The toxicity of antibiotic agents to the luminescent bacterium Vibrio fischeri.

Despite their common use the fate and effects of antibiotics in the environment are largely unknown. These compounds may enter the environment through different pathways, resulting in the contamination of waste water or fresh water, where bacteria are most likely the primarily affected organisms. In this paper the toxicity of several drugs, reflecting the most important groups of antibiotics and chemotherapeutics, towards Vibrio fischeri are presented. The chronic bioluminescence inhibition assay with Vibrio fischeri is shown to be sensitive against many of the high volume antibiotics used for veterinary purposes and in aquaculture. Thus the assay may be a valuable tool for an effects assessment and biomonitoring of these xenobiotics. The available data for both parts of the risk assessment procedure--exposure assessment and effects assessment--have to be regarded as insufficient for most antibiotics. When the available data about environmental concentrations of antibiotics are compared with their toxicity towards Vibrio fischeri, direct effects on natural microbial communities are to be expected.     

Toxicity testing with Vibrio Fischeri: A comparison between the long term (24 h) and the short term (30 min) bioassay

The acute bioluminescence inhibition assay using the marine bacterium Vihrio fischeri as the test organism is a widely used short term toxicity test. This paper compares the standard 30 minutes test with a 24 h assay using the same organism and the same test parameter. For that purpose concentration-response relationships were determined for a set of selected substances, reflecting different modes and mechanisms of action.

The results indicate a severe blind spot of the acute biotest: The toxicity of certain specifically acting chemicals is drastically underestimated here, while the chronic biotest gives a more reliable estimate of the toxicity of these substances.     

Characterization of industrial aqueous discharges by the TLC/Ames’ assay

The $\text{in situ}$ detection of mutagens by the TLC/Ames’ assay has been applied to aqueous discharges from a textile plant. The samples were fractionated in acid/neutral and basic fractions which subsequently were subject to the TLC/Ames’ test. The results demonstrate the presence of a number of both direct and indirect mutagens in the waste water. The chemical properties of these compounds are discussed in light of their chromatographic behaviour. The applicability of this method for characterizing mutagens in complex mixtures is demonstrated.     

Bioassays with Vibrio fischeri for the assessment of delayed toxicity

The standardized bioluminescence assay with Vibrio fischeri underestimates the aquatic toxicity of chemicals which interfere with metabolic pathways supporting long term processes like growth and reproduction due to its short incubation time (30 min). Therefore this short term assay was compared with two alternative bioassays with prolonged incubation times using the same test organism: the growth inhibition assay (7 h) and the long term bioluminescence assay (24 h). Two sets of compounds were selected to reflect acute and delayed toxicity. The first group comprised pentachlorophenol, dodecylpyridiniumbromide and 3,4-dichloroaniline and the second nalidixic acid, chloramphenicol and streptomycinsulfate. The effects of compounds with acute toxicity are determined with similar sensitivity in all bioassays. Substances with delayed toxicity show only minor or no toxicities in the standardized short term bioassay but severe effects in both long term bioassays independent of the parameter used. It is concluded that the standardized short term bioluminescence assay exhibits serious limitations for the assessment of aquatic toxicity. The long term bioassays, however, may help to overcome these limitations.     

Kombinationswirkungen von Umweltchemikalien in der Ökotoxikologie

Ecosystems and biocoenoses are exposed to multiple mixtures of environmental pollutants, but the usual risk assessment of chemical toxicities is focussed only on the judgement of single substance toxicity. With the two biometrical models concentration-addition and independent action known from pharmacology and toxicology, a pragmatic way for the analysis of combined effects is possible using the experimental knowledge of single substance toxicity. A short introduction to the models is given and an appropriate experimental design for mixture toxicity analysis is outlined. The principal suitability of the concepts was verifed in two different bioassays (green alga; luminescent bacterium) with the analysis of binary and multiple mixture toxicities of environmental chemicals. In this paper we present the results obtained with the green algae bioassay. Congruent results from the bioluminescence inhibition assay can be found in Grimme (1998). The results obtained indicate that the toxicities of mixtures of chemicals can be studied experimentally, even at low concentrations of the individual components. Mixture toxicities were detected at low, statistically non-significantly acting concentrations of the single compounds. These results force one to take mixture toxicities into account when environmental standards are established.     

Time-dependent toxicity in the long-term inhibition assay with Vibrio fischeri

The significance of the duration of exposure for the detection of toxicity was evaluated in a 24 h long-term bioluminescence inhibition assay with Vibrio fischeri. Bioluminescence was measured over the time course of 24 h using microplates. The undisturbed luminescence of controls in this assay exhibited characteristic dynamics: a decrease within a period of 12 h with minimal luminescence followed by a continuous increase of luminescence beyond the starting value. To evaluate the toxic influence of compounds chosen to reflect immediate and delayed toxicity to V. fischeri, the bioluminescence was measured for 24 h at 30 min intervals. Luminescence inhibition patterns were recorded for subdinoseb, pentachlorophenol and 2,4,5-trichlorophenol) and for substances causing delayed toxicity (chloramphenicol, nalidixic acid and phosphomycin). The toxic influence of substances with immediate toxicity was observed directly after application, whereas the toxicity patterns of substances with delayed toxicity developed specifically over the time according to the different involved mechanisms of action. It is concluded that knowledge about time to toxicity in bioassays is necessary in order to identify suitable test endpoints as well as to recognize potential hazards related to time-dependent toxicity.