Biodegradable material vs non-degradable materials: s consumption of
compostable plastics less harmful than oil-derived plastics?
Walter Alain Martínez-Muñoz1, Jesús Guillermo
Jiménez-Cortés1, Cecilia Soldatini2,
Yuri V. Albores-Barajas3,4 & Alex
Córdoba-Aguilar1*
1 Departamento de Ecología Evolutiva, Instituto de
Ecología, Universidad Nacional Autónoma de México, 04510 Ciudad de
México, México.
2 Centro de Investigación Científica y de Educación
Superior de Ensenada - Unidad Académica La Paz, Calle Miraflores 334,
Bellavista 23050, La Paz, Baja California Sur, Mexico.
3 Secretaría de Ciencia Humanidades Tecnología e
Innovación. Av. Insurgentes Sur 1582, Col. Crédito Constructor. Alcaldía
Benito Juárez, C.P. 03240, Mexico City.
4 Departamento de Ciencias Marinas y Costeras,
Universidad Autónoma de Baja California Sur, 23080, La Paz, Baja
California Sur, Mexico.
*Corresponding author:
acordoba@iecologia.unam.mx,
Phone/FAX +52 555622-9003
Abstract
Given the harmful impact of plastics on organisms’ fitness, one question
arises: is compostable material (derived from non-oil sources) any
better? Here we assessed the fitness effects of consuming two
oil-derived plastics (polyethylene and polystyrene) and one compostable
product in insects, utilizing Tenebrio molitor beetles as the
study system. Animals were fed during the larval stage either of four
different treatments: a) polyethylene + apple/wheat; b) polystyrene +
apple/wheat; c) compostable product + apple/wheat; and d) apple/wheat
alone. Upon reaching the adult stage, insects were provided with wheat
and apple for 7 days, allowed to mate, and lay eggs. We recorded
developmental rate and mortality from larvae to pupa, weight and
fecundity, and survival probability from one stage to the next.
Mortality was higher when animals consumed any type of plastic. The
probability of survival was also affected, particularly in the pupal and
adult stages. Feeding with any type of plastic oil-derived or
compostable plastic led to a reduction in body size and reproductive
success (measured as surviving larvae). Notably, in some cases, the
group fed with compostable plastic was the most affected. Delays in
development at different stages could increase mortality, while the
decrease in egg production in females and the reduction in adult size
could imply carry-over effects on demography. Perhaps, the additional
materials in compostable products imply toxic effects like those caused
by plastics. Thus, the effects of compostable products are not any
better than those of plastics.
Key words: plastic, compostable material, fitness, insect,Tenebrio , life history, survival, weight, fecundity
Introduction
In a world full of threatening factors, plastics are part of the top
list of stressors (MacLeod, et al. 2021; Santos et al. 2021; Martinho et
al. 2022). Plastics are produced through the polymerization of monomers
derived from oil and gas. Two well-known examples are polyethylene (PE)
and polystyrene (PS) which are extensively used for plastic bags and
containers (such as Styrofoam®) respectively (Andrady & Neal, 2009).
Given the negative effects of these products, a proposed alternative is
the use of bioplastics such as compostable plastics (CP), which are
polymeric, non-oil derived materials from natural substances (Arikan &
Ozsoy, 2015; Atiwesh et al. 2021). Unlike plastics, CP production
presumably implies reduced greenhouse effects and energy-saving balance,
faster degradation (Atiwesh, et al. 2021).
Although there were doubts about the effects of plastic ingestion on
animal physiology, we now have a clearer understanding. Studies using
insects have shown negative effects at molecular levels, such as a high
production of reactive oxygen species, antioxidant enzymes, lipid
peroxidation indicators, and oxidative damage in Tenebrio molitor larvae fed with PE (Peng et al. 2023). Similarly, also in T.
molitor larvae, when PS was part of the diet, negative effects were
observed on the lipidome, with high levels of ceramides and cardiolipins
being produced, which are implicated in apoptosis and cellular stress
processes (Tsochatzis et al. 2022). At the DNA level, PS consumption
affected the expression of genes that encode heat shock and oxidative
stress proteins during development, specifically at the pupal formation
stage Chironomus riparius dipteran larvae (Carrasco-Navarro et
al. 2021). These negative effects also take place systemically. InC. riparius larvae, an increase in basal phenoloxidase activity
was found after PE ingestion (Silva et al. 2021). Also, Bombyx
mori larvae fed with PS, showed an increased expression of
antimicrobial peptide (AMP) genes, such as lysozymes and cecropins
(Muhammad et al. 2021).
While the environmental advantages of using non-petroleum-derived
plastics are known, there is still unconclusive evidence on their
effects on insects. For example, consumption of polybutylene adipate
terephthalate, a biodegradable and compostable copolymer, by T.
molitor larvae over 4 weeks did not affect survival, mass, or molting
rate (Kokalj et al. 2024). When black soldier fly was fed with the
biodegradable polyester polylactic acid (PLA), their larval development,
survival, as well as pupal development and rate, were not affected
(Heussler et al. 2024). Conversely, T. molitor larvae fed with
PBAT during the first and second generations, increased and decreased
their molting rate in the first and second generation respectively
(Kokalj et al. 2024). Finally, one other aspect that has lagged behind
is that of the effects of both non-biodegradable plastics and
bioplastics on insects when their ingestion is constant and long-term
(i.e., during all or almost all the larval phase until adulthood). These
elements are crucial since several future scenarios indicate that
plastic waste in the environment will be a constant for all organisms
across ecosystems.
Here we show the effects of ingesting plastic versus compostable
material on insect fitness (measured as development rate, mortality,
weight, hatching rate, fecundity, and survival probability among
different age stages) using the mealworm beetle Tenebrio molitor (Linnaeus, 1758) as our study subject. We chose this animal based on
previous research indicating that larvae can consume polymers for short
periods of time (Yang et al., 2015), and that microplastic, oil-derived
consumption impairs survival, growth, and development (Matyja et al.,
2020). The novelty of our work lies in its comparison of the fitness
effects of ingesting plastics vs CP, as well as in examining how fitness
surrogates covariate with each other. Our working hypothesis is that the
ingestion of biodegradable plastics will have little or no effect on the
variables analyzed, compared to PS or PE.