Oxytetracycline as environmental contaminant in arable lands

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Abstract

Oxytetracycline (OXY) is a broad-range antimicrobial routinely used in pig production, at doses in the range of few g/kg of medicated feed, during the weaning period. It could persist at ppm level in pig liquid manure that routinely is used for organic fertilisation. In the present work we describe a methodology to study OXY environmental fate in arable land where crops are cultivated for animal feeding purposes. A liquid-liquid extraction followed by metal chelate affinity chromatography was applied to environmental samples of manures and soils drawn within a case-control study. Extracts were then analysed by high performance liquid chromatography with UV/DAD detection, using a reverse phase column, and expressing the results as 4-epioxytetracycline epimer. Results indicate OXY is well retained at mg kg−1 levels in soil exposed to contaminated pig manure fertilisation. Such compartment could constitute an abiotic reservoir for the systemic and/or for the external contamination of corn.

Introduction

Antimicrobial drugs utilized in intensive farming can impact on environmental compartments such as water and/or soil. Tetracyclines are among the most used in pig farming and previous studies demonstrated their persistence in manure and soil [1], [2], [3] and possible exposition of farmers during application of organic fertilizers to soil [4].

The debate on antibiotics environmental fate is reinforced by the concern on induction/selection of microbial resistance and by the possible ecosystem alterations, such as colonisation from fungi and yeasts, and inhibition of natural bacterial communities [5]. As regard tetracyclines, they have the highest capability to bind organic matter [6] if compared to other antimicrobials, and thus they usually locate in the top layer of soil, within the first 40 cm depth.

Recently, during on farm routine controls, carried out with fluorimetric spectroscopy [7], on on-farm produced feeds, it was found that corn seeds for pig nutrition were tetracycline contaminated (Fig. 1). Further analysis confirmed the presence of oxytetracycline at low ppm value. Such cross-contamination phenomena usually happen, at feed mill level, as consequence of medicated and not medicated feeds production on the same line [8].

In this case, the feed material was originated directly from the field; the question was whether the presence of tetracyclines could arise as a result of (i) soil dust contamination during harvesting or (ii) systematic absorption by plant roots from soil.

To deepen the matter, a pilot study was set up in the field, were corn was cultivated and fertilized with different slurries coming from OXY treated and untreated pigs.

Section snippets

Experimentals

Standards and reagents: oxytetracycline and its 4-epimer were purchased from Sigma–Aldrich Chemie Gmbh, Germany. Acetonitrile, and other chemicals were of the highest purity grade from Carlo Erba, Italy. Metal chelating sepharose fast flow was from Amersham Biosciences, UK; SPE box from Supelco. Rotary Evaporator (Buchii, Swiss), Ultrasonic bath, Bransonic 321 refrigerated centrifuge (Alc, Italy) and Beckmann Coulter high performance liquid chromatography (HPLC)-UV-DAD system gold were also

Analytical performances

The limit of detection (Lod) on the basis of signal-to-noise ratio of control samples was estimated 20 ng g−1; the recoveries, along with repeatability (CVr) and reproducibility (CVR) data, resulted to be quantitative for all the matrices and the experimental points considered, with no significant mismatches (Table 1).

Results of the analyses of each incurred sample from contaminated and control series, respectively, are reported in Table 2. OXY residues were found in both slurries and soils; in

Discussion

Because OXY is excreted in faeces and urine also as 4-epimer, [11] and because such epimerisation is facilitated from pH environment around 6 [12], such as that in slurries and organically fertilised soils, the analytical strategy was addressed to transform the residual untransformed OXY in its 4-epimer. This was reached by storing the extracts in aqueous solution for more than 3 days at −20 °C [13]. The results of our trials confirm the environmental persistence of high oxytetracycline

Acknowledgement

Work supported by Regione Emilia Romagna grant, Assessorato alle Politiche Agricole e Ambientali: CRPA 2005 project.

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