Compost made from yard waste will contain some pesticide residues but very likely at miniscule levels. Sources of these residues include any treated materials that went in as feedstock as well as background levels of persistent pesticides that are found everywhere in the environment. In general, the commercial composting process is quite good at breaking down the modern pesticides that are used on landscapes today, so levels in the finished compost should be much lower than in the feedstock materials. One important exception is clopyralid, an herbicide that has been shown to survive the composting process in sufficient amounts to damage some susceptible seedlings grown in contaminated compost. Some states, including Washington and California, have already taken action to restrict the use of clopyralid so that contaminated material cannot enter commercial composting facilities. For more information on clopyralid, go to this Seattle Public Utilities web page.

Generally, you do not need to be concerned about pesticide residues in municipal compost made from yard waste. The benefits of using compost far exceed any risks. If you have any concerns, you should contact your supplier or producer and ask for test results.

Metals in Municipal Yard-Waste Compost

Municipal compost made from yard waste will contain background levels of metals that are generally present in the soil, but normally the amounts found in compost should not be of concern. These metals enter the compost process via soil attached to the root balls of plants, in dust on foliage, and in the plant material itself. Metals are elements and so cannot be broken down by chemical or biological processes. A variety of metals are found naturally in soil, but in urban areas and contaminated sites soil concentrations of some metals can be much higher than normal. The metals that are usually of greatest concern are lead, cadmium, arsenic, and mercury because these are the most toxic. Of these, lead levels are likely to pose the greatest risk to human health except in unusual circumstances. Lead levels in urban environments tend to be elevated because of its previous use in paint and in gasoline.

Standards have been set in some states for maximum allowed levels of certain metals in compost. In Washington state, lead levels in compost must be 150 parts per million or less for compost with unrestricted uses. If you have questions about a particular product and how metals compare to standards, contact your supplier or producer.

Biosolids Compost

Yard waste compost is made from collected plant material. Biosolids compost (e.g. GroCo, TaGro, Milorganite) is made from sewage sludge, usually composted with sawdust. In general, compost made from biosolids is more likely to present risks to users because the feedstock material is more hazardous. In particular, it is more likely to contain pathogens, pharmaceutical residues, and organic contaminants from industrial and household product wastes. Like yard waste, it also contains metals.

Biosolids are regulated by the U.S. Environmental Protection Agency, which sets limits on certain metals and organic compounds, but many compounds are not monitored. Levels of contaminants in actual products will vary depending on the sources and treatment processes in place.

While in principle we support recycling of organic wastes, for home landscape use we have a preference for compost made from yard waste over that made from biosolids. However, individuals can obtain information from compost producers and make their own decisions.

Safe Use of Manure

There is some potential risk from the use of fresh manure on vegetable gardens, although it is fairly small and can be managed through appropriate techniques. Cat, dog, or pig manure should not be used because of potential parasites. Well composted manures are much less likely to contain dangerous pathogens.

The following additional tips are suggested by Van Bobbit and Dr. Val Hillers of Washington State University (view complete article on this WSU website):

Apply fresh manure at least 60 days before harvesting of any garden vegetables which will be eaten without cooking. If you apply manure within 60 days of harvest, use only aged or composted manure.
Never apply fresh manure after the garden is planted.
Thoroughly wash raw vegetables before eating.
People who are especially susceptible to foodborne illnesses should avoid eating uncooked vegetables from manured gardens. Those who face special risks from foodborne illness include pregnant women, very young children, and persons with chronic diseases, such as cancer, kidney failure, liver disease, diabetes or AIDS.

Bone Meal and Mad Cow Disease

Theoretically it’s possible for bone meal to spread mad cow disease, since the restriction against “downer” cattle that applies to meat does not apply to animal parts used in bone meal. However, so far it has not been known to happen. The prion protein that is thought to cause bovine spongiform encephalopathy (BSE) has not been found in blood, bone, or muscle, only in the brain, spinal cord, and small intestine of cattle.

If you are concerned about the potential risk, you can do two things: wear a mask to reduce the risk, or use fish bone meal instead.

Newspapers for Compost or Sheet Composting

Newspaper is often recommended as bedding material for worm bins and as a base layer for sheet composting over grass. The concerns about its safety are related to the inks.

Inks contain a solvent and various pigments. The solvents evaporate fairly quickly after printing and shouldn’t be an issue by the time the paper is used in composting. The pigments, as you can easily see, are still there. Pigments that used to be used in newspaper printing contained toxic metals.

The general consensus seems to be that inks used today in newspapers are much less likely to contain metals, and many are vegetable based. Many sources remain wary of colored inks, especially those used on glossy advertising inserts. To be perfectly safe, we would suggest stripping out any advertising inserts and only using the parts of the paper that are printed locally. If you want to be absolutely sure, you can call your local newspaper and ask about their inks.

Lawn Fertilizers

Avoid “weed and feed” or any mixture of fertilizer with an herbicide or other pesticide. Such pesticide mixtures encourage overuse and inappropriate use of pesticides. (For more on weed and feed, see the next FastFacts.) Also avoid lawn fertilizers with a high percentage of water-soluble nutrients. They are more likely than organic or slow-release fertilizers to be a source of water pollution.

Choose a high quality organic fertilizer with a balance of nutrients appropriate for your soil. For example, in Western Washington, WSU Cooperative Extension recommends lawn fertilizers with NPK (nitrogen, phosphorus, potassium) in a ratio of 3-1-2. This could include 3-1-2, 6-2-4, 9-3-6, and so on. Consult local cooperative extension agencies for a recommendation in your area. You may also want to get a soil test to determine better what your soil conditions are and whether adding lime would be beneficial to adjust the soil pH. Soil tests are available through the University of Massachusetts.

Phosphorus is a serious pollutant of lakes in certain locations and its use may be regulated or discouraged. If that is the case in your area, look for low-phosphorus or phosphorus-free fertilizers.

For more information on fertilizers, see our fact sheet, Choosing Fertilizers for the Lawn and Garden (35kb PDF file).

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.

Coated Fertilizers versus Organic Fertilizers

Coated fertilizers are made with pellets that have a shell on the outside to control the release of nutrients. The fertilizer itself can be, and usually is, synthetic in nature. Organic fertilizers, on the other hand, are made of naturally occurring plant, animal, or mineral-based materials. Most organic fertilizers release their nutrients slowly, although some types of fish fertilizer are relatively water soluble. The choice may involve philosophical principles as well as good gardening practice. Either coated or organic fertilizers will provide slow, steady nutrients, but the nutrients in the organic fertilizer may be more likely to require bacterial action to release them, while the shell coating only needs water and heat. Using an organic fertilizer, then, helps to support the beneficial microbes that you want in your lawn or garden. In addition, organic fertilizers are usually made from renewable resources and do not contain materials manufactured from petroleum.

Lead and Arsenic Levels in Fertilizers

Metals concentrations in all fertilizers sold in Washington state can be found on the Washington State Department of Agriculture’s website. But what do these numbers mean to you? One way to think about it is to say that non-nutrient metals levels (like lead, cadmium, arsenic, and mercury) in fertilizer applied to landscapes should not be higher than the background levels in the soil. If this were true, levels in the soil would not be increased by use of the fertilizer and would thus not build up over time. Background soil levels vary widely with location and may be found on various websites.

Many fertilizers have metals levels far below soil background, and metals in “organic” fertilizers made from plant, animal, or mineral material are sometimes somewhat higher than those in synthetic fertilizers. How do you choose from them the most appropriate fertilizer for your needs? This is an important question because choosing the fertilizer with the lowest levels of all metals isn’t necessarily the best choice.

In general, choose fertilizers intended or suitable for your use and with an appropriate amount and balance of nutrients. For landscape uses, those with a minimum of water-soluble nutrients are less likely to be a source of water pollution. Organic or slow-release fertilizers are the best choice. Synthetic, water-soluble fertilizers are fine for container plants. For more information on fertilizers, see our fact sheet Choosing Fertilizers for the Lawn and Garden (35kb PDF file).

Testing Garden Soil

The University of Massachusetts at Amherst Department of Plant and Soil Sciences offers soil testing to anyone by mail. For pricing and instructions, see their website. A typical soil test for pH, nutrients, and extractable metals costs only $9.00 and comes with a report that explains the results. For $13.00, you get all the above plus an analysis of organic matter. These are bargain prices.

Many universities offer soil tests. Check with one near you. You can also investigate commercial laboratories locally or on the Internet.

Lead and Arsenic in Garden Soil

The levels of lead and arsenic in your soil that can be considered safe depends on how you use your land, what groundcovers are present, whether you have young children, and many other factors. You will find different levels in different parts of your yard because the distribution of metals is not constant, especially if the sources are not of natural origin. For example, lead levels are likely to be much higher near the foundation of an older home than in mid-yard.

There are some guidelines we can use to put your lead and arsenic levels into perspective. At the low end, the natural average background levels of lead and arsenic in the earth provide a baseline. You are unlikely to be able to get below these levels and they should not present much risk. At the high end, the U.S. EPA and states have established cleanup levels for these metals. The cleanup level is the concentration to which a contaminated site must be cleaned up to no longer be considered contaminated. While the residential cleanup level is supposed to be safe, it certainly represents the upper end of what is acceptable near a home. Here are the applicable numbers for lead and arsenic (units are parts per million):

Average Background

WA Residential Cleanup Level

Arsenic

7ppm

20ppm

Lead

17ppm

250ppm

So, if your levels are closer to background than cleanup levels, you shouldn’t worry. If they are near the cleanup levels, you might try to understand why and be somewhat more concerned. If you tests exceed cleanup levels, you should talk to your health department about risk reduction measures you and your family can take.

Vermiculite in Potting Soil

Vermiculite is a naturally occurring mineral material that is sold both by itself and as a component in potting soils. Certain kinds of vermiculite contain tiny asbestos fibers that can cause lung disease, including cancer, through inhalation. It is impossible at this point to know which products contain these fibers. Risk to the casual gardener is probably small but naturally increases with frequency of use. Asbestos risk is greatly increased by smoking tobacco products.

Some general safety tips for working with all potting materials can greatly reduce your risk from asbestos. Always wear a dust mask when working with dusty gardening materials such as granular fertilizers, bone meal, rock dusts, potting soils, and vermiculite. When using packaged potting soils, mist the material lightly with a water spray to reduce dust. If you really want to avoid any chance at all of inhaling asbestos from gardening materials, avoid using vermiculite or potting soils containing it.

Insecticides in Potting Soil

Potting soils containing an insecticide such as imidacloprid are now available. The idea is apparently that the plants take up the insecticide from the soil and thus become “immune” to insect attack. We oppose these insecticidal potting soils for the same reasons that we oppose all mixtures of pesticides with other materials such as fertilizers. Such products encourage overuse of pesticides because they allow no flexibility based on whether the pesticide is actually needed in a given situation. The need for pesticides on seedlings or potted plants depends on the variety of plant, the location, and the care the plant is given. If the plant is healthy and well cared for, an insecticide should rarely be called for. One size does not fit all. There is also the waste issue. Potting soil containing insecticide is likely to be considered a hazardous waste by local governments, but because it looks like ordinary potting soil it may not be recognized as a pesticide. We view the incorporation of insecticides into potting soil as a bad idea and not one that we think gardeners should support.

Washington Toxics Coalition

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