Dioxin-like activity

Dioxin-like activity was assessed by the AhR recombinant yeast assay (AhR-RYA) performed as described in Noguerol et al. [79]. BP1, with an EC50 value of 0.61 mg/L showed tenfold more dioxin-like activity than BP3, with an EC50 value of 6.8 mg/L. However, two of their metabolites, 4HB and DHMB, presented 4 and 11 times higher activities, with EC50 values of 0.16 and 0.59 mg/L, respectively. No dioxin-like activity was observed for either 4DHB or THB. 

Dioxin-like activity during biodegradation processes of BP3, BP1 and 4-MBC by T. versicolor was below detection limits for all three compounds. These data indicate that metabolites produced by T. versicolor were in small amounts or rapidly metabolized in non-dioxin-like compounds. 

On the other hand, sludge samples showed a slight increase (two- to threefold) of dioxin-like activity after the fungal treatment, reaching values above the mg/L BNF equivalent mark. This data can be interpreted as an indicator for bio-activation of some compounds, other than UV filters, present in the sludge by the treatment with T. versicolor. These results emphasize the need of a broad screening of biological assays tests, as they differ in their capacity to detect specific hazardous effects. 

PCBs can move from local sediments into the avian food web, as judged by PCB accumulation rates of tree swallows (Tachycineta bicolor) from contaminated and reference sites (Custer et al. 1998). Patterns of relative concentrations of PCB congeners change from sediment to invertebrates, and from tree swallow eggs to nestlings (Froese et al. 1998). Dioxin-like activity (TEF) measured in tree swallow tissues could predict TEF in sediments and the reverse. Models of dioxin-like activity in the sediments of Saginaw Bay, Michigan, predicted that sediments were not harmful to tree swallows from that area (Froese et al. 1998). 

It is eoncluded that the determination of dioxin-like activity in cleaned sediment extracts using the DR-Luc bioassay has a consistent reproducibility, and can be used as a reliable and robust tool in the hazard assessment of dredged materials in a licensing system. Its advantage over ehemical analysis is that it also detects the effects of combined exposure as well as the effect of unidentified congeners or chemicals present in concentrations below the limit of detection of chemical analysis with a similar mode of action. In addition the use of cleaned sediment extracts circumvents the problem of disturbing sediment matrix effects. 

Sanctorum, H., Windal, 1., Hanot, V., Goeyens, L. and Baeyens, W. (2007). Dioxin and dioxin-like activity in sediments of the Belgian Coastal area (Southern North Sea). Archives of Env. Cont. and Tox., 52 317-325. 

Wong, H.L., Giesy, J.P., Siu, W.H.L., Lam, P.K.S., 2005. Estrogenic and dioxin-like activities and cytotoxicity of sediments and biota from Hong Kong mudflats. Arch. Environ. Contam. Toxicol. 48, 575-586. 

PCDTs were shown to be considerably less toxic than 2378-TeCDD and the most toxic PCDFs or PCBs. The compound 2378-TeCTA, the sulfur analogue of 2378-TeCDD, has been suggested to have dioxin-like activity Bioassays which detect the ability of 2378-TeCDD and related compounds to inhibit cell divisions in a mouse epithelial cell culture were used [8], In in vivo studies 2378-TeCTA has been shown to be less toxic than 2378-TeCDD [61]. 

Chlorinated naphthalenes (CN) are persistent environmental contaminants, which accumulate and biomagnify in human and wildlife food-chains. Many of the CN congeners show relatively high dioxin-like activity and have been identified as common food contaminants, especially in fish. 

Hilscherova, K., K. Kannan, Y.S. Kang, I. Holoubek, M. Machala, S. Masunaga, J. Nakanishi and J.P. Giesy. Characterization of dioxin-like activity of sediments from a Czech river basin. Environ. Toxicol. Chem. 20 2768-2777, 2001. 

Structure can be observed by the loss of dioxin-like activities of PCBs with ring substitution(s) at one or more of the ortho (2,2 6,6 -) position(s) which can lead to distortion from planar structure. Subsequent AhR binding data indicated that polychlorinated dibenzofuran congeners have binding activity similar to that of their dibenzo-p-dioxin counterparts (Woo and Lai 2003). 

Hexachloro (9H) xan-thene [38178-99-3] exhibited low to moderate toxicity in guinea pigs from a single oral dose of 12.5 mg/kg (DeCaprio et al. 1987). It may be noted that the absence of the second oxygen atom in the heterocyclic ring substantially reduced the dioxin-like activity. 

Fig. 6 TSP related toxicities PAH (sum of 28 substances) calculated dioxin-like toxicity (TEQ fg m ), genotoxicity Gen, reciprocal minimum genotoxic concentration, (MGC m ml ) ), dioxin-like activity AhR, 10 bioTEQ fg m ), antiestrogenicity AE, (IC25 m ml ) ), together with particulate matter mass (m, pg m ) and specific surface (5, 10 m g ) at sites in the Brno area, airport (rural), city (urban), Kyjov (urban), and Ivan (rural)...

Genotoxicity and AhR-mediated (i.e. dioxin-like) activity were found in aU size classes at all 4 sites in the Bmo area in similar magnitudes, i.e. the total suspended particulate matter (TSP) toxicity at rural sites was not lower than at urban sites (Fig. 6). Note, that also TSP mass and specific surface were not lower at rural sites. Activities were found in general highest in the small size ranges (Fig. 7). This... 

AhR-mediated activity results Dioxin-like activity is a useful marker of compounds that are able to activate the AhR receptor, which had been shown to be involved in numerous health effects such as impairment of immunity and nervous system or reproduction (Mukeijee 1998). There have been several studies describing AhR-mediated effects of the PMi (Wenger et al. 2009) and PMio (Clemons et al. 1998 Ciganek et al. 2004 Brown et al. 2005) aerosol size fractions. The TEQ calculated from the data of 28 PAHs (25 parent PAHs, retene, biphenyl and triphenylene) represents by average 7.5 and 95% of the dioxin-like activity associated with the particulate and gaseous fractions, respectively. Most of the activity could be produced by dioxins and furans, but also by partly oxygenated PAHs, such as polycyclic aromatic ketones and quinones that were also shown to activate AhR and to be produced by combustion pollution sources (Misaki et al. 2007). The results, furthermore, confirm that a significant portion of the AhR-mediated activity was produced by compounds present in the gas-phase at many polluted localities as it have been shown previously (Klein et al. 2006 Novak et al. 2009). 

Fig. 4 Estrogenic and dioxin-like activities in fractions of sediment extract from Kierikzee harbour fraction 2 showed characteristic ions of 17a- and 17 8-estradiol and estrone, and fraction 4 showed characteristic ions of various polycyclic aromatic hydrocarbons. Reproduced from [95]...

While both past and more recent human studies have focused on males, there are some limited data suggesting carcinogenic responses associated with dioxin exposure in females. Because both laboratory animal data and mechanistic inferences suggest that males and females may respond differently to dioxin-like activity, further data will be needed to address this question of differential response. 

PCBs can be divided into "dioxin-like PCBs" and "nondioxin-like PCBs." Congeners substituted in only the meta and para positions were approximate isostereomers of 2,3,7,8-tetrachlorodibenzo-p-dioxine (TCDD). Toxicological studies confirmed that these nonortho substituted "coplanar" PCBs bind to the Ah Receptor and induce a variety of in vitro and in vivo dioxin-like effects [74,132] and are classified as dioxine-like PCBs. All other PCBs thus fall into the nondioxin-like classification. Maximum dioxine-like activity is obtained for nonortho-PCBs when there is two or more meta, and both para positions are occupied [94,108]. Table 20.4 reports the toxicity of nonortho-PCB congeners expressed in terms of toxicity equivalent factor (TEF) [109,110,134]. TEF is calculated by comparing the toxicity of each congener with that of TCDD (TEF = 1). 

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