Impact of dimethyl-, diethyl- and dioctyl- phthalates on rumen ecology.

Phthalic acid esters (PAEs) are produced in large quantities by industry because they are suitable constituents of plastics, thanks to their chemical properties. Considering the great risks for human health due to exposure to PAEs, the problem related to the effects of these plasticizers on food-producing animals should not be put on the back burner because foods represent one of the first pathways of their absorption for humans. Recent studies suggest that phthalate contamination in the rumen can affect its function and alter the microbial balance. Hence, understanding what happens after ingestion is crucial. This study assessed the impact of dimethyl-, diethyl-, and di-n-octyl- phthalate (DMP, DEP, and DOP, respectively) on rumen fermentation and microbial communities, by means of an in vitro approach. Phthalates significantly altered the fatty acid profile. Saturated fatty acids decreased, while monounsaturated and polyunsaturated ones increased under DEP treatment. The DOP reduced C20:4 n-6 and C22:6 n-3. Stearic acid (C18:0) remained dominant but decreased in DEP and DOP conditions. Several C18:1 isomers and omega-3 were affected, particularly by DOP. The highest abatement of phthalates was observed for DOP (63.062%), while DEP and DMP (5.159 and 4.838%) had a similar low decrease compared to the initial concentration. Microbial community analysis revealed shifts in beta diversity, with DEP causing the most distinct changes. Bacterial genera such as Rhodococcus and Streptococcus increased in DEP, while other genera like Aliarcobacter and Parabacteroides declined. DEP, DMP, and DOP induced genus-specific responses, highlighting PAE-selective impact on rumen ecology.