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The influence of the use of antibiotics on the prevalence of resistance genes in the environment is still poorly understood. We studied the diversity of tetracycline and sulfonamide resistance genes as influenced by fertilization with pig manure in soil microcosms and at two field locations. Manure contained a high diversity of resistance genes, regardless of whether it stemmed from a farm operation with low or regular use of antibiotics. In the microcosm soils, the influence of fertilization with manure was clearly shown by an increase in the number of resistance genes in the soil after manuring. Spiking of the tetracycline compounds to the microcosms had only little additional impact on the diversity of resistance genes. Overall, the tetracycline resistance genes tet(T), tet(W), and tet(Z) were ubiquitous in soil and pig slurries, whereas tet(Y), tet(S), tet(C), tet(Q), and tet(H) were introduced to the microcosm soil by manuring. The diversity of tetracycline and sulfonamide [sul(1), sul(2), and sul(3)] resistance genes on a Swiss pasture was very high even before slurry amendment, although manure from intensive farming had not been applied in the previous years. The additional effect of manuring was small, with the tetracycline and sulfonamide resistance diversity staying at high levels for the complete growth season. At an agricultural field site in Germany, the diversity of tetracycline and sulfonamide resistance genes was considerably lower, possibly reflecting regional differences in gene diversity. This study shows that there is a considerable pool of resistance genes in soils. Although it is not possible to conclude whether this diversity is caused by the global spread of resistance genes after 50 years of tetracycline use or is due to the natural background in soil resistance genes, it highlights a role that environmental reservoirs might play in resistance gene capture.

In the past decade the list of chemicals in the environment that are able to mimic the natural hormone estrogen, thereby disrupting endocrine function, has grown rapidly. These chemicals are able to bind to estrogen receptors (ERs) and influence estrogen signalling pathways, although several of them have structures that differ substantially from the endogenous hormone 17beta-estradiol. In this study, six extensively used ultraviolet (UV) filters were assessed for transcriptional activation of estrogen receptors. Because of their high lipophilicity, these UV filters tend to bioaccumulate in the environment. They have been found in surface waters, fish, and in human milk fat. Using a sensitive in vitro reporter gene assay, we found that all six compounds induce estrogenic activity towards ERalpha, while four out of six compounds induced transcriptional activity of ERbeta. Zebrafish, in which an estrogen responsive luciferase reporter gene has been stably introduced, were used for in vivo testing. In this transgenic zebrafish assay none of the compounds showed estrogenic activity. Our findings suggest that one should be aware of over-interpretation when predicting in vivo effects from weak in vitro data. However, it can not be ruled out that these UV filters have long-term effects in the environment.

In vitro induction of ethoxyresorufin O-deethylase (EROD) activity in cell cultures is an extensively validated tool for measuring overall potencies of mixtures of halogenated aromatic hydrocarbons (HAHs) in samples from the abiotic or biotic environment. For risk assessment with special attention to effects in wild birds, an assay was developed that makes use of chicken embryo hepatocytes. However, it was questioned whether compound-specific responses are consistent at the various developmental stages. The results of our present study show that there are considerable differences between early and late embryonal and post-hatching stages. The induction of EROD was measured in primary chicken hepatocyte cultures. The cells were isolated at day 14 and day 19 of embryonal development and at day 1 post hatching. Hepatocytes were exposed in vitro to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126, IUPAC nomenclature) and 2,3',4,4',5-pentachlorobiphenyl (PCB 118). The respective compounds were chosen as representatives for dioxins, furans, non-ortho PCBs, and mono-ortho PCBs. These groups of chemicals have been identified as environmental contaminants with major dioxin-like effects that are mediated by a common receptor, the arylhydrocarbon (Ah) receptor. At all developmental stages, TCDF was more potent than TCDD. Relative potencies (RP = EC50TCDD/EC50HAH) decreased in the order TCDF < TCDD < PCB 126 < PCB 118. Depending on the developmental stage, TCDF was 1.2 to 3.4 times more potent than TCDD. PCB 126 was equipotent or less potent by a factor of 3 than TCDD. PCB 118 was 100 to 300 times less potent than TCDD. Both the mean effective concentration (EC50) and the maximum EROD activity (Ymax) of all compounds were lower in hepatocyte cultures from 14-day-old embryos than those from 19-day-old embryos or 1-day-old hatchlings. RPs were comparable in 19-day-old embryos and in hatchlings, but significantly different in 14-day-old embryos.

2,2',4,4',5,5'- (PCB 153), 2,3,3',4,4',5- (PCB 156) and 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) were administered orally to three groups of C57BL/6J mice using single doses of 1.5-109.1 mg/kg. Two other groups of mice received binary mixtures of PCB 153 and 156 or PCB 153 and 169. The hepatic deposition, elimination, CYP1a and CYP2b dependent enzyme activities were studied during a 77-day period. Some interactive effects on hepatic deposition and elimination were observed, resulting in increased deposition and faster elimination. These effects were most pronounced for the PCBs 156 and 169. A potentiating effect on hepatic CYP1a dependent 7-ethoxyresorufin-O- deethylation (EROD) activity was observed for the combination of PCB 156 and 153. Based on the results from the present study and earlier studies, it is suggested that the potentiating effect on EROD activity might be caused by a mechanism that is governed by at least two factors. The first is a toxicokinetic modulation of hepatic retention. The second factor is probably an elevation of hepatic Ah receptor levels by PCB 153.

Six groups of C57BL/6J mice received single oral doses of 1.5-10.6 nmol/kg 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PnCDD), 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (HxCDD) or 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) as single compounds or in combination with 300 mumol/kg 2,2',4,4',5,5'-hexachlorobiphenyl (HxCB). Two other groups of mice received a mixture of the first three compounds, either with or without HxCB. The hepatic deposition and elimination of the compounds and their CYP1a dependent 7-ethoxyresorufin-O-deethylation (EROD) activity were studied until day 175. Interactive effects on the hepatic deposition of PnCDD were observed in most of the mixed dose groups. For HxCDD and PnCDF interactive effects were either very small or absent. No interactive effects were observed on hepatic elimination rates of PnCDD, HxCDD or PnCDF. No evidence was found for the influence of HxCB cotreatment on the hepatic concentration-response curves of the three compounds or their mixture. Based on the results from the present study it is concluded that PCDDs, PCDFs and PCBs may influence each other's, toxicokinetics when administered in mixtures.

Changes in the popliteal lymph node (PLN) in mice evoked by a local graft-versus-host (GVH) reaction and by a single injection of various agents into the hind footpad were compared. The drug diphenylhydantoin induced similar weight changes in time as the GVH reaction. More vigorous and protracted reactions were induced by the drug nitrofurantoin and the contact sensitizer dinitrochlorobenzene, whereas the antigens lipopolysaccharide and sheep erythrocytes caused very moderate and short-lasting weight changes. Alterations of lymph node architecture upon injection of diphenylhydantoin resembled those observed during the GVH response. Some quantitative and qualitative differences were noted for nitrofurantoin, but clearly deviant morphological alterations were seen in response to lipopolysaccharide and sheep erythrocytes. The PLN reaction to dinitrochlorobenzene had features of both the GVH reaction and the antigen-induced responses. These findings support the concept that some drugs and chemicals may induce or exacerbate lymphoproliferative disorders by GVH-like mechanisms.