We studied how the use of animal waste as fertilizer on agricultural lands might influence the health of surrounding water bodies in the Chesapeake Bay. We analyzed rainwater runoff and receiving waters for the presence of antimicrobial-resistant bacteria and pharmaceuticals associated with animal waste fertilizer and detected both in varying concentrations. These efforts will help agricultural communities make land use decisions and plans that reflect their interests and goals for the bay.
Why We Care
Poultry farming in Maryland represents a large and important industry, earning over $790 million in revenue in 2008. The buildup of feces and bedding material on the floor of poultry growing houses is called poultry litter. On the Delmarva Peninsula, application of poultry litter to agricultural fields provides nutrients to the soil and a convenient disposal method. Along with the nutrients come the fecal bacteria and excretion products from the birds. Litter can be a source of steroids and other pharmaceutically active chemicals. Many poultry houses have historically used antibiotics as growth promoters, and fecal bacteria associated with the litter can be resistant to antibiotics. The introduction of antibiotic chemicals and antibiotic resistant bacteria to natural waters next to or near farmland can occur, with poorly understood consequences.
What We Found
We found several pharmaceuticals—including tetracycline, chlortetracycline, and sulfadimethoxine—in some litter samples being applied to agricultural land. We detected antibiotic resistance in fecal bacteria from these sources, but the patterns and levels of resistance varied among samples. Field-applied biosolids contained more varieties of antimicrobials and greater concentrations than did poultry litter. Bacteria isolated from biosolids were more likely to have multi-drug resistance, although there was wide variability in resistance among bacteria.
What We Did
We collected samples of fertilizer, soil, and water and measured the levels of steroids, antimicrobials, and bacteria in the samples. We assessed bacteria for antimicrobial resistance. Our project helped farming communities and water managers better understand if there were any unintended consequences of applying animal waste as fertilizer to farm fields. They could begin to ask questions such as, “How much, if any, will this practice contribute to the bacterial levels in receiving waters? Do antimicrobials persist in the animal waste? Are the bacteria present resistant to antimicrobials?”
Next Steps
We will determine if the levels of pharmaceuticals and antimicrobial resistance in waters near agricultural fields differ from what we might find in surface waters elsewhere in the Chesapeake Bay.