Topic Paper: “Should We
Be Composting Plastic Coated Papers?”
By: Dan Matsch and Cyndra Dietz, Eco-Cycle Inc. (Boulder,
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 runoff.
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.
Most 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
Steve 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.”
John 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.
According 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 pieces.
Daniel 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