Bent Halling-Sørensen

Acute and chronic toxicity of veterinary antibiotics to Daphnia magna

The acute and chronic toxicity of nine antibiotics used both therapeutically and as growth promoters in intensive farming was investigated on the freshwater crustacean Daphnia magna. The effect of the antibiotics metronidazole (M), olaquindox (OL), oxolinic acid (OA), oxytetracycline (OTC), streptomycin (ST), sulfadiazine (SU), tetracycline (TC), tiamulin (TI) and tylosin (TY) was tested in accordance to the ISO (1989) and OECD (1996) standard procedures. The acute toxicities (48-h EC50 value, mg/l) in decreasing order were OA (4.6), TI (40), SU (221), ST (487), TY (680) and OTC (approximately 1000). NOECs were 340 mg/l for TC and 1000 mg/l for M and OL. Toxic effect on reproduction occurred generally at concentrations, which were one order of magnitude below the acute toxic levels. The chronic toxicity (EC50 values, mg/l) in the D. magna reproduction test in decreasing order were TI (5.4), SU (13.7), TC (44.8) and OTC (46.2). The NOECs (mg/l) obtained in the reproduction test with OA, ST, TY and M were 0.38 for OA, 32 for ST, 45 for TY and 250 for M. The observed toxicity of OA to D. magna indicates that this substance, which is a commonly used feed additive in fish farms, has a potential to cause adverse effects on the aquatic environment.

Algal toxicity of antibacterial agents used in intensive farming.

The growth inhibiting effects of eight antibiotics used either therapeutically or as growth promoters in intensive farming on two species of micro algae, Microcystis aeruginosa (freshwater cyanobacteria) and Selenastrum capricornutum (green algae) were investigated. The effects of the antibiotics benzylpenicillin (penicillin G) (BP), chlortetracycline (CTC), olaquindox (O), spiramycin (SP), streptomycin (ST), tetracycline (TC), tiamulin (TI) and tylosin (TY) were tested in accordance with the ISO 8692 (1989) standard protocol. Algal growth was measured as increase in chlorophyll concentration by extraction with ethanol followed by measurement of fluorescence. Results were quantified in terms of growth rates using the Weibull equation to describe the concentration response relationship. The toxicity (EC50 value, mg/l) in alphabetic order were BP (0.006); CTC (0.05); O (5.1); SP (0.005); ST (0.007); TC (0.09); TI (0.003) and TY (0.034) for M. aeruginosa. BP (NOEC = 100); CTC (3.1); O (40); SP (2.3); ST (0.133); TC (2.2); TI (0.165) and TY (1.38) for S. capricornutum. In this investigation M. aeruginosa is found to be about two orders of magnitude more sensitive than S. capricornutum. It was observed that most of the compounds were unstable during the test period due to hydrolysis and photolysis.

Quantitative analysis of oxytetracycline and its impurities by LC-MS-MS

A liquid chromatographic-tandem mass spectrometric method using an Xterra MS C(18) chromatographic column ( 100 mm x 2.1 mm i.d., 3.5microm) that allows complete separation of oxytetracycline (OTC) and the impurities: 4-epi-oxytetracycline (EOTC), tetracycline (TC), 4-epi-tetracycline (ETC), 2-acetyl-2-decarboxamido-oxytetracycline (ADOTC), alpha-apo-oxytetracycline (alpha-AOTC) and beta-apo-oxytetracycline (beta-AOTC) was developed. Gradient elution was used and calibration curves were obtained using the scan mode selected reaction monitoring (SRM). Acceptable correlations were obtained for OTC, TC, EOTC and ADOTC whereas the correlations of alpha-AOTC and beta-AOTC were less accurate resulting in higher limits of quantification (LOQ) and limits of detection (LOD) relative to the other compounds. The intraday and interday accuracy varied for all the compounds from 90 to 112% and the intraday and interday precision were lower than 7.1%. The method was applied for analysis of commercial available ointments containing OTC resulting in an acceptable quantification of OTC and the impurities in the drug preparations. The advantage of this method compared to the other separation methods is an empty separation window right after the large peak corresponding to OTC in the chromatogram, which facilitates an accurate determination of ADOTC and the other impurities.

Evaluation of elemental composition of algal biomass as toxical endpoint

Freeze dried algal biomass was analysed with an organic elemental analysis (CHNS) in order to determine whether chemical stress could be detected as changes in gross cellular composition. Results showed that an LOEC for potassium dichromate of 0.21 mg/l was statistically different from a NOEC of 0.10 mg/l. The elemental analysis method could be improved if the final algal density in the batch cultures was kept low (<105 cell/ml). The remaining problem is to get sufficient biomass to perform the elemental analysis. The study demonstrates the potential of elemental analysis applied as endpoint for algal toxicity and defines the optimal conditions for simultaneous CHNS determination, furthermore proposals for future investigations are given.

A model of nitrogen removal from waste water in a fixed bed reactor using simultaneous nitrification and denitrification (SND)

Abstract A model predicting the effluent nitrogen concentration of treated waste water in an submerged fixed bed reactor using clinoptilolite clay as matrix, is presented. By this treatment oxidation of organic material, nitrification and denitrification, by three different classes of bacteria, occurs in the same environment. The occurrence of these three processes within a close environment resemble too some extent the way the processes take place in aquatic sediment, which also to some extent consists of clay. The results presented in this paper show that it is possible to simulate the simultaneous nitrification and denitrification (SND) processes with a model which containing 6 state-variables including a coupling of the 3 processes performed by each of the bacterial species included. The model results and the results obtained from experimental data are in general comparable.