A.T.C. Bosveld

Effects of polyhalogenated aromatic hydrocarbons (PHAHs) on biochemical parameters in chicks of the common tern (Sterna hirundo)

Abstract Common tern ( Sterna hirundo ) eggs were collected from eight breeding colonies that differed in degree of polyhalogenated aromatic hydrocarbon (PHAH) pollution. The eggs were artificially incubated and the chicks sacrificed within 12 hours after hatching. Plasma thyroid hormones (total thyroxine (TT4), free thyroxine (FT4) and triiodothyronine (TT3)), hepatic T4-glucuronyltransferase (T4-UGT) activity, plasma retinol and yolksac retinoid levels were measured and compared with yolksac PHAH residues and hepatic ethoxyresorufin- and pentoxyresorufin- O -deethylase (EROD and PROD) activities. The yolksac PHAH residues measured were polychlorinated biphenyl (PCB), polychlorinated dibenzofuran (PCDF) and polychlorinated dibenzo- p -dioxin (PCDD). No significant differences were observed between colony average levels of plasma thyroid hormones (TT4, FT4 and TT3) nor plasma retinol levels and T4-UGT activities that could be related to colony average PHAH levels. However, average colony yolksac retinyl ester levels did show significant differences. When correlated for individual terns, significant correlations between all these parameters and PHAH levels or EROD or PROD activities were found. The correlation between hepatic T4-UGT and EROD and PROD activities was very strong, suggesting a concomitant induction of these drug metabolizing enzymes. The PHAH levels were expressed as dioxin equivalents (TEQs) based on toxic equivalence factors (TEFs) as proposed by Safe (1990, 1994). In addition to plasma retinol, another retinoid was found which resembles 3,4-didehydro-retinol (vitamin A2) in chromatographic and spectroscopic behaviour. This putative plasma vitamin A2 was significantly positive correlated with the yolksac TEQs and with the hepatic EROD activity. Esters of both retinol and putative vitamin A2 were detected in the yolksac. The average yolksac vitamin A2 levels of the cleanest Zeewolde colony were significantly higher than the average levels in the other colonies.

Inhibition of ethoxyresorufin-O-deethylase (EROD) activity in mixtures of 2,3,7,8-tetrachlorodibenzo-p-dioxin and polychlorinated biphenyls

Induction of ethoxyresorufin-O-deethylase (EROD) activity and porphyrin accumulation shows different structure-activity relationships for different polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Interactions between the two responses can strongly influence the induction and activity of EROD. The results support the conclusion that there are nonadditive interactions between nondioxin-like PCBs and dioxin-like compounds. The interaction between EROD activity and the porphyrin biosynthesis makes the prerequisite of additivity in the toxic equivalency factor concept for environmental mixtures highly spurious. Inhibition of EROD activity caused by non-dioxin like compounds could have a significant impact on the value of EROD activity as a biomarker in the present methods of risk assessment for these compounds.

Biomarkers and bioassays as alternative screening methods for the presence and effects of PCDD, PCDF and PCB

SummaryPolyhalogenated aromatic hydrocarbons (PHAH) are wide spread, highly toxic, environmental contaminants. As such they pose risks for both humans and wildlife. For risk assessment purposes, concentrations are generally analyzed by HRGC-HR/LRMS. With the analytical data, mixture toxicity is calculated using the TEF concept. With this method only the defined congeners are taken into account and additivity for all congeners is assumed, whereas synergistic and antagonistic effects for several PCDD/F in combination with PCB have also been reported. To avoid these problems and high analytical costs, bioassays can be used for screening purposes. Cytochrome P450 1 A 1 induction and vitamin A and thyroid hormone levels are shown to be useful markers for PHAH exposure. When bioassays based on cytochrome P450 1A1 induction, in cultured cells, in multi-well culturing plates, are used, 2,3,7,8-TCDD detection limits <0.2 pg are possible. As such these bioassays are highly sensitive, cost effective and time saving. This application can be used as a pre-screening method to determine total “dioxin” content of environmental samples.

Occurrence and effects of PCBs, PCDDs and PCDFs in hatchlings of the common tern (Sterna hirundo)

Abstract From eight common tern (Sterna hirundo) colonies eggs were collected for laboratory incubation. Significant differences between colonies were found for yolk sac concentrations of polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). Corresponding differences were observed for hepatic EROD and PROD activities. No differences between the colonies were observed regarding embryonic O 2 CO 2 exchange, egg weight, eggshell thickness, hatchling weight or liver weight/body weight ratio. It is concluded that hepatic EROD activity is usable as a relative sensitive biochemical indicator for early exposure to planar halogenated polyaromatics in the early life stage of the common tern.

Ethoxyresorufin O-deethylase (EROD) inducing potencies of planar chlorinated aromatic hydrocarbons in primary cultures of hepatocytes from different developmental stages of the chicken

Abstract 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 representives 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.