I was reading the thread on colored cardboard and it just brought up this more general question which I am still not sure I know the answer to. When soils contain something we are calling toxic then we can be certain it will at least disrupt the natural system in which the toxin is located But do such toxins actually find there way into the vegetables we eat? I could further refine the question in saying are toxins transmitted from soil through the structure of the plant to the fruit directly?, Or do they contaminate fruit (vegetables) threw dispersal from the adjacent soil to the fruit? My guess is that plants do not have their DNA damaged in a way that suddenly causes them to grow toxic vegetables, though at times this seems like the implication
I think a lot of the time, people underestimate Mother Nature and/or overestimate the power of chemicals to move through soil. For example, real-world experiments with gardens that were bordered with pressure treated wood show that there is an increased arsenic content the food if three conditions are met:
The food in question is a root vegetable (carrot, radish, potato, etc.),
The root grew within six inches of the treated lumber, and
The treated lumber was less than three years old.
If any one of these factors didn't exist, there was no appreciable fluctuation in the arsenic concentration within the produce. So, should you use arsenic-impregnated wood? I'd avoid it, but if it's all I have, I'd plant impatiens around the edges of my garden for three years (attracting pollinating insects - BONUS!) then proceed normally. But science be damned, you will always find someone willing to rip you apart for it.
“Life is entrusted to man as a treasure which must not be squandered, as a talent which must be used well.” ~ St. John Paul II
Fruit trees and plants that produce fruit(tomatoes, peppers, etc.) can be grown in lead contaminated soil. There is a membrane that prevents lead from getting in to the fruit. One caveat, the tree/plant itself should be considered toxic waste. Lead will also "sink down" in the soil over time(a very long time). It really depends what chemical(s) you're dealing with and what plants you want to grow.
As far as colored cardboard/paper goes, earth worms don't seem to be bothered by it(or can reproduce fast enough where I don't see an appreciable drop in population). I'd have to dig up parts of my garden in about a year to see if there is any microbial activity on the colored paper versus regular cardboard though. I recently reorientated my veg beds to take advantage of a contours, and all I found underneath were some plastic envelope windows and some tape that I failed to remove from a cardboard box that I used. This was only 8 months after I had put it all in at about 2" thick(which is why I moved up to 3" thick). I would assume from the observation that colored printed newspaper and glossy junk mail/catalogs/etc are indeed edible by microorganisms and that they keep a sufficient population to continue breaking it all down(just not plastic, but we already knew that). Since matter is neither created, nor destroyed(only changed), we can infer that any chemicals had to go somewhere unless they were changed by being consumed which is probably(not definitely) the case.
But I guess the big question is, was my food toxic? That I can't tell you unfortunately. Even in 20 years time, it might not have been toxic food that caused my death or whatnot. But I think the bigger question would be is it better to throw all of this stuff in a toxic dump or to release it in smaller amounts back in to the environment. I prefer the latter for absolutely no scientific reasoning other than lower p.p.b. are usually less deadly than higher concentrations.
As Mr. Watson said, "I think a lot of the time, people underestimate Mother Nature and/or overestimate the power of chemicals to move through soil."
It really depends on the 'toxin'. PCBs and similar definitely do end up in your food. Lead and arsenic very well might too (I think the 'membrane' idea is wishful thinking).
However, for things like PCBs and the stuff in cardboard a bit of biochar can take care of it. For lead and arsenic, those are chemical elements and cannot be broken down in any way (except by nuclear reaction). The only way to get metals off your land is to hyperaccumulate them and process the biomass to remove the lead.
I think it's a bit paranoid to avoid putting anything that might-could-possibly have any poisons into it into your dirt, but there are certainly things that it's best to avoid.
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