Assessing the ecological consequences of biodegradable plastics: Acute, chronic and multigenerational impacts of poly-3-hydroxybutyrate microplastics on freshwater invertebrate Daphnia magna

Biodegradation is associated with the development of a biofilm on the surface of plastics, including P3HB microplastics.

“Biodegradation is associated with the development of a biofilm on the surface of the plastics [54], which applies also to P3HB MPs [45].”

• cites [54] Okeke, 2022, Ecotoxicological and health implications of microplastic-associated biofilms: a recent review and prospect for turning the hazards into benefits, Environ. Sci. Pollut. Res. Int. sourceNot checked — no full text of the source
• cites [45] Procházková, 2023, Effects of biodegradable P3HB on the specific growth rate, root length and chlorophyll content of duckweed, Lemna minor, Heliyon [Internet] sourceSupported

As the concentration of P3HB microplastics in suspension increased, the content of P3HB found in Daphnia magna increased.

“Furthermore, as the concentration of P3HB MPs in suspension increased, so did the content of P3HB found in D. magna [52].”

• cites [52] Procházková, 2024, Innovative approach for quantitative determination of ingested microplastics by Daphnia magna: use of differential scanning calorimetry and thermogravimetry, J. Therm. Anal. Calorim. sourceSupported

At a concentration of 25 mg/L, Daphnia magna ingested P3HB microplastics up to 10.3 wt% of MPs <63 μm and 6.3 wt% of MPs <125 μm.

“For example, at a concentration of 25 mg/L, D. magna ingested P3HB MPs up to 10.3 wt% of MPs <63 μm and 6.3 wt% of MPs <125 μm, respectively.”

• cites [52] Procházková, 2024, Innovative approach for quantitative determination of ingested microplastics by Daphnia magna: use of differential scanning calorimetry and thermogravimetry, J. Therm. Anal. Calorim. sourceSupported

Despite their biodegradability, microplastics from biodegradable polymers can persist for extended periods due to environmental factors such as temperature, humidity, pH, biologically active substances, and microorganisms.

“However, despite their biodegradability, these MPs can persist for extended periods due to the influence of various environmental factors (biotic and abiotic) environmental factors such as temperature, humidity, pH, biologically active substances, and the presence and activity of microorganisms [19,20].”

• cites [19] Agarwal, 2020, Biodegradable polymers: present opportunities and challenges in providing a microplastic‐free environment, Macromol. Chem. Phys. sourceSupported
• cites [20] Wei, 2021, Microplastics generated from a biodegradable plastic in freshwater and seawater, Water Res [Internet] sourceSupported

Daphnia magna is capable of non-selectively ingesting particles varying from <1 μm to approximately 70 μm in size.

“This filter-feeding species is capable to non-selectively ingest particles varying from <1 μm to approximately 70 μm in size [27,28].”

• cites [27] Schür, 2020, Microplastics but not natural particles induce multigenerational effects in Daphnia magna, Environ. Pollut. sourcePartly supported

  Section 4.3 (page unavailable) says D. magna readily ingests microplastics smaller than 90 μm and gives a filter-apparatus lower size limit of 200 nm, supporting the claimed size range. The paper does not establish that ingestion is non-selective; Section 4.4 (page unavailable) describes particle rejection behavior. (LLM, conf=0.82)

  Experimental — accuracy not yet measured
• cites [28] Frydkjær, 2017, Ingestion and egestion of microplastics by the cladoceran Daphnia magna: effects of regular and irregular shaped plastic and sorbed phenanthrene, Bull. Environ. Contam. Toxicol. sourceNot checked — no full text of the source

The ingestion of P3HB microplastics by Daphnia magna depends on both their size and concentration in the surrounding environment.

“As recently reported in our work [52], the ingestion of P3HB MPs depended on both their size and concentration in the surrounding environment.”

• cites [52] Procházková, 2024, Innovative approach for quantitative determination of ingested microplastics by Daphnia magna: use of differential scanning calorimetry and thermogravimetry, J. Therm. Anal. Calorim. sourceSupported

Biofilm formation on microplastics can modify their ingestion by organisms.

“Biofilm formation on MPs can modify their ingestion by organisms, for example, some MPs coated with biofilms can release into the water noxious signals, known as infochemicals, prompting nearby organisms to ingest them [55].”

• cites [55] Botterell, 2020, Bioavailability of microplastics to marine zooplankton: effect of shape and infochemicals, Environ Sci Technol [Internet] sourcePartly supported

  The Discussion (p. 8) says biofilms could give microplastics an infochemical signature that increases ingestion, and the Results (p. 6) report increased ingestion of microplastics infused with DMS. The paper did not test biofilm-coated microplastics releasing signals into water; it describes that pathway as a possibility and the signals as potentially attractive food cues, not noxious signals. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

In chronic and multigenerational experiments, increasing P3HB microplastic concentration corresponded with slower growth among mother D. magna.

“However, during chronic and multigenerational experiments, an increase in the concentration of P3HB microplastics corresponded with increased mortality, reduced reproductive activity, and slower growth among the mother organisms.”

For P3HB MPs <125 μm, a marginal stimulation of reproductive activity compared to the control group was initially observed up to a concentration of 25 mg/L.

“Notably, for the larger size fraction (MPs <125 μm), a marginal stimulation of reproductive activity, compared to the control group, was initially observed up to a concentration of 25 mg/L.”

For P3HB MPs <63 μm, a minor stimulation (3.3%) of reproductive activity was noted compared to the control group.

“In the subsequent experiment involving a lower concentration of P3HB MPs, a minor stimulation (3.3 %) of reproductive activity was noted for MPs <63 μm when compared to the control group.”

In the subsequent generations (F1-F3) of multigenerational experiments, a slight inhibition of reproductive activity was observed in all instances.

“However, in the subsequent generations (F1–F3), a slight inhibition of reproductive activity was observed in all instances (Fig. 2A).”

For P3HB MPs <63 μm, a slight delay in the average day of the first brood (up to 17.6%) was observed at all concentrations.

“Additionally, a slight delay in the average day of the first brood of juveniles (up to 17.6 % for MPs <63 μm, and 14.2 % for MPs <125 μm) was observed for both size fractions at all concentrations of P3HB MPs in suspension (Fig. 1B).”

For P3HB MPs <125 μm, mortality among mother organisms increased with concentration up to 46.7%.

“Moreover, an increase in the concentration of P3HB MPs in suspension led to elevated mortality rates among mother organisms for both size fractions (up to 43.3 % for MPs <63 μm, and 46.7 % for MPs <125 μm, Fig. 1C).”

At 100 mg/L P3HB MPs <125 μm, mortality among maternal D. magna was 46.7%.

“A substantial mortality rate among maternal organisms was recorded for both size fractions, specifically reaching 53.3 % for MPs <63 μm and 46.7 % for MPs <125 μm at a concentration of 100 mg/L (Fig. S1C).”

In multigenerational experiments, a delay in the first day of reproduction was observed in all cases.

“Furthermore, a delay in the first day of reproduction was observed in all cases (Fig. 2B) along with a slight increase in the mortality of mother organisms, consistent with the results of the chronic experiment (Fig. 2C).”

At 100 mg/L P3HB MPs <63 μm, mortality among maternal D. magna was 53.3%.

“A substantial mortality rate among maternal organisms was recorded for both size fractions, specifically reaching 53.3 % for MPs <63 μm and 46.7 % for MPs <125 μm at a concentration of 100 mg/L (Fig. S1C).”

For P3HB MPs <125 μm, a delay in the onset of the first brood was observed only at the highest concentration (100 mg/L).

“In addition, for MPs <63 μm, there was a delay in the onset of the first brood at high concentrations (50 and 100 mg/L), while for MPs <125 μm, this phenomenon was only observed at the highest concentration, i.e. 100 mg/L (Fig. S1B).”

For P3HB MPs <125 μm, a slight delay in the average day of the first brood (up to 14.2%) was observed at all concentrations.

“Additionally, a slight delay in the average day of the first brood of juveniles (up to 17.6 % for MPs <63 μm, and 14.2 % for MPs <125 μm) was observed for both size fractions at all concentrations of P3HB MPs in suspension (Fig. 1B).”

For P3HB MPs <125 μm, an inhibition of reproductive activity (12.2%) was monitored only at a concentration of 25 mg/L.

“Conversely, for MPs <125 μm, an inhibition of reproductive activity (12.2 %) was monitored only at a concentration of 25 mg/L of P3HB MPs in suspension (Fig. 1A).”

For P3HB MPs <63 μm, reproductive activity declined with increasing microplastic concentration, reaching 19.9% and 11.2% at concentrations 12.5 and 25 mg/L, respectively.

“However, the reproductive activity exhibited a decline with increasing microplastic concentration up to 19.9 %, and 11.2 % at concentrations 12.5 and 25 mg/L, respectively (Fig. 1A).”

In preliminary chronic experiments with higher concentrations (6.25, 12.5, 25, 50, and 100 mg/L) of both P3HB size fractions, reproductive activity of maternal D. magna diminished with increasing concentration.

“The preliminary experiments involving higher concentrations (6.25, 12.5, 25, 50, and 100 mg/L) of both size fractions of P3HB MPs in suspension revealed a diminishing reproductive activity of maternal organisms with increasing concentration (Fig. S1A).”

For P3HB MPs <63 μm, mortality among mother organisms increased with concentration up to 43.3%.

“Moreover, an increase in the concentration of P3HB MPs in suspension led to elevated mortality rates among mother organisms for both size fractions (up to 43.3 % for MPs <63 μm, and 46.7 % for MPs <125 μm, Fig. 1C).”

In chronic and multigenerational experiments, increasing P3HB microplastic concentration corresponded with increased mortality among mother D. magna.

“However, during chronic and multigenerational experiments, an increase in the concentration of P3HB microplastics corresponded with increased mortality, reduced reproductive activity, and slower growth among the mother organisms.”

In chronic and multigenerational experiments, increasing P3HB microplastic concentration corresponded with reduced reproductive activity among mother D. magna.

“However, during chronic and multigenerational experiments, an increase in the concentration of P3HB microplastics corresponded with increased mortality, reduced reproductive activity, and slower growth among the mother organisms.”

For P3HB MPs <63 μm, there was a delay in the onset of the first brood at high concentrations (50 and 100 mg/L).

“In addition, for MPs <63 μm, there was a delay in the onset of the first brood at high concentrations (50 and 100 mg/L), while for MPs <125 μm, this phenomenon was only observed at the highest concentration, i.e. 100 mg/L (Fig. S1B).”

For P3HB MPs <63 μm, a decline in the growth rate of mother organisms compared to the control was observed in the F2 and F3 generations (0.4% and 5.9%).

“For MPs <63 μm, a decline in the growth rate of the mother organisms compared to the control was observed in the F2 and F3 generations (0.4 % and 5.9 %).”

In the first generation (F0) of multigenerational experiments, a stimulation of reproductive activity was documented for both size fractions of P3HB (3.2% for MPs <63 μm, and 4.0% for MPs <125 μm).

“In the first generation (F0) of maternal organisms, a stimulation of reproductive activity was documented for both size fractions of P3HB (3.2 % for MPs <63 μm, and 4.0 % for MPs <125 μm).”

In the multigenerational experiment, growth of Daphnia magna decelerated in generations F1 to F3.

“In the multigenerational experiment, a slight inhibition of reproductive activity and a deceleration in the growth of organisms were observed in the subsequent generations F1 to F3.”

Smaller P3HB microplastics (<63 μm) elicited more pronounced effects on Daphnia magna than larger P3HB microplastics (<125 μm).

“The fact, that a more pronounced effect was observed with smaller particles (<63 μm) confirms our assumption that the impact of P3HB MPs on D. magna is particle size-dependent.”

• Also stated in: § Conclusion · hedged

  “Furthermore, smaller MPs appeared to elicit more pronounced effects.”

In chronic experiments, mortality of Daphnia magna increased with increasing concentration of both size fractions of P3HB microplastics in suspension.

“However, during chronic experiments, an increase in mortality alongside increasing concentration of both size fractions of P3HB in suspension was observed.”

• Also stated in: § Conclusion · plain

  “However, in chronic and multigenerational experiments, we observed an increase in mortality, a decrease in reproductive activity, and a slower growth rate of mother organisms, all of which were dependent on the concentration of P3HB MPs in suspension.”

P3HB microplastics did not induce acute effects on Daphnia magna, including no elevation in immobilization after 96 h in any tested scenario (suspension/leachate, juveniles/7-day-old organisms).

“Interestingly, the results of this study diverge from this pattern, as we did not observe an elevation in D. magna immobilization even after 96 h in any of the tested scenarios (suspension/leachate, juveniles/7-day-old organisms).”

• Also stated in: § Conclusion · boosted

  “This research has demonstrated that the presence of P3HB MPs did not induce acute effects on D. magna.”

In chronic experiments, reproductive activity of Daphnia magna was inhibited.

“Additionally, there was a progressive reduction in the growth of daphnia and an inhibition of their reproductive activity.”

• Also stated in: § Conclusion · plain

  “However, in chronic and multigenerational experiments, we observed an increase in mortality, a decrease in reproductive activity, and a slower growth rate of mother organisms, all of which were dependent on the concentration of P3HB MPs in suspension.”

In the multigenerational experiment, reproductive activity was slightly inhibited in generations F1 to F3.

“In the multigenerational experiment, a slight inhibition of reproductive activity and a deceleration in the growth of organisms were observed in the subsequent generations F1 to F3.”

In chronic experiments, growth of Daphnia magna was progressively reduced.

“Additionally, there was a progressive reduction in the growth of daphnia and an inhibition of their reproductive activity.”

• Also stated in: § Conclusion · plain

  “However, in chronic and multigenerational experiments, we observed an increase in mortality, a decrease in reproductive activity, and a slower growth rate of mother organisms, all of which were dependent on the concentration of P3HB MPs in suspension.”

Biodegradable polymers can naturally break down into small particles, generating a substantial quantity of microplastics.

“Comparable as conventional plastics, BDPs can also naturally break down into small particles, generating a substantial quantity of MPs [17,18].”

• cites [17] Fojt, 2020, A critical review of the overlooked challenge of determining micro-bioplastics in soil, Sci. Total Environ. sourceNot checked — no full text of the source
• cites [18] Sintim, 2019, Release of micro- and nanoparticles from biodegradable plastic during in situ composting, Sci. Total Environ. sourceNot checked — no full text of the source

The findings suggest that biodegradable microplastics may negatively affect freshwater ecosystems, given the important role of D. magna in the food chain.

“Given the important role of D. magna in the food chain, these findings suggest that biodegradable microplastics may indeed negatively affect freshwater ecosystems.”

• AssumptionRests on an assumption: The effects observed in laboratory experiments on D. magna can be extrapolated to natural freshwater ecosystems.

The adverse effects of P3HB microplastics on Daphnia magna in chronic and multigenerational experiments were dependent on the concentration of P3HB microplastics in suspension.

“However, in chronic and multigenerational experiments, we observed an increase in mortality, a decrease in reproductive activity, and a slower growth rate of mother organisms, all of which were dependent on the concentration of P3HB MPs in suspension.”

The impact of P3HB microplastics on Daphnia magna is particle size-dependent.

“The fact, that a more pronounced effect was observed with smaller particles (<63 μm) confirms our assumption that the impact of P3HB MPs on D. magna is particle size-dependent.”

Biofilm formation on the surface of P3HB microplastics facilitates their ingestion by Daphnia magna.

“The biofilm formation on the MPs surface also facilitates their ingestion.”

Mechanical blockage of the digestive tract due to accumulated P3HB microplastics probably led to increased mortality during chronic experiments.

“However, after a longer period (during chronic experiments), mechanical blockage of the digestive tract due to accumulated P3HB MPs probably led to increased mortality.”

The escalating mortality and growth inhibition of Daphnia magna with increasing P3HB microplastic concentration in suspension is probably related to a higher ingestion of P3HB microplastics from the suspension.

“Therefore, the escalating mortality and growth inhibition of D. magna with increasing P3HB MPs concentration in suspension (as depicted in Fig. 1C and D) is probably related to a higher ingestion of P3HB MPs from the suspension.”

Biodegradable microplastics can be comparable or even more hazardous to Daphnia magna than conventional microplastics.

“It is evident that biodegradable MPs can be comparable or even more hazardous to D. magna than conventional MPs, which requires careful consideration of their use and management to mitigate their potential environmental impacts.”