Marine animals eat microplastic particles and excrete them in their feces, endangering the marine environment.
A new study by Tel Aviv University has revealed alarming findings regarding the spread of microplastic particles in the marine food web. Following numerous studies on the dangers of marine animals ingesting non-biodegradable microplastic particles, the researchers sought to examine what happens to microplastic particles after they pass through the digestive tracts of marine animals. The findings indicate that the particles are excreted in the feces of marine animals, so that the marine environment may recognize them as organic matter that can be eaten. According to them, another danger floating on the surface of the water is the accumulation of feces and plastic particles, which can cause an increase in the amounts of carbon and nitrogen at the bottom and lead to algal blooms, which also have a critical impact on the balance of the marine food web.
Feces and microplastics: the new danger to life underwater
The research was conducted by doctoral student Eden Harel. from the School of Zoology in the George S. Wise Faculty of Life Sciences, Prof. Noa Shenkar from the School of Zoology and the Steinhardt Museum of Nature, and Prof. Ines Zucker from the School of Mechanical Engineering At the Ivy Walder Fleischmann Faculty of Engineering, And from the Porter School of Environmental StudiesThe article was published in the journal Chemosphere.
Prof. Shenkar explains: "About a decade ago, when awareness of the plastic problem in the marine environment began to rise, many researchers were concerned with detecting microplastic particles and asking where they end up and what is the scope of the problem? Recently, the research focus has shifted to the issue of the effects of microplastics and the damage they cause. However, a significant portion of the experiments in this field are performed with purchased, clean plastic, while in the sea, plastic particles are exposed to many and varied effects and pollutants. We sought to examine whether and in what way plastic changes after passing through the digestive system of a marine animal, and how the process affects the presence of plastic and its availability to other animals."
The researchers built an experimental setup in the laboratory that simulates seawater and contains ciliates, marine animals that feed by efficiently and indiscriminately filtering tiny particles in the water. They exposed the ciliates to two types of plastic particles: a widely used conventional plastic called polystyrene (PS), and a type of plastic called polylactic acid (PLA), which is marketed as a biodegradable and environmentally friendly bioplastic. They then examined the effect of the ciliates' filtering process on the concentration and distribution of plastic particles in the water at four time points: at the moment of exposure; two hours later – after the ciliates had finished filtering the entire volume of water available to them in the system and had effectively 'swallowed' all the microplastic particles; 24 hours later; and 48 hours later – after the digestion process was complete and feces were excreted into the water.
The findings revealed that approximately 90% of the regular plastic particles were removed from the water after two hours of filtration, but after 48 hours, after passing through the fish's digestive system, all of the particles returned to the water. In contrast, the concentration of bioplastic particles in the water decreased significantly and was maintained for 48 hours, but it is likely that some of the relatively large bioplastic particles disintegrated during digestion and returned to the water as smaller particles.
"The many changes that plastic particles undergo when they are in the environment, from aging processes to the process we investigated in this article, mean that plastic particles actually serve as spreaders of pollutants and diseases in the food web."
In the second phase, the researchers examined what happened to those particles that were filtered, digested, and excreted back into the water column. To do this, they isolated microplastic particles from the fish's feces and examined them using Raman spectroscopy: an advanced instrument that identifies the chemical composition of the material being tested based on the scattering of a laser beam reflected from it.
"We found that the sensitive device does not notice that it is plastic at all, and identifies the particle as another organic material," explains Eden Harel. "It turned out that the microplastic particles are excreted from the digestive system of the eel when they are coated with a shell of feces, and it can be assumed that the marine environment also recognizes those particles as organic material. Since many marine animals feed on feces, they may well recognize the plastic that has changed its properties as food. In this way, they too are exposed to microplastics, and pass it on through the marine food web."
Prof. Zucker adds: "The fecal envelope may serve as a substrate for bacterial colonization and also increase the adhesion and accumulation of pollutants such as heavy metals and residual organic substances (such as antibiotics) on the surface of the particles. This phenomenon does not spare plastic marketed as 'biodegradable': as long as conditions are not given that allow for its complete decomposition, it will be found as a particulate contaminant that changes its appearance as it passes through the digestive system. The many changes that plastic particles undergo when they are in the environment, from aging processes to the process we investigated in this article, mean that plastic particles actually serve as spreaders of pollutants and diseases in the food web."
Eden Harel, a specimen at sea (Photo: Eden Harel)
Sinks quickly and depletes nutrients
In the third phase of the study, the researchers focused on the opposite effect: whether and how microplastic particles affect feces – an organic material that is of great importance in marine ecology. "We found that plastic changes important physical properties of feces. Normal feces sinks in the water column at a very slow rate and along the way serves as food for many animals. Feces containing microplastic particles, on the other hand, sink quickly to the bottom. This removes an important nutrient from the water column, while an accumulation of feces and plastic particles is created on the bottom. This accumulation can cause an increase in the amounts of carbon and nitrogen in the bottom and lead to algae blooms – another critical effect of microplastics on the balance of the marine food web," says Eden Harel.
The researchers conclude: "In this study, we revealed significant aspects of the influence of filter-feeding animals on the characteristics of microplastic particles in their environment, and in the marine food web in general. The most worrying conclusion is that the microplastic problem is much more complicated than we initially thought. The damage caused by plastic to the marine environment has many aspects that we did not imagine, its complexities are only increasing, and sometimes both we and the environment are unable to recognize that it is plastic. As time goes by, plastic is harming more and more marine ecosystems, and it is our duty to develop new technologies that will minimize this dangerous phenomenon."
More of the topic in Hayadan:
