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SRIF's Activities - Agricultural Pharmaceuticals in the Environment

There are over 1800 approved animal drug formulations used in agriculture.  Antibiotics make up a major subset of those drugs.  Of the 23 million kilograms of antibiotics used in the United States annually, over 11 million kilograms are used in agriculture. Most of the agricultural antibiotics are administered in sub-therapeutic doses on a nearly constant basis through their addition to food and water in large-scale animal feedlot operations (AFOs).  Most of the antibiotics administered are excreted in the animals’ waste, often by as much as 100%.  AFOs produce over 118 billion dry kilograms of waste annually.  Runoff and leaching from that waste introduces antibiotics and other chemicals into surface and ground water.  Environmental antibiotics may alter the ecology of watersheds and may produce hazardous strains of antibiotic-resistant bacteria.  Although preliminary studies have documented the presence of antibiotics in surface and ground water, little is known about the full extent of the incidence and transport of environmental antibiotics.  The first step to understanding the environmental impact of antibiotics is to quantify their levels in the watersheds where they are likely to occur.

Antibiotics have been found to be harmful to all levels of the food chain.  Nitrification is an important process in the aquatic environment.  It is a process whereby ammonia is converted to nitrates and then nitrites by the bacteria Nitrosomonas and Nitrobacter.  Oxytetracyline was found to inhibit nitrification potentially causing a toxic build up of ammonia [Klaver, et al., 1994].  Flumequine, a fluorinated quinolone antibiotic, was found to be toxic to the aquatic plant Lythrum salicaria L., where levels as low as 50 mg/L were found to inhibit growth of this submerged aquatic species (Migliore, et al., 2000).  Another study of 8 antibiotics found toxic effects on the blue-green algae Microcystis aeruginosa and the green algae Selenastrum capricornutum at levels as low as 3 mg/L (Halling-Sorensen, 2000).  The toxic effects of 9 antibiotics were tested on the freshwater crustacean Daphnia magna.  Reproductive and toxic effects were noted at concentrations in the low milligram per liter (parts per million) range (Wollenberger, et al., 2000).

Clarithromycin, erythromycin, roxithromycin, chloramphenicol, sulfamethoxazole and trimethoprim have been detected in both sewage treatment plant effluents and nearby surface waters [Hirsch, et al., 1999].  The typical concentrations for these antibiotics found in surface waters were near 1.0 mg per liter (parts per billion, ppb) of sample water. The limits of quantitation used in this study were reported between 20-50 ng/L (parts per trillion).  Residues of sulfonamide and tetracycline antibiotics have been found in surface and ground water at sub-microgram per liter levels [Lindsey, et al., 2001]. 

In the latest study, members of a team from the U.S. Geological Survey’s Toxic Substances Hydrology Program completed the first phase of a National Reconnaissance of Emerging Contaminants.  It included 139 streams in 30 states which were tested for the presence of 23 veterinary and human antibiotics, 12 prescription drugs, 5 non-prescription drugs, 15 steroids and hormones as well as a host of waste-water related organic pollutants [Kolpin, et al., 2002].  Highlights of the antibiotic component of their study included finding erythromycin in 21.5%, lincomycin in 19.2%, sulfamethoxazole in 19.0%, trimethoprim in 27.4% and tylosin in 13.5% of the samples tested.  Maximum concentrations of antibiotics were all in sub-ppb concentrations.

While the toxic levels of antibiotics are generally higher than those levels found in surface and ground water monitoring studies to date, much lower levels can cause problems of their own.  Antibiotic resistance in Acinetobacter spp. has been noted in waters near sewage outflow from hospitals (Guardbassi et al, 1998).  It is not surprising to see that the use of antibiotics in poultry has been shown to produce antibiotic-resistant bacteria in the environment that can be transported to humans.

The central hypothesis of the proposed study is that antibiotics are present in Delmarva Peninsula watersheds, and they originate from agricultural activities.  It is proposed that a study be conducted to (i) quantify antibiotics in surface waters of the Delmarva Peninsula, and (ii) correlate those antibiotic concentrations more closely with either human activities or agricultural practices. 

The main objectives of the proposed study are to increase the utility of existing analytical methods by developing field-portable sample-extraction techniques and improving the sensitivity of instrumental techniques; assemble a suite of common-use antibiotics and other compounds that are indicative of either human and household waste or agricultural runoff; contribute incidence and transport data to the national discussion of environmentally occurring antibiotics; provide a factual basis for the formulation of adequate policy for antibiotic use.

The objectives of this study will be met by taking from six to ten surface-water samples over a one year period from five Chesapeake tributaries on the Delmarva Peninsula.  The sampling sites are currently monitored by US Geological Survey gauging stations which measure water depth and flow.  The ~10 L samples will be filtered for suspended particulates and extracted with solid-phase extraction (SPE) tubes in the field.  The filters and SPEs will then be extracted in the lab and analyzed by high-performance liquid chromatography-mass spectrometry for a suite of representative antibiotics as well as a suite of representative anthropogenic chemical markers. Correlations between antibiotics and chemical markers will be examined to prove or disprove the working hypothesis.

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