Livestock manure can be a valuable source of nutrients and organic matter. On the other hand, manure is also a potential environmental hazard. Nutrient loss from manure can lead to water pollution and eutrophication of lakes and ponds. Bacteria from manure can contaminate water. Human deaths have been attributed to vegetables grown on land where raw manure is applied or salad greens are irrigated with contaminated water. Now there’s another hazard — livestock manure from non-organic farms contains antibiotic residue and antibiotic-resistance bacteria. Scientists speculate that the use of raw manure on fields may contribute to the spread of antibiotic resistance in bacteria (including strains implicated in human disease).
Wallace et al (2018) found that the latest technology used to treat manure slurry from dairy farms was ineffective at eliminating antibiotic residues. After slurry was treated using a full-scale advanced anaerobic digester, the end product contained significant levels of residual antibiotics and the molecules from antibiotics. This material is being sold as fertilizer.
The good news is that the authors suggest a solution. They cite other studies that show antibiotic residue can be substantially reduced by the process of composting the solid waste.
In a related study, Gou et al (2018) examined antibiotic-resistant genes. They found the genes were in cattle manure and also in the soil on fields treated with the manure. Again, there is a silver lining. Gou et al (2018) state that their “results provide evidence that aerobic composting of cattle manure may be an effective approach to mitigate the risk of antibiotic resistance propagation associated with land application of organic wastes.”
Sources: Aerobic composting reduces antibiotic resistance genes in cattle manure and the resistome dissemination in agricultural soils. Min Gou, Hang-Wei Hu, Yu-Jing Zhang, et al. Science of the Total Environment. January 2018, Volume 612, 15 Pages 1300-1310.
Occurrence and transformation of veterinary antibiotics and antibiotic resistance genes in dairy manure treated by advanced anaerobic digestion and conventional treatment methods. Joshua S. Wallace, Emily Garner, Amy Pruden and Diana S. Aga. Environmental Pollution. May 2018, Volume 236, Pages 764-772.
- Janet Wallace