Bert-Ove Lund

Cumulative health risk assessment of 17 perfluoroalkylated and polyfluoroalkylated substances (PFASs) in the Swedish population.

Humans are simultaneously exposed to a multitude of chemicals. Human health risk assessment of chemicals is, however, normally performed on single substances, which may underestimate the total risk, thus bringing a need for reliable methods to assess the risk of combined exposure to multiple chemicals. Per- and polyfluoroalkylated substances (PFASs) is a large group of chemicals that has emerged as global environmental contaminants. In the Swedish population, 17 PFASs have been measured, of which the vast majority lacks human health risk assessment information. The objective of this study was to for the first time perform a cumulative health risk assessment of the 17 PFASs measured in the Swedish population, individually and in combination, using the Hazard Index (HI) approach. Swedish biomonitoring data (blood/serum concentrations of PFASs) were used and two study populations identified: 1) the general population exposed indirectly via the environment and 2) occupationally exposed professional ski waxers. Hazard data used were publicly available toxicity data for hepatotoxicity and reproductive toxicity as well as other more sensitive toxic effects. The results showed that PFASs concentrations were in the low ng/ml serum range in the general population, reaching high ng/ml and low μg/ml serum concentrations in the occupationally exposed. For those congeners lacking toxicity data with regard to hepatotoxicity and reproductive toxicity read-across extrapolations was performed. Other effects at lower dose levels were observed for some well-studied congeners. The risk characterization showed no concern for hepatotoxicity or reproductive toxicity in the general population except in a subpopulation eating PFOS-contaminated fish, illustrating that high local exposure may be of concern. For the occupationally exposed there was concern for hepatotoxicity by PFOA and all congeners in combination as well as for reproductive toxicity by all congeners in combination, thus a need for reduced exposure was identified. Concern for immunotoxicity by PFOS and for disrupted mammary gland development by PFOA was identified in both study populations as well as a need of additional toxicological data for many PFAS congeners with respect to all assessed endpoints.

Novel Involvement of a Mitochondrial Steroid Hydroxylase (P450c11) in Xenobiotic Metabolism

Adrenocortical mitochondrial cytochrome P450 isozymes of the Cyp11 family normally synthesize steroids with a very strict substrate specificity. However, for the first time, P450c11 was additionally shown to metabolize and bioactivate the adrenotoxic environmental pollutant 3-methylsulfonyl-2,2-bis(4-chlorophenyl)-1,1-dichloroethene (MeSO2-DDE). This conclusion is based on a striking correlation between inductions of MeSO2-DDE and deoxycorticosterone metabolism by forskolin in the adrenocortical cell lines Y1 and Kin-8, inhibition of P450c11-dependent activities in Y1 cells by MeSO2-DDE, and metabolism of MeSO2-DDE by non-steroidogenic COS cells after transfection with a cDNA encoding P450c11. The interaction between xenobiotics and glucocorticoid synthesis should focus more attention to xenobiotic-induced hormonal disturbances.

Adrenocorticolytic DDT-metabolites: studies in mink, Mustela vison and otter, Lutra lutra.

The irreversible binding and toxicity of the DDT metabolites p,p′-DDD and o,p-DDD in the adrenal cortex of female mink Mustela vison were studied. Histological examination of adrenals from mink given a single i.p. injection of p,p′-DDD or o,p′-DDD (125 mg per kg body weight) showed vacuolation, necrosis and focal bleedings in the zonae fasciculata and reticularis. Autoradiograms of solvent-extracted tissue sections of minks given a single i.v. injection of p,p′-[14C]DDD (0.7 mg per kg body weight) revealed a high level of irreversibly bound radio-activity in the adrenal cortex. Microautoradiography showed that the irreversibly bound radio-activity was confined to the zonae fasciculata and reticularis. Incubation of p,p′-[14C]DDD and o,p′-[14C]DDD with mink or otter, Lutra lutra, adrenal homogenate (300 x g supernatant) resulted in an irreversible binding of radioactivity to protein from both species. The irreversible protein binding of the DDD isomers in mink and otter was decreased by addition of the cytochrome P450 inhibitors metyrapone and carbon monoxide, indicating a cytochrome P450 dependent metabolic activation. In contrast, 3-methylsulfonyl-[14C]DDE, a potent adrenocortical toxicant in mice, does not appear to be metabolized to a reactive metabolite in the adrenal cortex of mink or otter. In conclusion, both p,p′-DDD and o,p′-DDD are toxic to the mink adrenal zona fasciculata and reticularis following activation in situ to reactive, tissue-binding metabolites. The results suggest that p,p′-DDD and o,p′-DDD are adrenocortical toxicants also in otter. The involvement of environmental pollutants in the generation of the adrenocortical hyperplasia observed among Baltic seals is discussed.

Adrenocortical toxicity of 3-methylsulphonyl-DDE; 3: Studies in fetal and suckling mice.

Irreversible binding and toxicity of the DDT metabolite 3-methylsulphonyl-DDE (MeSO2-DDE) were examined in fetuses and suckling pups following administration to pregnant or lactating C57Bl mice. Tape-section autoradiography showed a high and tissue-specific accumulation and binding of MeSO2-DDE-14C-derived radioactivity in the late gestational fetal adrenal cortex. According to microautoradiography an irreversibly bound residue was confined to the zona fasciculata. Similarly, there was a high concentration of irreversibly bound 14C-labelled material in the adrenal zona fasciculata of suckling pups. Intraperitoneal injection of MeSO2-DDE-14C to lactating mice resulted in higher concentrations of radioactivity in the liver and stomach contents (milk) of the suckling pups than in the maternal liver. This treatment also resulted in a higher level of radioactivity in the adrenals of the pups than in the maternal adrenals, both at a subtoxic and at a toxic dose. Histopathologic examination of adrenals from suckling pups revealed extensive vacuolation and necrosis of the zona fasciculata 2 days following a single dose of MeSO2-DDE (25 mg/kg) to the dam. In the fetal adrenal zona fasciculata, slight degenerative changes were observed following a maternal dose of 50 mg/kg. In conclusion, the study shows that MeSO2-DDE is a highly tissue-specific toxicant to the fetal and postnatal adrenal zona fasciculata in mice. Based on the present data and on previous results in adult mice, we propose that a tissue-specific activation to a reactive metabolite in the fetal and postnatal adrenal cortex is mediated by cytochrome P-450 (11 beta).

Irreversible binding and adrenocorticolytic activity of the DDT metabolite 3-methylsulfonyl-DDE examined in tissue-slice culture.

The persistent adrenocorticolytic DDT metabolite 3-methylsulfonyl-DDE (MeSO(2)-DDE) was originally identified in Baltic grey seals, a population suffering from adrenocortical hyperplasia. In mice, MeSO(2)-DDE induces mitochondrial degeneration and cellular necrosis in the adrenal zona fasciculata. In this study, we used precision-cut tissue slice culture to examine local CYP11B1-catalyzed irreversible binding of MeSO(2)-DDE in the murine adrenal cortex. We also examined effects on steroid hormone secretion, histology, and ultrastructure. As determined by microautoradiography, selective binding occurred in zona fasciculata of slices exposed to MeSO(2)-[(14)C]-DDE. Quantification of binding by phosphorautoradiography revealed a 3-fold reduction of binding in slices co-exposed to the CYP11B1 inhibitor metyrapone. As measured by HPLC, corticosterone and 11-deoxycorticosterone secretion to the medium increased linearly for at least 24 hr. Addition of the ACTH analog tetracosactide caused an 8-fold increase in corticosterone secretion. Addition of metyrapone reduced corticosterone secretion 4-fold. Exposure of slices to MeSO(2)-DDE (50 microM) reduced the rate of corticosterone secretion by 90% after 24 hr of incubation. As determined by electron microscopy, vacuolated mitochondria were present in zona fasciculata of slices exposed to MeSO(2)-DDE (50 microM) for 24 hr. Our findings show that all effects of MeSO(2)-DDE previously reported in vivo could be reproduced in adrenal slice culture ex vivo. This test system allows analysis of zone-specific irreversible binding and effects on steroid hormone secretion and target cell ultrastructure. We propose adrenal slice culture as a simple ex vivo test system with which to examine the adrenocorticolytic activity of xenobiotics in human and wild animal tissue.

1,2‐dibromoethane and chloroform in the rainbow trout (Salmo Gairdneri): Studies on the distribution of nonvolatile and irreversibly bound metabolites

The disposition of metabolites from 14C-labeled 1,2-dibromoethane (DBE) and chloroform (CF) in juvenile rainbow trout was studied by autoradiography and quantitation of tissue radioactivity. Whole-body autoradiography of heated tissue sections showed a considerable level of nonvolatile metabolites of DBE and CF in the liver and certain areas of the body kidney. A lower level of metabolites appeared in the gills, intestinal mucosa, and olfactory rosettes in trouts exposed to DBE- or CF-containing water. Unlike previous studies in rodents, no specific uptake or binding of DBE or CF occurred in the surface epithelia of the upper alimentary tract. Microautoradiography and exhaustive tissue extraction confirmed a high irreversible binding of DBE metabolites in the liver and in a proximal tubular segment of the body kidney in fish exposed to DBE-containing water. A high level of radioactivity in the bile indicated fecal excretion of metabolites from both compounds. The results suggest that there is marked metabolism of DBE and CF in the liver and kidney, whereas the metabolism in the surface epithelia is low. The liver and kidney are proposed to be target organs of toxicity in fish.

Selective accumulation of chlorinated paraffins (C12 and C16) in the olfactory organ of rainbow trout

Abstract Three 14 C-labelled polychloroalkanes (C 12 and C 16 ), representing low (23% Cl by weight), medium (51%), and highly (68%) chlorinated paraffin (CP) mixtures, were presented to rainbow trout via the water. The uptake in fat-rich tissues was positively correlated to the degree of chlorination of the preparations. Notably, all preparations gave rise to a high and selective uptake of radioactivity in the olfactory organ and gills. This selective radiolabelling may reflect a general ability of these organs to enrich xenobiotics from the surrounding water. The olfactory organ may be a hitherto unforseen target for toxic environmental pollutants in fish.