Fruit fly experiments shed new light on dangers of plastic ingestion
The evidence is starting to build around the ability of tiny fragments of plastic to make their way into all corners of the human body, with these particles recently discovered in living lungs and the bloodstream for the first time. What this means for our health is still a big unknown, but scientists have turned to trusty fruit flies as a model in search of answers to this question, tracking the particles through the intestinal tract to find they alter gene expression involved in stress response and oxidative damage.
Though research has started to paint a picture of what small plastic particles might mean for marine organisms, findings which include aneurysms in fish, impaired cognitive function in hermit crabs and swimming abnormalities in shrimp, our understanding of the human impacts is more limited.
Lab studies has shown they can alter the shape of lung cells and have toxic effects on human cells more broadly, but understanding how they behave inside the living body is another question entirely. To explore this, scientists at the Universitat Autònoma de Barcelona used one of the most well-understood of model organisms in the fruit fly Drosophila melanogaster, a long-favored tool for scientific research due to the large percentage of disease-sharing genes they share with humans.
The scientists say the fruit fly approach also overcomes some of the limitations in measuring plastic accumulation in human tissues. Working with polystyrene fragments of different sizes, the scientists used transmission electron microscopy to follow the path of the particles from their ingestion until they reached the haemolymph of fruit fly larvae, the equivalent to blood in humans.
This enabled them to produce a kind of "photographic report" revealing the behavior of the plastics as they interacted with microbiota and cells while moving through the intestinal tract. This revealed an ability to cross the intestinal barrier and enter the haemolymph. Though the scientists report no evidence of significant toxicity, the plastic particles did trigger broad molecular changes that altered the expression of genes involved in general stress response.
The particles also altered the gene expression associated with oxidative damage and damage to the DNA, along with genes relating to a response to physical damage of the intestinal barrier. The particles used in the study were 50, 200 and 500 nanometers in size, and interestingly, the scientists found that the smaller they were, the higher responses they induced.
"Our work adds information on what happens, in terms of effects, when the exposure is to nanoplastics, which, due to their small size, are of particular relevance to us, because of their greater capacity to break down biological barriers and produce toxicological effects that can affect the health of organisms, including humans," says Alba Hernández Bonilla, co-author of the study.
Studies continue to illuminate the wide variety of sources for human exposure to microplastics, with disposable coffee cups and plastic water bottles that shed huge amounts of particles into the liquids they contain among the key culprits. Meanwhile, scientists also consider airborne particles between 1 nanometer and 20 micrometers to be respirable, meaning that the particles at the center of this study may have a direct route into the body via inhalation.
"In addition to establishing a new methodological approach, our study confirms the great advantages of Drosophila melanogaster as a model to determine the potential harmful effects associated with the ingestion of these pollutants," explains Ricard Marcos, coordinator of the study.
The research was published in the journal Environmental Science: Nano.