Arsenic-A naturally occurring element that is often used in pesticides and herbicides. It can bioaccumulate to toxic levels, and is known to cause cancer in humans and other living things.
There is an extensive list of products that are exempt from registration including chilli, teatree and garlic oil, a number of copper-based products, derris dust, and even arsenic, but neem, seaweed extracts and milk aren't on this list.
When grown in arsenic-contaminated soils, it removes up to 10 ppm of arsenic in 2 to 4 months, accumulating the arsenic in its leaves. The fronds are then harvested and disposed of in a landfill.
Although leaching of arsenic into soil has been addressed, much outdoor lumber still contains copper and other chemical salts that are of concern in areas where small children play or vegetables are grown.
There is nothing that can be added to the soil to neutralize arsenic or convert it to something that is less toxic. Arsenic may be taken up by plants if the arsenic concentration in the soil is very high - greater than 100 ppm.
Your own organic fruit is not covered in arsenic (as some commercial apples are to lengthen shelf-life) or wax. Growing your own fruit means picking varieties for flavor, not looks or ability to travel.
Many bulbs are toxic because they naturally concentrate arsenic and other strong toxins in their roots.
They are treated with creosote, which is toxic to plants. Lumber treated with copper, chromium, and arsenic (CCA) is also not recommended for vegetable crops because some of the arsenic may leach out of the wood and be taken up by the plants.
Tim had built a retaining wall into the hillside to contain a vegetable garden, but when he finished, he noticed a sticker on the lumber that read "arsenic-laced.
Heavy metals-The heavy metals of concern to gardeners are lead, zinc, nickel, arsenic, copper, and cadmium. These metals can be toxic to plants (and a potential risk to humans) when they accumulate to high levels in the soil.
Raised beds are great for plants and for backs. When you build one, you want it to last. Conventional wisdom used to recommend using pressure treated lumber as a cost effective durable edging for raised beds. Then came the arsenic scare.
The Environmental Protection Agency (EPA) no longer allows a common treatment chemical, chromated copper arsenate (CCA), to be used to treat wood for most residential settings. Recent studies have linked the arsenic in treated wood to cancer.
However, compost has a very high amount of carbon, so if you add sawdust, add nitrogen (such as a cup of 10-10-10 fertilizer per 25 square feet). To be safe, avoid adding sawdust from lumber treated with CCA (chromated copper arsenic).
If you are just building a little greenhouse, consider building furniture that can fold up and be moved around or stored. Watch out for pressure treated lumbers, which are impregnated with highly toxic arsenic.
 See also: Plant, Water, Soil, Gardening, Wood
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