Potential Water Quality Impacts of Organic Chemicals Used in Feedlot Industry

Abstract:
There are approximately 462 different organic products used by the beef feedlot industry in Alberta. These chemicals include vaccines, anthelmintics and parasiticides, hormones, insecticides, feed medications, antimicrobials and miscellaneous chemicals. My talk will focus on the potential water quality impacts of hormones, antibiotics and insecticides. Hormones may be derived from human and animal waste, or from plants as phytoestrogens. The environmental concern with hormone use is potential effects on crops and possible endocrine disruption in non-target animals. Endocrine disruptors are chemicals that interfere with normal function of hormones and the way hormones control growth, metabolism and body functions. Hormones used in feedlots are applied as ear implants in steers and heifers, or as feed additives in heifers. Hormones increase weight gain, and result in leaner meat and less fat. The main hormones used in feedlots are testosterone, estradial, progesterone, MGA, trenbolone and zeranol. Studies have shown that hormones can be excreted in urine and feces. One study found that 50% of progesterone applied to cows was excreted in the feces and 2% in the urine, and that 12% applied to steers was excreted in feces and 1.2% excreted in urine. Most hormones are fat-soluble compounds and should not be very soluble in water, and would be expected to have a low potential to move in the environment. However, testosterone was found to be rapidly leached from soil, but estradiol and estrone were strongly bound and did not leach. A study in the Chesapeake Bay watershed found that runoff from manured land (poultry manure) may be a source of testosterone and estrogen in streams. Another study found 17 - estradiol in runoff from pasture applied with poultry manure, but found that poultry manure amended with alum reduced runoff losses. Antibiotics are organic substances produced by microbes that have the ability at low concentrations to inhibit growth of, or destroy another microbe. Antibiotics improve growth and feed efficiency, disease prevention and therapy of cattle. The environmental concern is possible alteration of the microbial floral, which could cause disease and development of resistant strains of microbes. Antibiotics used in feedlots include various ionophores, bacitracin, chlortetracycline, erythromycin, oxytetracycline and tylosin. One study found that 75% of dietary chortetracycline was excreted in the manure and urine. They also noted that less organic matter was oxidized in the treated steers, which suggests that antibiotics in the manure may make it less biodegradable. Antibiotics would be expected to have a wide range in water solubilities, and are generally more soluble than hormones. Insecticides are used in feedlots to control parasites. The environmental concern about insecticides is the potential to impair growth and kill non-target organisms in soil and water, and possible carcinogen and endocrine disruptor effects. Most insecticides are used for external control, but ivermectin is used for both external and internal control of parasites. Regardless of the method of application, ivermectin was excreted in the feces. One study on water quality implications of ivermectin use in feedlots found no adverse impact on either surface runoff or subsurface flow. They found it was tightly bound to soil, and degraded to a metabolite that was nontoxic to aquatic organisms. Overall, there were few or no studies on environmental fate of hormones, antibiotics or insecticides used in feedlots. Composting may be a potential management tool to decrease or eliminate these organic chemicals in beef feedlot manure.