Study Finds Glitter Can Interfere With Aquatic Plant Photosynthesis

Not everything that sparkles is harmless. Glitter itself, for example, may be a surprisingly damaging environmental pollutant, according to a new study.

Although it is commonly linked with celebrations and light-hearted fun, glitter has a less appealing side. The study indicates that glitter particles can cut the amount of sunlight reaching water bodies, potentially limiting the capacity of certain aquatic plants to carry out photosynthesis.

Glitter as microplastic pollution

In effect, glitter is a microplastic disguised by its playful appearance, which can obscure its harmful role in plastic pollution. Attitudes have started to shift, however, as illustrated by the European Union's recent prohibition of microplastic glitter.

Like other microplastics, glitter generally does not break down easily, allowing it to remain and build up in the environment. It is also frequently too small for wastewater-treatment facilities to filter out, meaning it can enter waterways, where it may damage freshwater life or continue onwards to pollute the sea.

Researchers at the Federal University of São Carlos (UFSCar) in Brazil led the new study, which highlights a further concern.

Glitter flakes are plastic-usually Mylar, the researchers explain-but they commonly have a metallic coating as well, containing aluminium, bismuth, iron or titanium. According to the study, these metals may stop aquatic plants from receiving sufficient sunlight.

"These findings support the hypothesis we began with, which was that glitter interferes with photosynthesis, possibly owing to the reflection of light by the microplastic particles' metallic surface," says lead author Luana Lume Yoshida, a master's student at the Bioassay and Mathematical Modeling Laboratory (LBMM) in UFSCar's Department of Hydrobiology.

Glitter's effect on Egeria densa photosynthesis

The research examined large-flowered waterweed (Egeria densa), a macrophyte-an aquatic plant-that is native to Argentina, Brazil and Uruguay.

The researchers note that macrophytes of this kind fulfil numerous ecosystem roles, including supplying food, shelter, shade and oxygen to surrounding organisms.

They are also important for phytoremediation, in which plants are used to help remove toxins from polluted sites. Their ability to oxygenate water is likewise widely used in aquariums and artificial lakes.

Yoshida and her team placed 400 pieces of waterweed in flasks containing water collected from the Monjolinho reservoir on the UFSCar campus. They also used ordinary shop-bought glitter, whose particles had an average surface area of 0.14 square millimetres.

The team cultivated waterweed with 0.04 grams of glitter per litre of water, alongside waterweed grown without glitter as a control. Both sets were tested in light and in darkness.

The study found that photosynthesis rates were 1.54 times higher when glitter was absent. The researchers concluded that the minute glitter particles reduced light levels in the water. Plant respiration was also affected, although to a lesser extent.

Wider implications for aquatic ecosystems

Co-author Marcela Bianchessi da Cunha-Santino, one of LBMM's principal investigators, says that effects on a macrophyte such as this could extend much further through the ecosystem.

"In this experiment, we specifically observed the physical interference of glitter in a species of macrophyte, but there are better-known references in the scientific literature to water contamination and consumption of these particles by other aquatic organisms," she says.

"We put all the pieces of the puzzle together and were able to describe the functioning of the entire ecosystem, as well as pointing out what can happen throughout the food chain," da Cunha-Santino adds. "That's the key difference of an ecological approach."

Because relatively little research has examined the concentrations and characteristics of glitter dispersed through waterways, estimating the scale of the issue remains difficult. The concentrations used in this investigation were extrapolated from experiments involving different types of microplastic, so future field studies could provide more definitive figures.

Further research is plainly required to establish whether glitter blocks substantial amounts of light in natural aquatic ecosystems and how their inhabitants react. In the meantime, co-author Irineu Bianchini Jr., also a principal investigator at LBMM, argues that people should reconsider their use of glitter.

"For now it's important to warn society that changes in photosynthesis rates, however remote they may seem from our lives, are linked to other changes that affect us more directly, such as the decrease in primary production by food chains in aquatic environments," Bianchini Jr. says. "If there are more sustainable alternatives to glitter, why not switch to these right away?"

The study appeared in the New Zealand Journal of Botany.