New Films Enhance Plant Growth But May Leave Chemical Residues in Soil

Pamela Coleman
Farm Policy Analyst

Farmers recognize the advantages of plastic mulches: thin sheets of black plastic warm the soil, enhance crop growth, and suppress weeds. Although these are commonly used by many farmers, they are non-biodegradable, so they must be removed and discarded at the end of each growing season.

At their Fall 2012 meeting, the National Organic Standards Board (NOSB) voted to approve the addition of a new kind of “biodegradable” plastic mulch, one that would not need to be removed from the fields. The proposal to approve this material elicited many comments, both for and against.

A truly sustainable alternative to petrochemical-based plastic—which generally ends up in a landfill—would be welcomed by The Cornucopia Institute and by many farmers. Why, then, did Cornucopia and other public interest groups ask the NOSB to postpone approval of this material until further research could be done?

The Story

The story began when the Biodegradable Products Institute, a trade/lobby group that represents manufacturers of biodegradable films, submitted a petition to the USDA National Organic Program (NOP) on March 23, 2012. The petition requested that organic farmers be allowed to use biodegradable/ bioplastic/ biobased mulch films without removing them at the end of the growing season. There are several brands of bioplastic films currently being produced, including NatureWorks PLA INGEO^TM, Mirel^TM, BioTelo, Ecoflex^TM, Eastar Bio^TM, and MaterBi®. More are being developed.

These materials are called bioplastics, because they are biobased rather than petroleum-based, and they meet the chemical definition of a plastic. Biobased plastics are made primarily from plant materials, such as corn starch, although synthetic compounds may be added during manufacture. Biodegradable is defined by international standards, but essentially it means that the film breaks down so that pieces of it are not visible.

The NOP reviewed the petition and forwarded it to the NOSB crops subcommittee, along with a report by a third-party expert, called a Technical Evaluation Report (TER). After reviewing the petition (299 pages with appendices) and the TER (22 pages), the crops subcommittee recommended that synthetic bioplastic films be allowed in crop production. This recommendation was voted on and approved by the full NOSB at the Fall 2012 meeting.

Are These Mulches Really Biodegradable?

Cornucopia is concerned that an overly broad category of synthetic substances is being added to the National List. Although the mulches were petitioned as a group, they are unique, each using a different manufacturing process and different raw materials. Polylactic acid (PLA) mulch consists of plant starches fermented by bacteria. Polyhydroxyalkanoate (PHA) mulch is produced via chemical synthesis, bacterial fermentation, or transgenic cells. The aliphatic-aromatic copolymer (AAC) mulches are manufactured by chemical synthesis.

While some of these may be appropriate for organic crop production, others may not be. We urged the NOSB to request separate petitions for each type of plastic film, and to delay the vote until each type can be individually reviewed and voted upon.

Furthermore, we were particularly concerned about biodegradability. The term biodegradable is defined by international standards, as described above. Bioplastic films can be considered biodegradable yet leave residues of synthetic chemicals in the soil. This is not what we want on an organic farm!

Because all the bioplastic films contain a number of synthetic chemicals (in addition to plant-based materials), we wanted to know what happens to those chemicals after the visible breakdown of the mulch film. The TER indicated that these films have the potential to leave residues of synthetic chemicals in the soil. Plants have the ability to take up synthetic chemicals from the soil, and concentrate them in their tissues. For this reason, researchers have argued that more studies need to be done.

Cornucopia concurred, recommending that the petition to approve these materials be tabled until such research could be reviewed.

NOSB Vote

Biodegradable mulches were brought from petition to approval in an unprecedentedly fast seven months. This seemed unnecessarily rapid, particularly since this is an entirely new group of materials to be added to the National List.

Board member Zea Sonnebend stated upon reviewing a separate material, “When something is petitioned there’s usually at least a year in which you’re aware that the petition is in progress.” This gives the organic community a chance to do its own research and not exclusively depend on those with a commercial interest in a petition.

This longer time period allows public interest groups to read the scientific literature and evaluate the material with the interests of organic farmers and consumers in mind. In this case, a total of nine organizations either opposed bioplastic mulch or requested that the motion be tabled to allow time for further investigation. Groups expressing concerns, along with Cornucopia, included the Center for Food Safety, Beyond Pesticides, and Food and Water Watch.

Despite concerns raised by the public interest groups, the NOSB voted to allow biodegradable biobased mulch films as synthetic materials for use in organic crop production. The NOP advised that it would be easier to add bioplastic films to the National List if they were not called plastics. On the recommendation of the NOP, the NOSB’s wording of the proposal was modified to remove the term bioplastic, although these materials are indeed plastics. The trade group recognized the value of semantics—a “biodegradable biobased” film would be more acceptable to the organic stakeholders than a “bioplastic” film.

On the positive side, the definition of biobased was clarified, to include only “organic material in which carbon is derived from a renewable resource via biological processes. Biobased materials include all plant and animal mass derived from carbon dioxide recently fixed via photosynthesis.” This clarification eliminated the AACs (aliphatic-aromatic copolymers), which are made from petroleum.

Despite the potential advantages of bioplastic mulches, Cornucopia urges farmers to be cautious in using them. We don’t want to find out after the fact that organic produce contains residues of harmful synthetic chemicals.