Aerospace and medical device breakthroughs are sharply increasing demand for special materials called carbon nanofibers, but these emerging compounds could add to a long list of pollutants that inadvertently poison animals — particularly Amazonian turtles.
When these substances find their way into a turtle's system, they appear to cause defects that can lead to lasting outcomes, including brain damage. A study published March 17 in Science of the Total Environment investigated these dangers by exposing one such reptile, Podocnemis expansa, to the novel and renowned carbon nanofibers, or CNFs.
Exposed turtles exhibited increased blood-cell abnormalities, fragmented sections of those cells' DNA, general damage to the cells and neurological implications.
"The results in the present study have confirmed the hypothesis that the prolonged exposure of P. expansa juveniles to CNFs — at environmentally relevant concentrations — induces predictive mutagenic, genotoxic, cytotoxic and neurotoxic effects," said Guilherme Malafaia, an author of the study and a postdoctoral researcher at Goiano Federal Institute and the Federal University of Goiás, in Brazil.
All of these issues threaten serious long-term effects. For instance, one cytotoxic consequence of exposure is more blood cells taking part in apoptosis, or "cell suicide," potentially lowering overall blood-cell count.
Among the hottest topics in technology, carbon nanofibers are microscopic in size yet incredibly strong and stable, with excellent mechanical properties. With that unique duality, they're ideal materials to use when engineering complex electronic devices and batteries. Carbon nanotubes are even considered as vessels for drug delivery.
However, despite the growing prevalence of carbon nanofibers, Malafaia noted that the risks they pose to animals are still virtually unknown. That's a problem because — like other pollutants, such as mercury and oil from industrial waste — these materials could be disposed of in the environment and eventually reach ecosystems.
"The first step in proposing pollution mitigation or remediation measures is undoubtedly to identify the impacts of pollutants on organisms," Malafaia told The Academic Times. "The lack of knowledge about the negative effects of pollutants discourages any motivating action."
He urged policymakers and scientists to remedy this gap in the literature — the former by creating stricter laws on the disposal of materials containing carbon nanofibers, and the latter by conducting further studies.
To assess the potential impact of these fibers, Malafaia's team conducted many toxicological screenings on the Amazonian turtles exposed to the fibers in small amounts over the course of several months.
These mostly solitary turtles, also called Arrau turtles, tend to swim along river currents and can weigh more than 100 pounds. Found mainly around South America, they are listed by the International Union for Conservation of Nature as conservation-dependent, or in need of conservation to protect from extinction.
The team's findings are also important because reptiles such as the research subjects are "little studied in the ecotoxicological area," Malafaia noted.
"Much research focuses on studying the effects of pollutants on macroinvertebrates, algae and fish," he said. "Assessing the impacts of emerging pollutants on a poorly studied group of animals is of great relevance."
Although the exact degree of effect is still unaccounted for, Malafaia observed that when the turtles were exposed to carbon nanofibers, the materials accumulated in the liver and the brain.
Once in these organs, the fibers appeared to heighten the activity of the enzyme acetylcholinesterase.
"It is an enzyme that catalyzes the breakdown of acetylcholine and of some other choline esters that function as neurotransmitters," Malafaia explained. "The consequences of this increase include different changes in the animals' nervous system."
That is a novel finding, according to the researcher, because many previous studies reported the inhibitory effect of pollutants on this enzyme. For carbon nanofibers, the new study found the opposite.
The discovered toxicological consequences in these animals point to possible future neurological and physiological defects. The nanofibers also prompted oxidative stress in the turtles. In humans, this condition leads to symptoms such as neurodegenerative diseases, high blood pressure and even cancer.
"In the brain and liver of animals, we observed that CNFs were able to cause changes in oxidation-reduction systems — indicative of oxidative stress," Malafaia explained.
Oxidative stress is caused by a redox imbalance, which occurs when a bodily mechanism that is supposed to neutralize substances that are harmful to cells can't keep up with production of these substances, such as reactive oxygen or nitrogen species, also called free radicals.
"Excess free radicals can damage cellular structures, including DNA and membranes," Malafaia said. "And if production exceeds the body's ability to control them, oxidative stress will result."
Malafaia emphasized that this study should serve as a warning for the ecotoxicological risks related to carbon nanofibers. But he added that it is important that the findings be built upon, specifically regarding which factors may mitigate or enhance the effects of carbon nanofiber poisoning in these turtles.
For example, scientists could assess whether the effects of exposure are reversible, whether the consequences of these pollutants remain after the exposure period ends, and whether sex or age have anything to do with susceptibility.
"By demonstrating that CNFs, even in small concentrations, affect the biology of Amazonian turtles, we expect society in general to become aware of the importance of not discarding materials in the natural environment," Malafaia said.
The paper, "Multiple toxicity endpoints induced by carbon nanofibers in Amazon turtle juveniles: Outspreading warns about toxicological risks to reptiles," published March 17 in Science of the Total Environment, was authored by Abraão Tiago Batista Guimarães and Guilherme Malafaia, Goiano Federal Institute and Federal University of Goiás.