In Vitro Test Of Antibacterial Agents Used in Intensive Farming

Antibacterial agents may be considered environmental micropollutants because of they are developed with the intention of performing a biological effect and have many of the necessary properties to bioaccumulate and provoke effects in the ecosystem. The antibacterial agents are greatly used in intensive farming for therapeutic and prophylactic purpose and the manure used as fertiliser directly applied on fields may contain these pharmaceutical substances that will end up first in the terrestrial ecosystem and then in the aquatic one. The antibacterial agents commonly used in Italy are oxitetracycline (OT), sulphametazine (SM) and tylosin (TY). The toxic effect data (EC50) of antibacterial agents on various aquatic species found in the literature (Macri et al., 1988; Wollenberger et al., 2000) shows values in the mg/l range and the investigations have primarily been done on crustaceans and fish rather than algal species. The few tests carried out using as test organisms algal species show on the other hand that algae are very sensitive to antibacterial agents (Holten Lutzhoft et al., 1999) Aim of this study was to perform acute toxicity test using as sensible model a freshwater green alga. The growth-inhibiting effects of OT, SM and TY were investigated by a modified test procedure based on the procedure described in the ISO 8692 (1989) protocol on the freshwater green alga Selenastrum capricornutum. The compounds were tested at 8 concentration levels without replicates in a range of 1-25 mg/l for SM, 0,1-5 mg/l for TY and 1-10 mg/l for OT, whereas the controls were grown in six replicates. The number of tests was at least three. Algal growth was measured as increased chlorophyll concentration by extraction with ethanol followed by measurement of fluorescence (excitation wavelength = 430 nm, emission wavelength = 671 nm). Results were quantified in terms of growth rates using Weibull equation (Nyholm et al., 1992) to describe the concentration response relationship. The toxicity (EC50 value, mg/l) were: OT, 4,17; SM, 10,7;TY, 0,949. Although tylosin is the most toxic agent (EC50 = 0,949 mg/l) experimental data shows that it is the one with the shortest DT50 among those assayed. References H-C. Holten Lutzhoft et al.: Arch. Environ. Contam. Toxicol. (1999) 36, 1-6. ISO 8692 (1989). A. Macri et al.: Ecotoxicol. Environ. Safety (1998) 8, 101-105. N. Nyholm et al.: Environ. Toxicol. Chem. (1992) 11, 157-167. L. Wollenberger et al.: Chemosphere (2000) 40, 723-730.