Bovine milk and microplastics: Revealing the invisible with advanced microscopy

Abstract

This study assessed the presence of microplastics (MP) in bovine milk marketed in Ecuador, considering milk type, packaging material, and the analytical methodology employed. A total of 35 samples of raw, whole, and semi-skimmed milk packaged in Tetra Pak, plastic pouches, or sold unpackaged were analyzed. Samples were subjected to direct observation (DO), density separation with supersaturated saline solution (SSS), filtration (FSSS), and chemical digestion with 10% NaOH (CD). Raw, unpackaged milk exhibited the highest MP concentrations (241.05 ± 66.18 MP L⁻¹), significantly exceeding those found in semi-skimmed (115.14 ± 24.21 MP L⁻¹) and whole milk (65.83 ± 14.19 MP L⁻¹), suggesting that industrial processing may partially reduce contamination. Unpackaged milk also showed higher MP levels compared to milk in Tetra Pak (92.38 ± 20.56 MP L⁻¹) and plastic pouches (88.60 ± 19.66 MP L⁻¹), indicating a protective effect of packaging. Among analytical methods, DO yielded the highest apparent MP concentrations (390.86 ± 48.48 MP L⁻¹), while SSS, SSSF, and CD reported lower values. CD, corroborated by scanning electron microscopy (SEM), was found to be the most sensitive and reliable technique due to reduced interference. In conclusion, raw and unpackaged milk contained significantly higher levels of MPs, potentially due to factors such as contaminated feed and deteriorated milking equipment. These findings highlight the need to reinforce sanitary control during production, improve processing and packaging practices, and standardize analytical methodologies to ensure dairy safety and protect public health.