wild mammals.