Topic Paper: “Should We
Be Composting Plastic Coated Papers?”
By: Dan Matsch and Cyndra
Dietz, Eco-Cycle Inc. (Boulder, CO.)
Eco-Cycle staff has raised concerns about the environmental impact of
plastic remnants in compost that could result from the incorporation of
plastic-coated paper products (such as cups, plates, milk cartons) into compost
systems. Since disposable products like these are increasingly coated
with plastic (usually LDPE or HDPE), (which is not known to biodegrade) instead
of wax (which does biodegrade), their inclusion in compost program feedstock
could result in the accumulation of small and sometimes microscopic plastic
remnants in the soil. This could be particularly problematic after the repeated
application of finished compost. Considering the known persistence of plastics
in the environment, and the documented mortality rate of a variety of species
(due to ingestion and/or entanglement) in terrestrial, marine and freshwater
ecosystems, we wanted to know how plastic remnants would affect the smaller
organisms that are essential to soil health. We also wanted to know how it
would affect adjacent aquatic ecosystems that would receive plastic from soil
We contacted a variety of experts around the US to help
us better understand the physical and biological impacts of plastic remnants in
compost when applied to the soil.
papers used for foodservice items are coated with a non-biodegradable polymer
in order to improve moisture or grease resistance. Most of these are HDPE and
LDPE coated. According to Steve Mojo of the Degradable Products
Institute, these polymers inhibit the microbes’ ability to break down
material and retard the breakdown of the paper itself.
Mojo also concludes that these plastic coatings remain in the compost and will
not degrade for long periods of time. On a similar note, William Brinton, Ph.
D., of Wood End Laboratory, noted that in his research the HD and LD
polyethylenes will only break down into smaller pieces and not biodegrade.
Research by Natasha Page at the University of Alberta has shown similar results
and has demonstrated erosion-movement of plastic fines into surface waters,
where they may wreak havoc on aquatic life.
The authors of the study “Decomposition of coated papers from a
quick-service restaurant” (Tappi
Journal, Vol. 78, No. 5, by Ian N. Davie, Julien P. Winter, and R.
Paul Varoney), found that, “Polyethylene films do not biodegrade under
normal outdoor conditions.” They studied “the biodegradation rate
of waxed paper, polyethylene-coated paper, and uncoated paper and evaluated
under composting conditions and in soil at room temperature.” They
found that “Petroleum wax degrades readily and serves as a
metabolic energy source.” During the study “analysis for residual
polyethylene in the polyethylene-coated paper soil degradation samples
indicated no degradation of the polyethylene.” The authors also noted
that “ the residual plastic film appears to be too thin and fragile to be
conventionally screened from the finished compost.”
Springman, of Ramsey County (MN) Environmental Health, points out that
depending on how much plastic is in the finished product and how many times it
is applied over many years, enough of the plastics present could build up to
cause drainage and other physical characteristics of the soil to change.
to Steve Mojo, plastic fragments will migrate with water runoff or can be blown
with the wind. Jim McNelly, of Renewable Carbon Management LLC, has done
composting research that found “pond scum” of micro LDPE
Dindal, Ph. D., Professor Emeritus of Soil Ecology, the State University of New
York (SUNY) College of Environmental Science and Forestry, has done specific
research on plastics incorporated into soil and compost.
Dr. Dindal did two studies in 1983 and 1990. Rigid
polyethylene and polystyrene solids were ground up to sand size. These were
mixed separately with soil and cow manure to the following percentages of
plastic by volume: 5%, 30%, 60%, and 90%. Earthworms were added to some of the
samples. Normal populations of native soil microbes and other soil
invertebrates were present in the soil and manure prior to testing.
the percentage levels for plastic, microbial respiration was reduced during the
study, which indicates a marked decrease in microbial population levels.
This may be due to the decrease in soil moisture. When earthworms were added, the worms ingested the polyethylene
particles, many of which then penetrated their gut tissue causing death. The
earthworms did not ingest the polystyrene, they fed around it.
from this study (as stated by Dr. Dan Dindal, 2/05):
1. There is no evidence that microbes are
able to decompose polyethylene or polystyrene.
- Our two studies show that particulate HDPE and PS
cause detrimental effects on soil microbes and soil invertebrates. These
soil creatures are responsible for composting and soil organic matter
formation and incorporation.
- Earthworm populations were depressed or killed in
all PE concentrations.
- Soil moisture content is negatively correlated to
the concentration of plastics in soil creating a potential
stress effect on the soil biota, which could lead to a decrease in
- Plastic build-up via repeated applications is a
serious possibility that can lead to the marginalization of soil
structural characteristics and fertility as we know it. Once the
recalcitrant plastic polymers are distributed in soils, we may never be
able to reverse the condition affecting the value of farm land.
Additional Studies using fragment and thin sheet
polyethylene instead of granulated would be of interest.
Additional opinions: The
following offered their professional opinions. However, these experts stressed
that they have not done specific research on this subject. Dr. Dindal’s
work is the only actual research that we found.
Mike Weintraub, Ph. D., a microbial biologist and
research assistant at the University of Colorado-Boulder, thought that there is
a potential for plants to absorb hydrocarbons that have leached from plastics
present in compost.
Jeanette Norton, Ph. D., an associate professor of
soil microbiology at Utah State University, pointed out that
risks for soil toxicity include plasticizers and pigments that are present in
plastics and that could migrate into soils.
Patrick Bohlen, Ph. D., Director of Research at MacArthur
Agro-Ecology Research Center, Florida, noted that earthworms are highly
susceptible to toxins in the soil and are used as indicator species. They would
be affected by any compounds leaching from plastics. He also mentioned concern
about the build-up of plastics in the soil over time from repeated applications