What kind of herbicide are we talking about? Most degrade and breakdown rather rapidly when exposed to air or sun or soil biology. And the persistent ones would not be affected by the charcoal anyway.

What you plan may be completely unnecessary........

I was told that it was a non-selective soil sterilant that goes into the soil to kill the root of undesirable weeds, etc.

We're going to need a name of the herbicide to determine what the impact and long-range effects are.

However, in...well, no case does charcoal ever do anything, really. Herbicides are going to wash in. Those that don't wash in, bind to the soil. They're not likely to have a greater tendency to bind to the charcoal and, even if they would, they won't bother due to having already found binding points that aren't in a proximate locale to the charcoal.

Chemically speaking, the rebinding has to be within femtometers for that to happen and charcoal doesn't go into solution, nor does a bound herbicide. There's no way for reasonable amounts to get that close.

Nor can you realistically add enough to overcome that.

It would be a really expensive way to slightly increase soil organic material, however.

There are some people in the organic gardening community that swear by activated charcoal. It seems the loudest ones own stores that also sell activated charcoal. I understand the theory, but I doubt it works as well in practice. Depending on what was used, it's probably already dissipated. If I inherited a yard like that, I would spray a quart of molasses to cover the yard (1/4 acre). If you have a farm and ranch coop nearby, you might be able to get molasses for 10 cents per pound in your own container. Mulch would help, but that's a lot of mulch. Organic fertilizer, like ordinary corn meal, applied at a rate of 10 to 15 pounds per 1,000 square feet would help revitalize the microbe community in the soil, and they can take care of your problem for you.

Plus precisely what do people think happens to said pesticides after they're bound? They magically go to Toledo on vacation? I kid, I kid, Ohio is a lovely state. Except Akron.

Pesticides that are already soil bound have no reason to be re-bound to simple carbon molecules. It's no different and not magical (and the carbon binding is generally not going to be any stronger, or make any difference, if it happens at all...which I doubt).

Pesicides that are soil-mobile are already on their way out and if the purpose is to dispel them from your soil, you might as well let them go away. The microbes who consider them lunch will take care of them.

It works if you eat a poison because it temporarily binds some of them until you vomit it up or defecate it out (don't try this with cyanide or anything else where adsorption would be ineffective...like alcohol). But that's a human with a nice, fast digestive system. Soils are not nearly the same thing although some of our processes are analogous.

And if one does use molasses, I'd recommend blackstrap for...well, unobvious reasons. It's a lot less processed and has more sulfur.

As an env. chemist with experience in toxic site remediation, I agree with morpheuspa. Chemicals (other than salts, i.e. most organic chemicals with limited solubility) will bind to soil organic matter, loosely or tightly depending on their structure. Some of them might bind more strongly to activated carbon. But the carbon isn't going anywhere, and it actually provides an excellent microporous surface for soil microbes to grow on. It will simply become incorporated into the soil matrix.

I would do some research on the specific chemical used, especially how fast it breaks down under normal conditions. Even the most persistent (the stuff that caused the toxic plant-killing compost) still goes away in two seasons.

Oh, by the way, what are your plans for this 1/4 acre? Lawn, gardens, ? Is it your primary concern that anything you plant may not survive?

As an armchair kitchen chemist who merely eats chemistry and biochemistry books as a hobby, I'm glad I got it right. :-) But long story short, I actually did sle...er, once once know an engineer who worked on toxic waste sites.

You got some of it by osmosis then. :-D

Okay you pros and semipros, what about generic, Bentonite, kitty litter for soil detox? I realize this is, perhaps, a change in scope for this topic, but it might be helpful to the OP, since we haven't confirmed his wishes as of yet.

Probably nyet. Again, it's not like the Bentonite is going to pick itself up and head down to the local EPA center to dispose of itself. The microbes are doing all they can in any soil.

In fact, highly oxygenated soils tend to be the most active. That would be sand and silt, not clay. Clogging up the soil with clay would, IMO, just slow crap down.

Now if you're just trying to keep it from dropping into the water table, maybe. It may bind to the clay (although there's no guarantee that any given clay has a high EC or that those EC points aren't already bound when you get the clay with something that has a higher binding energy than the pollutant).

So it also may not bind to the clay.

If you aren't an expert, and you don't know this clay personally and didn't see it grow up, you wouldn't know.

Don't get me started on the human concept of "detox" either. I can go on for effing days on the ineffectiveness of detox cleanses and detox diets. This is why you have working kidneys and a liver. If you do not, then you need a doctor, not a fad diet. Of course your urine became clear and you have diarrhea. You just flushed your system of all the water-soluble vitamins and most of the salts you need to live, which your renal system is filtering to keep in place. Great job there, Hunbot.

"You got some of it by osmosis then. :-D"

Pshaw. I picked it up in the gutter. And I'm proud of that fact.

"The Gutter. It's a night spot." -- Audrey, Little Shop of Horrors.

Since many herbicides are broken down by sunlight, perhaps tilling the surface a few times at long intervals will expose more of it to UV.

Some are, some are not, and I really hate being the Debbie Downer all the time. Penetrance of UV into the soil is really nil (it has trouble going through darker skin and Earth's atmosphere, after all).

Off the cuff, I seriously doubt that one could expose very much of the soil surface area as compared to the volume to UV when considering soil-binding herbicides (calculating penetrance at a generous 1/10th inch inverse logarithmic curve [and figuring it at more like half that] versus a one to six inch adsorption profile depending on the chemistry). When considering ones that wash through, there it's not a factor at all--they'd be gone long before you could even consider the idea.

That would be long before considering the issue of doing so in most gardens...much less lawns.

Now for chemicals left up top before washing in, that's another story. Even so, the result is simply a reduction in effectiveness over a period of time, and usually not a complete deactivation within any reasonable time period. And even there, filtering below the grass layer tends to protect those as well.

Figured. If my very pale skin can protect my lower dermal layers, opaque silicates wouldn't have any problem shielding lower layers.

Available evidence was the lack of bleaching when you turn soils and the fact that all earth tones have lightfastness ratings of I--and most of those have been proven in the real world to have lightfastness in sunlight of 50,000 years or more. I've watched an organic phthalo blue fade in a year in full sun (lightfastness I my fanny), while the siennas and ochres simply do not change.

Don't get me started on pigment durability.

Save it for the pigment durability forum. '-)

I'm already on those. And we've already had that discussion there where I've voiced my displeasure and been gently comforted by many, many others who are equally distressed.