SYNERGY: of DIOXINS

What are the combined effects of the dioxin family?

Unless it can be shown otherwise we must assume that dioxins, furans, PCBs and others will add together to give a total dioxin-like toxicity. 

This has been shown experimentally for dioxins and furans (Eadon, 1986), but doubts have been expressed about the validity of adding the PCBs' contribution in the same way (Goldstein & Safe, 1989). Studies have been carried out that show PCBs acting against and reducing TCDD effects. 

However, a moderately toxic PCB, which produced only mild pre-birth effects in mice on its own, was found to increase TCDD effects in those mice tenfold (Birnbaum et al., 1985).

In addition: 

PCBs are a mixture of dioxin-like and non-dioxin-like molecules. Some bind strongly to the Ah receptor and others only weakly. 

PCBs have been reported to exert other effects separately from their action through the Ah receptor: for example there are effects on nerve signal transmission linked to a PCB which binds only weakly to the Ah receptor (Seegal et al., 1990).

Certain PCBs can increase the levels of the Ah receptor in the liver, and hence increase susceptibility to low doses of other dioxin-like compounds(Goldstein & Safe, 1989). 

However, laboratory investigations of interactions such as these cannot possibly cover all that are possible in humans and animals exposed in the environment to the whole range of dioxin-like compounds. 

Considering both the evidence for enhancement and lessening of effects, we have to assume that the different compounds add together to produce a total dioxin-like toxicity, which can be estimated by using the TEFs given earlier. 

In other words, dioxins plus PCBs equals more dioxins.

ORIGINAL SOURCE

Nov 2006 STUDIES - BINARY MIXTURE OF DIOXINS: PCB

3,3N,4,4N,5-PENTACHLOROBIPHENYL 
(PCB 126)
(CAS NO. 57465-28-8)



AND

2,3N,4,4N,5-PENTACHLOROBIPHENYL 
(PCB 118)
(CAS NO. 31508-00-6)


Results 

Female rats administered the mixtures of PCB 126 and PCB 118 developed a variety of diseases in several organs, including cancers of the liver, lung, and mouth.  

A variety of other toxic lesions observed in exposed animals included 

hypertrophy
hyperplasia
hepatopathy
fibrosis, and necrosis of the liver
hyperplasia of the oral mucosa
metaplasia of the lung
atrophy of the thymus
hypertrophy of the thyroid gland
atrophy of the adrenal cortex
vacuolization and atrophy of the pancreas
kidney nephropathy
hyperplasia of the nose
hyperplasia of the forestomach
hemorrhage of lymph nodes and brain
atrophy of the spleen. 

Conclusions 
We conclude that the mixtures of PCB 126 and PCB 118 caused cancer and other toxic effects at several sites in female rats.

Study Results 
niehs.nih.gov: Paper published

Dioxin! The Facts

Dioxin! 
What Citizens, Workers and Policymakers Should Know.





Linda Birnbaum, who is currently the director of the National Institute of Environmental Health Sciences discusses what dioxin is, how toxic it is, and whether it causes cancer.

Although the interview was conducted in 2004 when Dr. Birnbaum  was head of the EPA  Division of Toxicology, we believe it continues to provide a useful and easy to understand summary of some of the available evidence against dioxin.

The video was originally commissioned in 2004 by the Ecology Center of Ann Arbor and the Public Interest Research Group In Michigan, but has never been released publicly until today. Thanks to the Ecology Center and Dr. Birnbaum for agreeing to make this public.