Interesting question, and I look forward to the discussion that will certainly ensue.

My understanding is that different toxic materials act differently. For example, lead in the soil tends to not be taken up much by the plants. However, bits of soil clinging to say, root crops like carrots, might be ingested and therefore it's recommended that root crops be peeled if soil is high in lead. That's what I've found through research, anyway.

Then there was someone who grew in a community garden who used to post a lot here a while back, and they were finding high levels of lead in their veggies -- even the tomatoes! (fruit crops are supposed to be fine when grown in high lead soil) So, unless she misunderstood the reports from her garden, or unless that particular community garden had extremely high lead levels, then there is something amiss in the information out there. I would think that getting a soil test and knowing your levels of heavy metals would be a starting point.

If children are eating the produce, then a tomato sprayed with pesticides, picked three weeks ago and shipped from Mexico is better than a tomato with a high level of lead in it grown organically and picked fresh from a community garden -- that's my opinion after researching blood lead levels and their effect on a child's brain development.

One opinion about one toxic substance. I don't know much about any of the other toxic stuff -- will check back to see where the discussion leads.

Elisa

Thanks, Elisa! I literally did not think of getting my soil tested during the growing season so I'll definitely do that.

Use raised beds filled with organic trucked-in soil.

Use raised beds filled with organic trucked-in soil.

But what about the chemicals leaching into the soil and onto the leaves of plants and such...also an important consideration, I think.

Most veggie plants don't take up excessive amounts of toxins...or much at all aside from extremely small trace amounts.

Nutrient exchange by plants rely on nutrient receptor points in plants and another layer of protection in the plant that selectively lets certain nutrients pass into root tissue.

Given that...most toxins don't make it in huge amounts into the plant, itself.

Also given that...because these toxins are taken up then excluded at the root zone (mostly through the casparian strip in the roots) there can be an accumulation of toxins in root crops.

That said, just being close to a road or urban area doesn't necessarily mean there's going to be toxins. Lead levels are higher in urban areas, though not usually extremely danger levels.

If one wants to be as safe as they can be...avoid growing root crops and wash anything harvested above ground. This is a bit overkill or not a concern for most, though.

There's not a huge amount of danger in urban gardening unless you're growing on soils you know have former industrial/dumping activity or some other toxicity issues.

A soil test, and then raised beds if the soil is a problem (as mentioned above) seems quite a responsible way to garden in cities where the soil is contaminated.

If there are toxins leaching and settling on leaves, then you're breathing the stuff in anyway, and most likely getting more of it than through the plants.

BTW, the garden where they were getting high lead levels in the tomatoes actually goes against what I have learned about uptake of lead by plants (as nc makes clear above.) The U of Mass soil test says that levels up to 500 ppm are fine to grow in (but not for children or pregnant women to work/play in). I suppose there are places with very high levels -- in the thousands ppm. -- and the only responsible way to garden there would be in raised beds.

A soil test may actually put your mind quite at ease. And should give recommendations according to what heavy metals you may have high levels of. Or you may be pleasantly surprised.

Either way, information is power, so find out what you're working with. And never worry while you're in the garden -- the plants hate worry. :)

A typical soil test is not going to check for chemicals that might be hazardous to you. Most test the soil's pH level, nutrient content and percentage of organic matter.

Usually the nutrient testing includes phosphorus, potassium, calcium, sulfur and magnesium. Most labs don't include nitrogen because the nitrogen content of your soil can change alot quickly.

Even micronutrients such as zinc, iron and copper are not usually included unless you request and pay for a more in depth analysis.

Do not assume that if some chemical is not reported that it is not there. It means it wasn't part of the testing.

Lead and other heavy metals would require specialized testing. So would various toxic chemicals from industrial waste, leaking storage tanks, etc. So if you are looking to find out about these, search for a lab that does more than a normal garden soil test and be prepared to pay a hefty premium.

University of Massachusettes lab tests for nutrients and heavy metals for $10.
They do not test for toxic chemicals, but the test also includes trace minerals like zinc, iron, copper, etc. and the heavy metals such as lead, cadmium and for aluminum, etc. It's the best test I've found, and very reasonable price.

This post was edited by elisa_Z5 on Sun, Jul 21, 13 at 8:17

This thread is leaning towards urban gardening but I have seen threads with people complaining about contamination in rural lands. Pesticide/Fungicide/Herbicide and fertiliser were used much more liberally post WWII. A lot of those chemicals are no longer allowed but still reside in soil currently farmed on.

If you have access to virgin soil, untouched by human activities you are very lucky. An urban plot may have better quality soil than an old farmstead, and vice versa of course.

should present no problem, as most of that fall out is probably not in a soluble form, if you use raised beds all the better. we are growing a tree barrier between us and unsealed road 70 meters away, this should block a lot of dust that will contain residuals from vehicles.

len

Here is a link that might be useful: lens bale garden