There are many reasons not to use treated wood for your fences and/or retaining walls. The chemicals most used to preserve wood---creosote (on railroad ties, among other things) and penta---were banned by the EPA in 1986 for indoor use and for many outdoor uses. The chemical used to pre-treat wood (CCA, a mixture of copper, chromium, and arsenic called chromated copper arsenate) has been shown to leach into the soil and to transfer to human skin through contact.

There are safe paints and preservatives for coating wood; there are safe types of pre-treated wood; some people use stone, cement blocks, or other materials instead of wood.

Below is lots of info about treated wood and alternatives.

Start with the page on the EPA site, which is full of info on treated wood. It includes a section on alternatives and some questions and answers about studies...look under Sealant Studies (Coatings).

If you find this too technical, try the next two links below.
The Natural Handyman website has good information

Washington Toxics Coalition has a page about safe and unsafe paints and wood preservatives. Lots of background info on the toxicity of treated wood is included as well.

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Date 2006-12-08
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The Material Safety Data Sheet for Sluggo indicates that one should avoid disposal of this product near bodies of water (see Section 13), though there is not definitive information in Section 12 on the ecological impacts of the product on algae and other life forms. Here is a link to the PDF document.

See also pages 20 and 21 of the document "Grow Smart."

It does not list Sluggo, Escar-go, or any of the other iron phosphate products as water pollution hazards, but the MSDS sheet makes me think there is a potential problem with dumping large quantities. It seems not enough information is out there, perhaps because the research has not been done. Here is the page from the Pesticide Action Network database, where you can see that iron phosphate's eco-toxicity has not been established.

Here is what the Environmental Protection Agency has to say about iron phosphate slug baits:

Ecological Effects Hazard Assessment

"A number of ecological effects toxicology data requirements were waived based on the known lack of toxicity of iron phosphate to birds, fish and non-target insects, its low solubility in water, conversion to less soluble form in the environment (soil), and its use pattern (soil application). An acute oral toxicity study in Bobwhite quail (NOEL & LD50 greater than 2000 mg/kg) indicated that iron phosphate was practically nontoxic to avian species. Based on these factors, the data requirements for the toxicity studies in Mallard duck, rainbow trout, freshwater invertebrates, and non-target insect/honeybees are waived. It is likely that there will be exposure to ground-feeding non-target insects and earthworms. Submitted studies involving ground beetles, rove beetles and earthworms demonstrated that the product will not affect these organisms at up to two times the maximum application rate.

Environmental Fate and Ground Water Data

Exposure assessments on this type of product (biochemical pesticide) are not performed unless human health or ecological effects issues arise in the toxicity studies for either of these disciplines. Since no endpoints of concern were identified, there is no requirement for environmental fate data.

Ecological Exposure and Risk Characterization

Exposure to daphnids and other aquatic invertebrates would not occur based on current label use directions. Exposure to honeybees is also not expected to occur, due to the composition and particle size of the end-use product and its use pattern (soil application). Non-target insects, such as ground beetles and earthworms, could encounter the end-use product; however, in tests of rove beetles, ground beetles and earthworms, no effects were observed at up to twice the maximum application rate. Thus, the acute risk to aquatic invertebrates, non-target insects, and earthworms is considered minimal to nonexistent."

University of Maryland Extension has information on the impact of Phosphorus on aquatic life, a process called eutrophication. However, the iron phosphate in Sluggo and similar products binds with Phosphorus, which may mitigate the effects in water.

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Date 2008-02-07
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Do you know which weed and feed product was used? That would help in determining the chemical's half life (persistence) in the soil. Regardless of which chemical was used, my recommendation would be not to plant any edibles in a site which has been treated with weed and feed, but to find another location for your food plants (such as containers made of safe materials, or raised beds with a barrier between the bed and the chemically treated area of the garden).

Local garden writer Ann Lovejoy has discussed weed-and-feed products in her column. Here is a link.

Here is what retired Washington State University Extension agent Mary Robson had to say on this subject in one of her columns:

Just one note of caution-be careful with all chemicals. Many pesticides ordinarily used in gardens are not allowed on edibles. An example is Lawn Weed and Feed which will harm any broadleaf plant whether lettuce or marigold or petunia. It's probably safest to keep pesticides out of the garden if you plan to eat the produce.

From Washington Toxics Coalition:

The Hazards of Weed and Feed

Weed and feed is a mixture of lawn fertilizer with weed killer, usually 2,4-D and related compounds. The problem with weed and feed is that it is designed to be applied to the entire lawn regardless of whether or not weeds are actually present. This encourages over use. For example, if 30% of your lawn is covered in weeds, 70% of a weed and feed application will be wasted, since the herbicides have no residual action. Since many people do not realize that weed and feed is a pesticide, they may be less inclined to read an follow label instructions. For example, did you know that it is illegal to apply weed and feed more than twice per year on the same site?

The herbicides in most weed and feed products are mobile in soils and are widely found as pollutants in local streams, according to the U.S. Geological Survey. In addition, 2,4-D is neurotoxic and may be a carcinogen according to some studies.

Weed control should be practiced only as needed, not every time you fertilize. Mechanical controls are preferable to protect health and the environment. If chemical controls are used, spot treatment should be utilized to minimize product use and resultant risks from direct exposure and track-in to the home on shoes and feet.

Here are links to information on some common weed-and-feed type products and their hazards:

From the Pesticide Action Network North America

From the Journal of Pesticide Reform

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Date 2008-02-07
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