Important: When setting up and maintaining your garden it is important to take care to avoid products that may cause harm to the health of your garden and students.
CCA treated timber (treated pine)
Timber treated with copper, chromium and arsenic as a preservative has been phased out for all domestic use in the United States, European Union (EU), Canada, Indonesia and Vietnam, and restrictions placed on its uses in Japan.
The Australian Pesticides and Veterinary Medicines Authority (APVMA) conducted a review of CCA treated timbers and, in March 2005, declared this preservative to be a restricted chemical product (RCP) in the public interest.
The review states that the APVMA "were not satisfied that the continuing use of CCA for timber used in structures with which the public (and particularly children) are likely to come into frequent and intimate contact is safe", and APVMA regulations that restrict the uses of CCA treated timbers came into effect at the end of March 2006.
Included in the APVMA regulations is (10.1. iv): "not permitting uses of CCA timber treatment products for timber intended for use as garden furniture, picnic tables, exterior seating, children’s play equipment, patio and domestic decking, and handrails".
Common sense would dictate that the APVMA restrictions would also apply to school garden beds (as they do to sand pits) because these timbers can leach arsenic (a known carcinogen) onto the timber surface and into compost and soil for up to 20 years, and that there are a number of factors that increase the amount of arsenic leached from treated timbers, including high UV light levels.
The APVMA regulations do allow the use of CCA treated timber for 'structural timbers' and the timber industry has included retaining walls in that description. However, the APVMA Review (page 11) clearly states, structural timbers "where frequent contact is unlikely, and the level of exposure and risk, is low". For more information see:
Alternative timber preservation methods are available. However, some contain pesticides that are developmental neurotoxins, and others leach copper or boron – some plants and soil organisms are sensitive to excess amounts of these trace elements. Consequently, we do not recommend the use of preserved timber as edging for garden beds in schools. Suitable edgings are suggested in the 'Garden Beds' section of 'Introduction 2: Getting Down To Earth'.
For other structures in school gardens, timbers preserved with alkaline copper quaternary (ACQ) appear to be the most readily available. Unfortunately, ACQ timbers also have a green tint, which weathers over time to a honey brown. As the labels on CCA treated timbers are affixed with a single staple and easily dislodged, the onus is on the consumer to ensure before purchase that the timbers are preserved with ACQ, not CCA.
For more information on products containing alternative methods of timber preservation, see:
Carpet and carpet underlays
Natural fibres are treated with persistent pesticides before sale, and many carpets contain toxic chemicals as stain or flame repellents. Some felt underlays were made from asbestos-contaminated hessian. When exposed to the elements, chemicals from these products can leach into beds, compost and worm farms if used as covers or to suppress weeds.
Phospho-gypsum or by-product gypsum
Phospho-gypsum is a by-product of synthetic phosphate fertiliser manufacture. It can contain high levels of cadmium, which is harmful to human health and not suitable for organic gardening. Please check before purchase that the packaging has an organic-allowed label (see below) or the label clearly states that the product is natural or mined gypsum. (See EOG&MP pp 37-8)
Old car tyres
Car tyres can leach cadmium and other heavy metals into soil as they weather, and should never be used for garden or compost containers. Plenty of well-made, mature compost in garden beds can limit cadmium uptake. However, cadmium uptake by plants is increased in acidic soils; soils containing immature compost or uncomposted manures, or where water is high in chlorine. (See EOG&MP p 27)
Uncomposted manures and mulch cut from pastures sprayed with broadleaf weed killers
The Australian Pesticides and Veterinary Medicines Authority (APVMA) has registered more than 200 pyridine herbicides that are designed to kill broad-leafed plants while leaving pasture grasses unaffected. Pyridine herbicides include those containing aminopyralid, clopyralid, picloram, fluroxypyr or triclopyr, or combinations of these.
The problem with these poisons is that the herbicide remains active in mulch cut from sprayed pastures and in manure from animals that have grazed on sprayed pastures until the chemicals are broken down by microbes. Aerobic microorganisms produce the fastest breakdown (see Lesson 3 of this program). And, as the APVMA regards the person who sprays the herbicide to be the 'end user of the product', the APVMA is not required to warn the public that adding affected manures or mulches to garden beds can damage plant growth for up to 24 months.
Tomato, potato, capsicum, chilli, eggplant, lettuce, sunflower, beetroot, silver beet, spinach, carrot, parsnip, parsley, strawberry and all legume plants are particularly susceptible to damage from these herbicides. The pyridine herbicides most likely to cause damage are those containing the persistent aminopyralid (2 registered products), clopyralid (62 registered products), and picloram (60 registered products).
To prevent pyridine herbicide damage:
• Use only aerobically composted manures on gardens. Aerobic composting requires weekly turning or stirring to ensure the composting process is carried out by microbes that require oxygen. Ideally, as the composting process begins, the internal temperature of the compost heap should reach 60 degrees Celsius. Breakdown of these herbicides will be extremely slow in compost heaps that are not well aerated.
• Mulch registered for use in organic farming and gardening (e.g. BFA registered input) does NOT contain any herbicides and is safe to use. Mulches from unregistered sources are high-risk products because the materials are dried and baled, which prevents aerobic microbe activity, and the herbicide remains active.
• If you are unable to purchase registered manures or mulches, and your supplier is unable to confirm that the products are from herbicide-free paddocks, test the safety of the product by sowing some seasonally suitable peas or beans in pots containing registered potting mix with the uncomposted manure mixed through it, or covered with the purchased mulch. Keep the test pots well fed and watered to eliminate other sources of plant stress.
Symptoms of damage to look for are:
Poor germination or death of seedlings, twisted, cupped, elongated, or fern-like leaves and twisted growth, and misshapen pods.
If you find that manure is affected, take care to ensure good aeration during composting. If mulch has been affected, use it on beds that you can leave fallow until aerobic microbes in topsoil break down the herbicide or, if space is limited, compost it aerobically. Notify your supplier and the APVMA of the problem with the product.
The only safe compost to purchase is compost registered for use in organic farming or gardening. The most common symbol indicating this is the BFA “Bud” registration mark.
You can find Australian product names of these herbicides by going to the APVMA's Public information (PUBCRIS) page. Under product type select 'HERBICIDE', then type aminopyralid, clopyralid or picloram in the active constituent panel. Click 'Search'.
You can find BFA registered inputs at the link:http://www.bfa.com.au/PrimaryProducers/OrganicFarmingInputs.aspx
Plastics with recycling codes 3 and 7
Recycling code 3 is for polyvinyl chloride (PVC) products (including old plastic shower curtains) that leach toxic chemicals. Recycling code 7 covers polycarbonate and resin products that may leach Bisphenol A (BPA) when exposed to heat.
Herbicides should not be used to clear the garden area of weeds or other vegetation (or at any other time) These products kill, or inhibit, a range of soil organisms, and increase the incidence of soil-borne diseases. They can also cause allergic reactions in humans, especially children. These products will counteract your efforts to produce healthy, organic soil.