Oysters are sensitive to fullerene nanoparticles.
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Ringwood, AH, N Levi-Polyachenko and DL Carroll. 2009. Fullerene exposures with oysters: embryonic, adult, and cellular responses. Environmental Science and Technology 43:7136–7141. |
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| South Carolina Oyster Restoration Enhancement. |
For the first time, research shows that nanoparticles called fullerenes are filtered out of water by oysters and taken up by their liver cells. The particles accumulated in special cell compartments and affected the cells' ability to regenerate and process nutrients. Adult oysters, embryos and liver cells that were exposed to moderate levels of the carbon-based nanoparticles were all sensitive to the fullerenes, possibly more than other aquatic animals tested to date.
Context
Nanotechnology deals with the developent and use of very small materials – called nanoparticles – that range in size from 1 to 100 nanometers. The field has been around for about half a century, but the development, production and use of these tiny particles have increased dramatically in the last two decades.
The engineered particles are made by combining atoms of different types of raw materials, such as carbon or metals. There many kinds of nanoparticles, and each has its own properties that dictate its use in products. Nanomaterials make products stronger, industrial processes more efficient and pharmaceuticals more effective. They are used as insulating materials and as stain-resistant coatings on fabrics, and are found in sports equipment, dental products, personal care products and electronics. It is estimated that up to 300 consumer products contain nanoparticles and many more applications are anticipated.
Nanoparticles can enter rivers, lakes and estuaries either from the facilities that produce them or after their use when they are disposed of into municipal or hospital wastewaters.
Fullerene C60 is a soccer ball-shaped nanoparticle. It measures one nanometer in diameter, contains sixty carbons, and is moderately stable; it has been used to deliver antibiotics to bacteria and anticancer agents to tumors. It is also common in optics and imaging products.
Its use in consumer products and biomedical applications has increased without an understanding of the kinds of effects it has on human health or the environment. It is known that nanoparticles like fullerene C60 do not dissolve well in water and often group together, forming aggregates up to 100 nanometers in diameter.
The American oyster – also known as the common or eastern oyster – is found in estuaries and in marine coastal areas in the Gulf of Mexico, along the eastern coast of the US and Canada, and in the Mediterranean Sea. They attach to rocks or other hard surfaces and feed on small particles, such as algae and bacteria. Oysters are important parts of the estuary and marine food chains because they filter particles out of the water.
Wild oysters have been fished for more than a century in North America but, in some areas, their populations have undergone recent severe declines due to overfishing, pollution, disease and loss of habitat. Globally, oyster fisheries have declined from more than 200,000 tons in the 1950s to about 105,000 tons in 2007. In contrast, global aquaculture production, mainly along eastern North America and parts of western North America, has quadrupled over the same time period to almost 100,000 tons a year. In the US, aquaculture production supplies about 30 percent of all American oysters.
Oysters are sensitive to pollutants and are used to understand the effects of human activities on estuarine organisms. In estuaries surrounded by heavy development, oysters may be consuming nanoparticles because the materials are similar in size to their normal diet. However, it is unclear whether nanoparticles enter cells or have any effect on the animals' health.
What did they do?
Researchers exposed adult oysters, their liver cells and 2-day-old embryos to different concentrations of fullerene C60 nanoparticles.
Adults were exposed for four days to either seawater alone or seawater containing four levels of fullerene C60 – 1, 10, 100 or 500 parts per billion. At the end of the exposures, the oysters were shucked and the liver (called the hepatopancreas) was dissected.
Liver cells collected from the adult oysters were analyzed for effects of the fullerene nanoparticles on lysosome health and function. Lysosomes are small organelles located inside of cells. They contain specialized proteins called enzymes that digest molecules and assist the cell with defense, development, repair and turnover. Lysosomes perform similar functions in oysters and many other animals, including humans.
In additional laboratory studies, oyster liver cells were grown in the presence of the fullerenes to understand whether the cells could take up the particles.
To check for developmental effects and survival, newly fertilized oyster embryos were also exposed for 48 hours to 1, 5, 10, 500 or 1,000 ppb fullerenes.
What did they find?
The results show for the first time that fullerenes do accumulate inside the cells of oysters. In addition, they affect the function of liver cells and the development of embryos of this invertebrate after very short exposures (hours to days).
At levels above 10 ppb, the fullerenes disrupted lysosome function inside the liver cells taken from the adult oysters. Severe effects were observed at 100 and 500 ppb. At these levels, lysosome function was decreased more than 40 percent – 2-3 times more than what was seen in unexposed adults. This large decrease in lysosome function has been associated in previous studies with reproductive failure in oysters.
Liver cells incubated with the fullerenes showed similar disruptions of lysosome activity. The fullerenes passed through the liver cell membranes after only four hours and collected in the lysosomes – but not in the nucleus. More severe effects on lysosome function were seen as doses of nanoparticles increased.
Oyster embryos were as sensitive to the nanoparticles as the adults. At 10 ppb fullerene concentrations and higher, fewer normal embryos were seen when compared to controls. Only 20 percent of the embryos developed normally at the highest levels of fullerene exposure.
This study used very short exposure times, and it is not known whether longer exposures to the nanoparticles would have increased the number of deformities in the offspring.
What does it mean?
Oysters are sensitive to fullerene nanoparticles and may be more affected by them than freshwater invertebrates or fish, according the results of the study. All oyster life stages tested – adults, cells and developing embryos – were impacted by exposure to the fullerenes.
The results also show that important cell processes are a major target of this type of nanoparticle. Disruption of lyosomes has been linked to several liver, cardiac and neurodegenerative diseases in people. For the oyster, exposure to the higher levels of fullerenes may cause long-term health problems and reduced survival and reproduction.
The research is important because few studies have been done on the effects of nanoparticles on marine or estuarine organisms like the oyster. The findings, though, are similar to prior oyster studies using another type of nanoparticle (quantum dots) and to studies with mussels, the authors note.
While environmental levels of fullerenes are not well known, this research shows that there is potential for these nanoparticles to affect the health of estuarine organisms. It is also important to consider that their uptake and effects occurred after only a very brief time - four hours to four days. According to the authors, the effects seen on the lysosomes at fullerene concentrations higher than 100 ppb are relevant and associated with reproductive failure in the mollusks.
In the wild, oysters living in estuaries surrounded by developments and high populations could be continuously exposed to these types of nanoparticles. The oysters may accumulate nanoparticles in their bodies and cells since they filter and remove similar sized particles from the water. According to the authors, “these studies indicate that significant inputs to estuarine environments should be carefully evaluated to avoid significant sublethal impacts on oysters and other biota.”
ResourcesCrassostrea virginica (Eastern oyster). Cultured Aquatic Species Information Programme. Food and Agriculture Organization of the United Nations. Eastern oyster. Bay Field Guide. Chesapeake Bay Program. Nanotech FAQs. National Nanotechnology Initiative. Nanotechnology White Paper (PDF). 2007. US Environmental Protection Agency. EPA 100/B-07/001, February. |
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