Veterinary antibiotics administered to livestock are excreted as feces, and antibiotics that remain in feces are mainly introduced into the soil in the form of livestock compost. Antibiotics that remain in the soil are run?off to surface water or leached into underground water during rainfall, causing problems such as antibiotic contamination or the occurrence of antibiotic resistant bacteria.
In this study, the analysis method for detecting residual veterinary antibiotics in river water and soil in agricultural environment was developed and the occurrence of residual antibiotics was monitored. In this study, 12 types of livestock antibiotics were selected for analysis. River water samples were adjusted to pH 2.5±0.1 using 40 % (v/v) sulfuric acid, followed by 5 % (w/v) Na2-EDTA, and soil samples were added with McIlvain buffer of pH 4.0 and Na2-EDTA to extract residual antibiotics in soil into liquid form. Afterwards, river water samples and liquid-extracted samples, solid-phase extraction (SPE) using HLB cartridge was used to preprocess the samples. Instrument analysis conditions were optimized for effective separation and quantitative analysis of selected antibiotics. In the analysis of liquid chromatography, the mobile phase uses HPLC?grade water (A) and acetonitrile (B) containing 0.1 % (v/v) formic acid, and C18 (3.5 μm, 4.6 ×150 mm) column was used for analysis under gradient conditions. Analyzing mass spectrometers, ionization was used using electrospray ionization (ESI) method and multiple reaction monitoring (MRM) condition was established by checking precursor ion and production ion in positive ion mode.
The residual antibiotic analysis method developed in this study was validated for linearity, specificity, matrix effect, recovery, and precision, and subsequently calculated method detection limits (MDL) and limit of quantitation (LOQ). The specificity verification found no disturbing peak near the retention time of the antibiotic under analysis. As a result of the linearity and recovery rate test, amoxicillin and spiramycin were excluded from the analysis because the calibration curve was not drawn up in the water quality and soil samples and the recovery rate was within the range of 6.4?59.1%. For all other antibiotics, the analysis method was verified and the method detection limit (river water, 0.002?0.012 μg L-1, soil 0.001?0.013 μg kg-1,) and minimum quantitation limit (river water, 0.007?0.039 μg L-1, and soil 0.004?0.042 μg kg-1) were calculated using the optimal analysis method.
Using the developed analysis method, residual antibiotics were analyzed by collecting river water, sediment and soil samples from five sites near Muhan Stream in Yesan-gun, Chungcheongnam-do. Of the total 10 antibiotics, seven antibiotics were detected except ampicillin, penicillin G, and sulfadiazine, and the concentration range was 0.014±0.003-0.309 ±0.077 μg L-1 in river water, 1.45±0.05-9.04 μg kg-1 in sediment, and in soil, 5 sulfamethazine was detected in site 5. The results of this study are expected to be used as basic data for residual livestock antibiotic analysis methods in various mediums in the agricultural environment in the future.