Effect of the veterinary ionophore monensin on the structure and activity of a tropical soil bacterial community

Abstract

Monensin (MON) is a coccidiostat used as a growth promoter that can reach the environment through fertilization with manure from farm animals. To verify whether field-relevant concentrations of this drug negatively influence the structure and activity of tropical soil bacteria, plate counts, CO₂ efflux measurements, phospholipid fatty acids (PLFA) and community-level physiological profiling (CLPP) profiles were obtained for soil microcosms exposed to 1 or 10?mg kg^?1 of MON across 11?days. Although 53% (1?mg kg^?1) to 40% (10?mg kg^?1) of the MON concentrations added to the microcosms dissipated within 5?days, a subtle concentration-dependent decrease in the number of culturable bacteria (<1 log CFU g^?1), reduced (?20 to ?30%) or exacerbated (+25%) soil CO₂ effluxes, a marked shift of non-bacterial fatty acids, and altered respiration of amines (1.22-fold decrease) and polymers (1.70-fold increase) were noted in some of the treatments. These results suggest that MON quickly killed some microorganisms and that the surviving populations were selected and metabolically stimulated. Consequently, MON should be monitored in agronomic and environmental systems as part of One Health efforts.     

Effect of feedlot design and management on the fate and distribution of monensin

Feedlots produce a range of trace chemicals that impact human health and/or the environment. The most widely used growth promoter in intensive cattle production in Argentina is monensin, an ionophore polyether with antibacterial and coccidiostatic activity. Several beef cattle feedlots with different management systems, weather conditions, feed types and feedbunk types were selected in different agro-ecological areas of Argentina. Monensin concentrations in samples of pen soil, manure, feed and runoff were analysed. The monensin concentrations measured in soil samples suggest a strong dependence on the type of feed employed in the facility. During feed distribution by trucks to the feedbunks, some feed can reach the soil, thereby increasing the soil monensin concentration close to the feedbunks. The wide range of monensin concentrations detected in manure samples could be explained by the rapid degradation of monensin in the manure matrix. Monensin levels in runoff samples indicated that the distribution of monensin in the environment could be governed by surface phenomena including horizontal movement and adsorption of monensin in particulate material present in the runoff layers. This is the first study of monensin distribution in Argentinian feedlots and serves as the starting point for more sustainable and environmentally friendly feedlot management.     

Preliminary studies on occurrence of monensin antibiotic in Bosque River Watershed

Water quality impact due to excessive nutrients has been extensively studied. In recent years, however, micro-pollutants such as pharmaceuticals and hormonal products used in animal agriculture have added an additional impact to overall water quality. Pharmaceuticals used in the poultry, swine, beef, and dairy industries have been detected in various environmental matrices such as, soil, groundwater and surface water. In this study, 26 surface water samples were collected throughout the Bosque River Watershed (BRW) with samples representing a range of land use conditions and locations of major dairy operations. Samples were analyzed using commercially available Enzyme-Linked Immunosorbent Assay test. Of the 26 samples, three samples consistently tested positive for monensin antibiotic with concentration ranging from 0.30 to 3.41 μg/L. These three samples were collected from sites that received varying amount of agriculture wastes (11.7% to 31.3%) and located downstream from sites associated with moderate levels of animal agriculture. The preliminary results suggest that there is a potential for monensin occurrence in the BRW, although initial findings indicate only very low levels.