Eye On The Environment: County farm tries degradable plastic By David Goldstein Ventura County Star January 27, 2008

Consumer items made with degradable plastic have environmental costs and benefits.

On one hand, making an item out of cornstarch instead of petroleum seems like a great way to reduce the use of limited resources. On the other hand, many researchers conclude it takes more energy to make plant-based plastic than plastic from oil. Worse, degradable plastic is so unrecyclable that a small amount can make a large amount of conventional plastic unacceptable to recyclers.

This dilemma is especially difficult to solve because people use plastic for both disposable and durable items. For example, a plastic food package has a useful life of only a few minutes, and it can potentially affect the environment for decades if it becomes litter, so it might seem like a good candidate for degradable plastic. But a park bench made of recycled plastic has to withstand several seasons of direct sunlight and rough treatment, so it would have to be thrown away if it included degradable polymers.

Fortunately, the dilemma is easier to address when it involves agricultural film plastic, which Ventura County generates at a rate of about 10,000 tons per year. Degradable agricultural film plastic can be plowed back into fields, where it will degrade into soil.

One type of degradable agricultural crop cover is easily distinguished from recyclable film plastic. It is made of recycled paper, so it looks and feels very different from plastic. If pieces degrade prematurely and blow off into an adjacent field of plastic, or if sheets are accidentally collected with the plastic of an adjacent field, it can be easily distinguished and separated, avoiding contamination.

The Ventura County Integrated Waste Management Division formed a partnership with the McGrath Family Farm, CSU Chico and the UC Farm Advisor to conduct a pilot project on the two plastics last year. The test involved application of two kinds of degradable crop covers to rows of strawberry and tomato crops.

Using grant funds from the California Integrated Waste Management Board, the county staff obtained rolls of degradable plastic made of 60 percent potato starch and other rolls of crop cover made from recycled paper. The potato starch-based plastic, made in Washington state, had been used only in nursery applications, and the manufacturer was interested in adapting it for use on field crops. The paper-based crop cover was made in New Zealand and had been used for pilot projects there, but the manufacturer was eager to demonstrate it in the U.S. and continues to look for a location and backers to build a local factory.

After field and composting tests, Joe Greene of CSU Chico tested soil containing the degraded remnants of the two crop covers. Neither type significantly affected soil acidity (pH), both correlated to moderately increased soil moisture levels, and neither left a significant percent of solids in the soil. All of the soil samples passed CSU Chico's phytoxicity test.

The price of these alternative crop covers might be more than triple that of traditional plastic film, but composting crop covers would save topsoil and could reduce the time involved to remove crop covers.

Also, these alternative crop covers could reduce the use of fertilizers and pesticides because they can be custom-made for each farm, incorporating pesticides and fertilizers into the structure of the materials. For example, the potato starch-based plastic uses a three-layer film structure, and its manufacturer says it could incorporate into the inside layer an approved chemical that dehydrates pests. The pesticide would remain inactive until the surrounding material starts to degrade.

Similarly, the paper-based crop cover could incorporate a nitrogen-based fertilizer into its structure, countering the increase in carbon it would add to the soil when plowed under after its use.

The county Waste Management Division continues to assist a local company recycling standard agricultural film plastic in Camarillo.

The division also works with two collection centers that have been baling and exporting agricultural film plastic. Many loads pulled from fields have been too dirty for the local recycler, however, and export options have been limited by various factors. More options are needed to ensure the diversion of this material from landfills.

— David Goldstein is an environmental resource analyst for the county of Ventura. Representatives of government or nonprofit agencies that want to submit articles on environmental topics for this column should contact Goldstein at 658-4312 or david.goldstein@ventura.org