Floral foam study – understanding the science

Microplastics researcher Dr Charlene Trestrail responds to a statement by floral foam manufacturer Smithers Oasis.

A small aquatic animal 'Daphnia magna' with a gastrointestinal tract full of floral foam particles. Image: Dr Charlene Trestrail.

In November 2019, a research paper entitled “Foaming at the mouth: Ingestion of floral foam microplastics by aquatic animals”, was published by a leading international academic journal Science of the Total Environment.

This study, undertaken by scientists from RMIT University in Australia, showed that floral foam can harm the health of aquatic animals.

The results prompted foam manufacturers Smithers Oasis to issue a press release on the 19th December 2019, with a detailed response to the study’s findings and its methodology.

As a supporter of independent, peer-reviewed science, the Sustainable Floristry Network wanted to offer the study’s scientists an opportunity to respond to each of the three criticisms detailed in the press release.

In the following text, Dr Charlene Trestrail, lead researcher on the 2019 floral foam study, and now Research Associate, Climate Change Cluster, Faculty of Science, University of Technology Sydney, provides a response to this press release.


Issue #1 raised by Smithers Oasis in press release

First, the publication does not reflect real-world conditions. The test subjects were harvested, transferred to a laboratory environment, and literally “starved” by the researchers before being fed a diet of only crushed floral foam in water filtered to prevent naturally occurring algae and bacteria from influencing results. It is hardly surprising that the test subjects ingested the foam in these conditions. As the authors conceded, “the ingestion of these microplastics was likely driven by the physical presence of the microplastics” in the absence of anything else.

Dr Trestrail’s response:

1) The study presented seven species of aquatic animals with microplastics generated from floral foam. All seven species chose to eat the microplastics.

2) To put these results into context, it is important to understand that even small aquatic animals, like the species used in our study, are selective about what they eat.

  • Because animals are selective feeders, it means they do not eat inorganic particles just because they are hungry. An example of this is that pet fish do not eat the sand in the bottom of their fish tank when they are hungry.
  • Animals decide whether to eat a particle based on that particle’s physical characteristics, such as its size and shape. Some animals also consider the chemical characteristics of a particle, such as the surface charge and how it ‘smells’ (chemoreception) to the animal (Kamio and Derby, 2017; Rosa et al., 2013; Taghon, 1982). After assessing the physical and/or chemical characteristics of a particle, the animal will decide whether to ingest or reject the particle.
  • In our study, animals chose to eat the floral foam microplastics. We concluded that this was because physical characteristics, rather than chemical characteristics, signalled to the animals that the foam microplastics were food particles. We made this conclusion based on our observation that animals ingested both regular floral foam and biofoam, which we expect to differ in chemical composition. Specifically, we say in the article:

“Since we saw no difference in ingestion between regular foam microplastics and biofoam microplastics, we conclude that the ingestion of these microplastics was likely driven by the physical presence of the microplastics.”

3) As stated in the research article, we did not simultaneously offer animals foam microplastics and food (like algae or bacteria) because this could have increased the likelihood of animals choosing to eat the foam microplastics.

  • Algae and bacteria attach to the surface of microplastics, and this can increase the likelihood of animals choosing to eat microplastics (Vroom et al., 2017).

Therefore, offering animals food particles and microplastics simultaneously could have biased the results by making it more likely that animals would have chosen to eat the microplastics.

By choosing not to offer animals food along with the microplastics, we avoided the risk of biasing the results towards ingestion.

Issue #2 raised by Smithers Oasis in press release

Second, “No mortality was observed during the experiment,” and the small group of biomarkers for which the authors collected data showed only effects without statistical significance, if at all. The authors were left expressing uncertainty about certain data they reported due to the conceded presence of “confounding factors,” and speculating about how changing the test parameters, such as “modifying exposure time or selecting a different age class” of test subjects “could have yielded statistically significant results.”

Dr Trestrail’s response:

1) We found that eating floral foam microplastics did not kill the aquatic animals we tested. However, just because an animal is alive, does not mean it has optimal health or that the microplastics in its gut have had no effect.

  • Many studies found that eating microplastics often does not kill an animal (Galloway et al., 2017).
  • Even though an animal is alive, microplastics in the gut can slow the animal’s growth rate and reduce the number of offspring it produces (some of the many studies reported such results are Leung and Chan, 2018; Sussarellu et al., 2016; Ziajahromi et al., 2018). Additionally, it has been widely reported that ingested microplastics affect animals at the cellular level (Prokić et al., 2019).
  • This means that measuring death alone does not accurately reflect the effects of microplastics on animals.

2) It is common to test the effects of pollutants using ‘biomarkers’. These are measurements of enzymes or molecules inside a cell that gives us information about the health status of an animal after the animal encounters pollution (Walker, 1995).

  • We measured four biomarkers of cellular stress, which are used regularly in microplastics research (Prokić et al., 2019).
  • We saw changes in the concentration of some of the biomarkers we measured, but these changes were statistically insignificant. However, taken together, the biomarker results show an interesting trend that suggests eating floral foam microplastics caused animals to experience cellular stress. In the article, we discuss the limitations of our data and suggest ideas for improvement for future studies.

3) Biomarker responses to pollution can be influenced by characteristics of the individual animal. For example, biomarker responses can differ between young and old animals, or between different seasons (Leiniö and Lehtonen, 2005; Viarengo et al., 1991).

  • This means that although some of our biomarker responses were statistically insignificant, these responses might all be significant in, for example, younger animals than the ones we tested.
  • Further studies need to be conducted to determine whether floral foam microplastics affect animals differently depending on age or season.

Issue #3 raised by Smithers Oasis in press release

Third, the publication appears to have been prompted by what the authors describe as a “viral social media trend” involving “videos of people using their fingers to crush blocks of floral foam” that purportedly “generates innumerable microplastics.” The authors provided no data or analysis about the scope of their conjecture regarding “threats” to the biological subjects of their laboratory experiments instead apparently secure in leaving such subjects to the realm of the imagination.

Dr Trestrail’s response:

1) As stated in the research article, this study was conducted because no other studies have explored the effects of phenol-formaldehyde microplastics on animals.

  • Eating microplastics can affect animals differently depending on the type of plastic in the microplastic particle (Lei et al., 2018).
  • When we conducted our research, no studies had looked at the environmental effects of phenol-formaldehyde microplastics (de Sá et al., 2018). To address this knowledge gap, we conducted our study on phenol-formaldehyde microplastics.
  • We used floral foam as the source of phenol-formaldehyde microplastics in our study because is an accessible source of phenol-formaldehyde plastic that readily crumbles into microplastics. In particular, we used Oasis products because this company manufactured ‘biofoam’; this gave us the opportunity to compare how regular foam and biofoam affected animals.
  • The fact that floral foam is also used in a social media trend emphasised the need to understand the effects of phenol formaldehyde microplastics in the environment. This social dimension does not detract from the scientific value of our study.

2) The quality of our study was evaluated by several anonymous peer-reviewers and a journal editor before it was accepted for publication.

3) Our study concluded that floral foam microplastics can pose a threat to aquatic animals. We made this conclusion based on the results of our study, that:

  • floral foam microplastics leached chemicals into the surrounding water, and these chemicals were more harmful to aquatic animals than chemicals that leached from other plastic products (Lithner et al., 2012, 2009).
  • the biomarker trends we observed in our study suggest that eating floral foam microplastics caused cellular stress to animals.
  • animals chose to eat floral foam microplastics, and therefore this type of microplastic could cause the same effects that other types of microplastics cause (i.e. reduced growth and reproduction).
  • Our conclusions are supported by the recent research of Klun et al (2022), who – like us – determined that phenol-formaldehyde microplastics are eaten by the aquatic crustacean, Daphnia, and leach toxic chemicals into the surrounding water. Additionally, Klun et al found that the chemicals that leach out of phenol-formaldehyde microplastics are toxic to aquatic plants.


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