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The objective of this study was to determine whether fish collected from the La Miel or Nechí Rivers (Colombia) differed in muscle methyl mercury (meHg) concentration. Two fish from six different species were collected from markets adjacent to each river. Overall, fish collected from the market adjacent to the Nechí River contained higher levels of meHg. This result however is being driven by very high meHg concentrations in four individual fish, three of which are Pimelodid, long-whiskered catfish. These catfish may represent ideal sentinel organism for the detection of meHg contamination in Colombian rivers.

Analytical methods to improve the detection of erythromycin in water and sediment were developed to optimize for erythromycin's recovery of extractable and bound residues from the aquatic environment. Comparison of solid phase extraction (SPE) and sediment extraction methods were analyzed to determine optimal recovery of erythromycin from water and sediment. SPE methods examined included previously reported methods for macrolide and sulfonamide antibiotics with recoveries ranging from 75.5% to 94.7% for the various methods examined. Results indicated the best SPE method for the concentration of erythromycin from water was a method previously used to quantify tylosin published by Kolz et al. (2006) with 94.7% recovery. Extraction of erythromycin was performed from sand employing various solvents and buffers to determine the best methods for extraction of the compound from sediment. Two sandy loam pond sediments, one each from Iowa and Oklahoma, were examined in this study utilizing the best erythromycin extraction recoveries from sand. Various extraction times were also examined, and all extraction procedures were performed in duplicate. The greatest recovery of 14 C-erythromycin in the Iowa sediment using 0.3 M ammonium acetate at pH 4.2: acetonitrile (15:85, v/v) solution, using a 20minute shake or an 85-minute/ overnight settling followed by a 15-minute shake the following day, with recoveries of 84 ± 3.4%. While the Oklahoma sediment yielded the CHAPTER 3 FATE OF ERYTHROMYCIN IN SURFACE WATER MICROCOSMS, INCLUDING FRESH AND AGED SEDIMENT SYSTEMS

The detection of antibiotics in water and sediment systems is of concern due to the potential adverse effects which could be associated with their environmental fate. The central aim of this study was to evaluate the fate of erythromycin in microcosms consisting of pond water and submerged pond sediment. The first study examined the dissipation of erythromycin from spiked water and total recovery of [14C]-erythromycin from water and sediment within microcosms ranged between 90.1% and 48% throughout the 63-day study. Erythromycin was reduced in surface water of sediment-containing systems by day 7, which corresponded to an increase of eryrthromycin detected in sediment. In the second study the availability of aged erythromycin was evaluated by incubating sediment with and without a manure amendment with [14C]-erythromycin for 0, 1, 3, or 8 weeks; followed by assessing movement and availability of erythromycin in sediment microcosms after 1, 3, 7, and 14 days. Results indicated differences in residues from aged sediment, with and without manure additions, in extractable residues at day 7 and 14. The addition of manure resulted in greater extractable erythromycin from aged sediments than from sediments without manure. There was a greater release of erythromycin to the water overlying the manure-treated sediments with fresh and 1 week aged sediment than the unamended sediment after 1 and 2 weeks. The results from this experiment demonstrate the ability of manure to influence the fate of erythromycin in environmental matrices. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. The detection of antibiotics in water and sediment systems is of concern due to the potential adverse effects which could be associated with their environmental fate. The central aim of this study was to evaluate the fate of erythromycin in microcosms consisting of pond water and submerged pond sediment. The first study examined the dissipation of erythromycin from spiked water and total recovery of [ 14 C]-erythromycin from water and sediment within microcosms ranged between 90.1% and 48% throughout the 63-day study. Erythromycin was reduced in surface water of sediment-containing systems by day 7, which corresponded to an increase of eryrthromycin detected in sediment. In the second study the availability of aged erythromycin was evaluated by incubating sediment with and without a manure amendment with [ 14 C]-erythromycin for 0, 1, 3, or 8 weeks; followed by assessing movement and availability of erythromycin in sediment microcosms after 1, 3, 7, and 14 days. Results indicated differences in residues from aged sediment, with and without manure additions, in extractable residues at day 7 and 14. The addition of manure resulted in greater extractable erythromycin from aged sediments than from sediments without manure. There was a greater release of erythromycin to the water overlying the manure-treated