Posted by larryhoover on June 20, 2011, at 11:26:02
In reply to Re: dioxins and hormesis » larryhoover, posted by Questionmark on June 20, 2011, at 2:57:48
> Very interesting. But now i'm even more confused. So why all the concern about PCBs and dioxins?
There are a lot of factors at play. Some chemicals get a lot of attention, while others with more significant impact are ignored completely.
Remember Alar in apple juice? Alar is a chemical that was sprayed onto the apples early in the season so that they'd tend to ripen at the same time, making picking easier. It was detected in apple juice, and panic ensued. Nearly the entire crop year of apple juice was simply poured down the drain. And it was replaced by Chinese apple juice, that was never tested. But I did an analysis based on the concentration of Alar detected in the apple juice, and I determined that someone would have to drink 180,000 litres (over 40,000 gallons) of a/j per day, to reach an intake level that would potentially cause health concerns. If you drank 180 litres of apple juice, I bet the water content would kill you. Should they have banned water?
The whole environmental/pollution realm is a very political game. The "leaders" are driven by sound bites, and media exposure, to an alarming degree. I worked for the World Wildlife Fund in the '90s. They hired me to give the scientific lowdown on a number of chemicals of concern. And I worked very hard to determine what was known, what was suspected, and what needed to be determined about these chemicals. And then they ignored everything I found, because it was inconsistent with their policy at the time.
You may have heard about bisphenol A leaching out of polycarbonate plastics, once commonly used for water bottles. I did the full background work on that in 1997. It only took 12 or 13 years to make it to the public's attention. :-/
Sorry....I do get distracted. About PCBs and dioxins.....
Early work with rodents determined that some of these PCBs (there are around 200 different chemical structures under that umbrella) and a few of the dioxins were potent mutagens/carcinogens. Standard practise is to find the lowest dose at which the rodents appear to be affected, and then apply a 1000-fold reduction in that amount, as a sort of a safety factor. Well, when you do that for PCBs/dioxins, you're down in the low parts per billion, even parts per trillion range.
Another assumption is that the dose/response curve is linear. You start at zero dose/zero effect, and as you increase the dose, you tend to increase the effect. They worked backwards from that assumption, when they interpolated the human safe dose of TCDD/PCBs based on the rodent work. What we didn't know was that the dose/response curve is not linear.
In fact, with the dioxins and PCBs, what seems to happen is that as you move up from zero dose, the effect actually falls below zero (i.e. cancer rates fall, compared to unexposed people). I'm going to make an educated guess that our livers detect the trivial amounts that we are exposed to, and that protective enzymes are induced. And those enzymes protect us from other toxicants in our diets or environment. (Broccoli contains a carcinogen. You just never know what will get you.) Anyway, at some undefined higher dose, dixoins/PCBs will begin to act as carcinogens, and the dose/response curve will rise above zero (that's what is meant by hormesis.....inverse response depending on dose range). Based on the link I provided, those at the higher exposures of PCBs/dioxins were still not at the undefined level.
> And what about heavy metals?
Oh, we're much clearer on those. You do need to manage your heavy metal exposure. But, few doctors will tell you that selenium is protective against mercury.
> ... Aughhhhh. I swear, sometimes, w health, and politics, and damn near everything, the absolute truth just seems unattainable.It's so true. Remember butter bad/margarine good? I had some very serious arguments about that one, early on. Steady yourself, but red meat just got a clean bill of health. (I have had some serious arguments about that, too. Being ahead of the curve is sometimes a challenge, but I am a stubborn lad.)
Lar
poster:larryhoover
thread:904699
URL: http://www.dr-bob.org/babble/20110619/msgs/988873.html