Desorption Resistance of Polycyclic Aromatic Hydrocarbons in Biochars Incubated in Cow Ruminal Liquid in Vitro and in Vivo.

Biochar is a new, promising, and sustainable feed additive alternative in agricultural production, which may, however, contain a considerable amount of polycyclic aromatic hydrocarbons (PAHs). As a measure of their bioaccessibility to ruminants, we quantified PAH concentrations in biochars before and after three different incubation experiments. Specifically, the biochars were subjected to (1) an aqueous cyclodextrin suspension with a contaminant trap as (infinite) sink, (2) an in vitro experiment with cow ruminal liquid and a contaminant trap, and (3) an in vivo experiment within cow rumen. Three different biochars were used that contained 13-407 mg/kgdw of the sum of 16 U.S. EPA PAHs before the exposure. While experiment (1) resulted in no or minimal bioaccessibility (desorption resistance) of the PAHs expressed by their largely unaltered concentrations, experiments (2) and (3) caused concentration reductions on average by 35 and 56%, respectively, presumably mainly due to the presence of the ruminal fluid in (2) and (3), and the extended sorption capacity in (3). Thus, simple and "abiotic" passive sampling methods may not capture all processes contributing to bioaccessibility in complex biological systems. A comparison with average daily PAH intake of ruminants suggests that quality-controlled biochar containing <10 mg/kgdw PAHs will not pose an increased risk when applied as a feed additive.