Antibiotics in the Environment
Antibiotics have recently been detected in surface water bodies around the country.
Low levels of antibiotics have recently been detected in surface water bodies around the country (Kolpin et al., 2002). In Colorado in particular, Yang and Carlson (2003) have reported tetracycline and sulfonamide levels in the Poudre River and have concluded that there are both urban and agricultural influences on the occurrence of antibiotics in the river.
There are several potential sources of antibiotics including human and animal uses that could be transmitted to a water body through wastewater treatment plants, feed mills, lagoons, or runoff from livestock operations or manured fields. Ken Carlson’s group at Colorado State University recently sampled seven dairy lagoons and seven dairy manure stockpiles and analyzed them for several antibiotic classes. The lagoon samples ranged from non-detectable (ND) levels to 17 parts per billion tetracyclines, ND to 17 parts per billion sulfonamides, and 19 parts per billion for the macrolides. The solid manure samples also ranged from non-detectable levels to 5130 parts per billion tetracyclines, ND to 46 parts per billion of sulfonamides, and ND to 5 parts per billion macrolides.
Antibiotics have been found in water bodies and in manure sources, but the question remains: are antibiotics transported from livestock manure and wastewater storage areas to water bodies? We have begun transport studies to evaluate runoff and leaching of antibiotics from manured fields, but many unanswered questions remain. Carlson’s most recent work documents monensin in the agricultural areas of the Poudre River. This is particularly important because monensin has no human use; therefore, it serves as a marker illustrating that the cattle industry is a source of antibiotic contamination in this water body.
In addition to identifying contamination sources, we need to know whether the levels measured in water bodies are high enough to have negative environmental impacts. In general, most measured concentrations have been well below (an order of magnitude lower) the levels that have been shown to be toxic to standard testing organisms (Boxall et al., 2003). There are exceptions to this general observation including ivermectin and doramectin in manure and monensin in soil (Boxall et al., 2003). Degradation products and interactions among compounds have not been adequately evaluated and could result in synergistic toxic effects.
In addition to direct toxicity effects, antibiotics in the environment could lead to the development of antibiotic resistance, a critical concern as it relates to the efficacy of antibiotics in the treatment of human disease. This is not a new concern; in 1989, the National Academy of Sciences concluded that the use of antibiotics in animal feeding operations was seriously undermining the ability of antibiotics to protect human health. The World Health Organization called for a ban on routine feeding of antibiotics to livestock in 1997. Amy Pruden’s research group at Colorado State University is evaluating the presence of antibiotic resistance genes in the sediments of the Poudre River in order to address this concern.
Other impacts that have not yet been fully evaluated include potential effects on soil fauna (such as earthworms) and microbial populations and processes. Preliminary data show that antibiotics may inhibit the mineralization of manure nutrients in soil (Boxall et al., 2003). There are also potential (but unknown) impacts on crop growth, yields, and quality.
If livestock operations are indeed a source of antibiotic contamination of water bodies, then it will be important to know what manure management decisions can be made to hasten the degradation of antibiotics and limit their potential negative impacts. We are currently evaluating treatments such as composting (Amy Pruden), lagoon aeration (Ken Carlson), and phytoremediation (James Linden) at CSU in order to be prepared to give producers solid recommendations about management options to limit the spread of antibiotics in the environment.
Antibiotics used non-therapeutically in livestock production have been found in surface water bodies. What are the sources of contamination? Are the concentrations high enough to cause harm to humans or ecosystems? If the sources include livestock operations, what can be done to prevent further contamination? These are all questions whose answers are being sought out through CSU’s research programs so that livestock producers can make sound decisions regarding their use and management of antibiotics in the future.
References
Boxall, A.B.A.; et al. Environ. Sci. Technol. 2003, 37, 287-294.
Kolpin, D.W.; et al. Environ. Sci. Technol. 2002, 36, 1202-1211.
Yang, S. and K. Carlson. Water Research 2003, 37, 4645-4656.
