Torsten Hahn

Antibiotics as a chemical stressor affecting an aquatic decomposer-detritivore system.

Recent evidence indicates that a variety of antibiotic residues may affect the integrity of streams located downstream from wastewater treatment plants. Aquatic communities comprising bacterial and fungal decomposers and invertebrate detritivores (shredders) play an important role in the decomposition of allochthonous leaf litter, which acts as a primary energy source for small running waters. The aim of the present study was to assess whether an antibiotic mixture consisting of sulfamethoxazole, trimethoprim, erythromycin-H2O, roxithromycin, and clarithromycin has an effect on such a decomposer-detritivore system. Leaf discs were exposed to these antibiotics (total concentration of 2 or 200 microg/L) for approximately 20 d before offering these discs and corresponding control discs to an amphipod shredder, Gammarus fossarum, in a food choice experiment. Gammarus preferred the leaf discs conditioned in the presence of the antibiotic mixture at 200 microg/L over the control discs (pair-wise t test; p = 0.006). A similar tendency, while not significant, was observed for leaves conditioned with antibiotics at a concentration of 2 microg/L. The number of bacteria associated with leaves did not differ between treatments at either antibiotic concentration (t test; p = 0.57). In contrast, fungal biomass (measured as ergosterol) was significantly higher in the 200 microg/L treatment (t test; p = 0.038), suggesting that the preference of Gammarus may be related to a shift in fungal communities. Overall these results indicate that mixtures of antibiotics may disrupt important ecosystem processes such as organic matter flow in stream ecosystems, although effects are likely to be weak at antibiotic concentrations typical of streams receiving wastewater treatment plant effluents.

Environmental chemicals with known endocrine potential affect yolk protein content in the aquatic insect Chironomus riparius

The use of vitellogenesis as a marker for possible effects of endocrine disrupting agents on insects was tested in the aquatic midge Chironomus riparius. As test substances the synthetic ecdysoid tebufenozide, and the endocrine disruptors bisphenol a and 4-n-nonylphenol were applied in a semi-static manner. The yolk protein contents of freshly emerged (24 h) male and female midges were determined by an ELISA procedure. In males, where always low amounts of immunoreactivity were apparent, yolk concentrations were lowered by 10% after a 80 microg/l tebufenozide treatment, and by 20-25% after exposition to bisphenol a at concentrations of 1, 100, and 3,000 microg/l. 4-n-nonylphenol contamination caused an inverted dose-response curve. At low test concentrations (1.9-30 microg/l) reduced yolk immunoreactivity occurred, while at medium concentrations (120 and 500 microg/l) no significant effects were observable. In the most highly contaminated group (2,000 microg/l) yolk protein immunoreactivity was elevated to 107% of the control. Female yolk protein contents were affected only in the 3,000 microg bisphenol a/l contaminated group, where yolk immunoreactivity was reduced by ca. 10% compared to the control.

Indirect Effects of Antibiotics in the Aquatic Environment: A Laboratory Study on Detritivore Food Selection Behavior

ABSTRACT With regard to possible detrimental effects of human and veterinary antibiotics in the aquatic environment, most research in this field assesses direct impacts of pharmaceuticals on vertebrate or invertebrate test organisms. Another related area of concern is the possible development of antibiotic-resistant bacteria by introducing antimicrobials into the aquatic compartment. However, indirect effects of antibacterials on the trophic cascade have rarely been investigated. This study contributes with an example of how indirect effects of antibiotics on leaf litter decay can be measured and to what extent shredder organisms might be affected. Results from food-selection experiments using Gammarus pulex (Amphipoda) demonstrated clear preferences for leaves conditioned in the absence versus those conditioned in the presence of two antibiotics, oxytetracycline and sulfadiazine. Although this result suggested that microbial and fungal colonisation during leaf litter conditioning might be adversely affected in the antibiotic-treated groups, analyses of total carbon and nitrogen content of conditioned leaf discs did not reveal differences among the treatments.

Antibiotic mixture effects on growth of the leaf-shredding stream detritivore Gammarus fossarum

Pharmaceuticals contribute greatly to human and animal health. Given their specific biological targets, pharmaceuticals pose a significant environmental risk by affecting organisms and ecosystem processes, including leaf-litter decomposition. Although litter decomposition is a central process in forest streams, the consequences of exposure to pharmaceuticals remain poorly known. The present study assessed the impact of antibiotics as an important class of pharmaceuticals on the growth of the leaf-shredding amphipod Gammarus fossarum over 24 days. Exposure scenarios involved an antibiotic mixture (i.e. sulfamethoxazole, trimethoprim, erythromycin-H2O, roxithromycin, clarithromycin) at 0, 2 and 200 µg/L to assess impacts resulting from exposure to both water and food. The antibiotics had no effect on either leaf-associated fungal biomass or bacterial abundance. However, modification of leaf quality (e.g. through shifts in leaf-associated microbial communities) may have triggered faster growth of gammarids (assessed in terms of body mass gain) at the low antibiotic concentration relative to the control. At 200 µg/L, however, gammarid growth was not stimulated. This outcome might be due to a modified ability of the gut microflora to assimilate nutrients and carbon. Furthermore, the observed lack of increases in the diameter of the gammarids’ peduncles, despite an increase in gammarid mass, suggests antibiotic-induced effects in the moulting cycle. Although the processes responsible for the observed effects have not yet been identified, these results suggest a potential role of food-quality, gammarid gut microflora and alteration in the moulting cycle in mediating impacts of antibiotics on these detritivores and the leaf decomposition process in streams.

Reducing uncertainty in environmental risk assessment (era): clearly defining acute and chronic toxicity tests

Intent. The intent of Learned Discourses is to provide a forum for open discussion. These articles reflect the professional opinions of the authors regarding scientific issues. They do not represent SETAC positions or policies. And, although they are subject to editorial review for clarity, consistency, and brevity, these articles are not peer reviewed. The Learned Discourses date from 1996 in the North America SETAC News and, when that publication was replaced by the SETAC Globe, continued there through 2005. The continued success of Learned Discourses depends on our contributors. We encourage timely submissions that will inform and stimulate discussion. We expect that many of the articles will address controversial topics, and promise to give dissenting opinions a chance to be heard. Rules. All submissions must be succinct: no longer than 1,000 words, no more than 6 references, and at most one table or figure. Reference format must follow the journal requirement found on the Internet at http:// www.setacjournals.com. Topics must fall within IEAM’s sphere of interest. Submissions. All manuscripts should be sent via email as Word attachments to Peter M Chapman (peter_chapman@golder.com).

Emission of biocides from hospitals: comparing current survey results with European Union default values.

Under the European Union (EU) Biocidal Products Directive 98/8/EC, comprehensive evaluations on substances of the Third Priority List were conducted until 31 July 2007. This list includes, among other categories, disinfectants for human hygiene (e.g., skin and surface disinfection). For environmental exposure assessment of biocides, the EU emission scenarios apply. Currently available default values for disinfectants are based on consumption data from not more than 8 hospitals and were originally assembled for other purposes. To revalidate these default values, a survey on annual consumption data was performed in 27 German hospitals. These data were analyzed to provide consumption data per bed and day and per nurse and day for particular categories of active ingredients and were compared with default values from the EU emission scenario documents. Although several deviations were detected, an overall acceptable correspondence between Emission Scenario Documents default values and the current survey data was found.