Submitted to: Journal of Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2015
Publication Date: 7/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62737
Citation: Hakk, H., Shelver, W.L., Casey, F.X. 2016. Fate and transport of the ß-adrenergic agonist ractopamine hydrochloride in soil-water systems. Journal of Environmental Science. 45:40-48.
Interpretive Summary: The feed additive ractopamine is registered for use as a leanness-enhancing agent in the US for swine, cattle and turkeys. It is excreted largely as parent compound or metabolites that can readily revert back to ractopamine. Ractopamine has not been evaluated for its movement through agricultural soils following rain or snowmelt. We hypothesized that a portion of fortified ractopamine in soil would remain mobile with water, while the remainder would be immobile through strong binding to soil. If true, this would provide a mechanism for ractopamine to move in the environment to affect non-target animal and plant species. In laboratory soil:water studies we added radioactive ractopamine to soils that differed in biological activity and organic matter, and monitored ractopamine fate over time. Consistent with our hypothesis, most of the ractopamine bound to soil and presumably became biologically inactive. Also consistent with our hypothesis, a smaller portion of the fortified ractopamine remained unbound to soil and was mobile with water. The soil:water studies demonstrated that ractopamine soil movement was governed by the soil’s organic matter content. Our findings suggest that the common practice manure application may help disperse ractopamine in the environment when accompanied by rain/snowmelt events, but that the movement is highly dependent on soil type.
Technical Abstract: The feed additive ractopamine hydrochloride was fortified at four concentrations into batch vials containing soils that differed in both biological activity and organic matter (OM). Sampling of the liquid layer for 14 d demonstrated that ractopamine rapidly dissipated from the liquid layer. Less than 20% of the fortified dose remained in the liquid layer after 4 h, and recoveries of dosed ractopamine ranged from 8 to 18% in the liquid layer at 336 hr. Sorption to soil was the major fate for ractopamine in soil:water systems, i.e., 42-51% of the dose at 14 d. The major portion of the sorbed fraction was comprised of non-extractables; a smaller fraction of the sorbed dose was extracted into water and acetone, portions which would be potentially mobile in the environment. Partitioning coefficients for all soils suggested strong sorption of ractopamine to soil which is governed by hydrophobic interactions and cation exchange complexes within the soil OM. Ractopamine degradation was observed, but to mostly non-polar compounds which had a higher potential than ractopamine to sorb to soil. The formation of volatiles was also suggested. Therefore, despite rapid and extensive soil sorption, these studies indicated a portion of ractopamine, present in manures used to fertilize soils, may be mobile in the environment via water-borne events.