Absorption, distribution, and elimination of [14C] polyethylene terephthalate nanoplastics in lactating sheep upon oral administration

Polyethylene terephthalate (PET) microplastics/nanoplastics (MP/NP) are an emerging contaminant that is often found in the environment and food. The aim of this study was to determine the absorption, distribution, and excretion of PET NP in ewes. Lactating sheep (n = 6) were orally administered a single dose of 2.67 ± 0.19 mg/kg body weight (bw) [¹⁴C] PET NP (230-510 nm, 980 μCi). Three sheep were sacrificed at 24- or 72-h post dosing and radioactivity in feces, milk, urine, and tissues was measured by liquid scintillation counting. Plasma contained low but quantifiable [¹⁴C] PET NP from 2 h post dosing until slaughter and had a long elimination half-life of ~80 h. Total radioactivity recoveries in milk and urine were < 0.02 % and < 0.3 %, respectively. Radioactivity was present in the mammary gland tissue (< 0.01 % recovery) of sheep at 24-h withdrawal, but not at 72-h withdrawal. Quantifiable [¹⁴C] activities were present in abomasum, cecum, colon, omasum, and rumen in animals harvested 24 h post dosing (< 0.7 % recovery, cumulative) but greatly decreased or not detectable at 72 h. [¹⁴C] PET NP residues were not quantifiable in skeletal muscle, liver, lung, or kidney. The majority of the [¹⁴C] activity was detected in feces (~ 75 % at 24-h withdrawal and ~ 99 % at 72-h withdrawal). These data suggest that most dietary [¹⁴C] PET NP would recirculate in the environment through fecal excretion.