Biodegradation
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi.[a][2] It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradation occurs under a specific set of circumstances.
For the journal, see Biodegradation (journal).
The process of biodegradation is threefold: first an object undergoes biodeterioration, which is the mechanical weakening of its structure; then follows biofragmentation, which is the breakdown of materials by microorganisms; and finally assimilation, which is the incorporation of the old material into new cells.
In practice, almost all chemical compounds and materials are subject to biodegradation, the key element being time. Things like vegetables may degrade within days, while glass and some plastics take many millennia to decompose. A standard for biodegradability used by the European Union is that greater than 90% of the original material must be converted into CO2, water and minerals by biological processes within 6 months.
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Biodegradable technology[edit]
Biodegradable technology is established technology with some applications in product packaging, production, and medicine.[31] The chief barrier to widespread implementation is the trade-off between biodegradability and performance. For example, lactide-based plastics are inferior packaging properties in comparison to traditional materials.
Oxo-biodegradation is defined by CEN (the European Standards Organisation) as "degradation resulting from oxidative and cell-mediated phenomena, either simultaneously or successively." While sometimes described as "oxo-fragmentable," and "oxo-degradable" these terms describe only the first or oxidative phase and should not be used for material which degrades by the process of oxo-biodegradation defined by CEN: the correct description is "oxo-biodegradable." Oxo-biodegradable formulations accelerate the biodegradation process but it takes considerable skill and experience to balance the ingredients within the formulations so as to provide the product with a useful life for a set period, followed by degradation and biodegradation.[32]
Biodegradable technology is especially utilized by the bio-medical community. Biodegradable polymers are classified into three groups:
medical, ecological, and dual application, while in terms of origin they are divided into two groups: natural and synthetic.[18] The Clean Technology Group is exploiting the use of supercritical carbon dioxide, which under high pressure at room temperature is a solvent that can use biodegradable plastics to make polymer drug coatings. The polymer (meaning a material composed of molecules with repeating structural units that form a long chain) is used to encapsulate a drug prior to injection in the body and is based on lactic acid, a compound normally produced in the body, and is thus able to be excreted naturally. The coating is designed for controlled release over a period of time, reducing the number of injections required and maximizing the therapeutic benefit. Professor Steve Howdle states that biodegradable polymers are particularly attractive for use in drug delivery, as once introduced into the body they require no retrieval or further manipulation and are degraded into soluble, non-toxic by-products. Different polymers degrade at different rates within the body and therefore polymer selection can be tailored to achieve desired release rates.[33]
Other biomedical applications include the use of biodegradable, elastic shape-memory polymers. Biodegradable implant materials can now be used for minimally invasive surgical procedures through degradable thermoplastic polymers. These polymers are now able to change their shape with increase of temperature, causing shape memory capabilities as well as easily degradable sutures. As a result, implants can now fit through small incisions, doctors can easily perform complex deformations, and sutures and other material aides can naturally biodegrade after a completed surgery.[34]
Environmental and social effects[edit]
Plastic pollution from illegal dumping poses health risks to wildlife. Animals often mistake plastics for food, resulting in intestinal entanglement. Slow-degrading chemicals, like polychlorinated biphenyls (PCBs), nonylphenol (NP), and pesticides also found in plastics, can release into environments and subsequently also be ingested by wildlife.[46]
These chemicals also play a role in human health, as consumption of tainted food (in processes called biomagnification and bioaccumulation) has been linked to issues such as cancers,[47] neurological dysfunction,[48] and hormonal changes. A well-known example of biomagnification impacting health in recent times is the increased exposure to dangerously high levels of mercury in fish, which can affect sex hormones in humans.[49]
In efforts to remediate the damages done by slow-degrading plastics, detergents, metals, and other pollutants created by humans, economic costs have become a concern. Marine litter in particular is notably difficult to quantify and review.[50] Researchers at the World Trade Institute estimate that cleanup initiatives' cost (specifically in ocean ecosystems) has hit close to thirteen billion dollars a year.[51] The main concern stems from marine environments, with the biggest cleanup efforts centering around garbage patches in the ocean. In 2017, a garbage patch the size of Mexico was found in the Pacific Ocean. It is estimated to be upwards of a million square miles in size. While the patch contains more obvious examples of litter (plastic bottles, cans, and bags), tiny microplastics are nearly impossible to clean up.[52] National Geographic reports that even more non-biodegradable materials are finding their way into vulnerable environments - nearly thirty-eight million pieces a year.[53]
Materials that have not degraded can also serve as shelter for invasive species, such as tube worms and barnacles. When the ecosystem changes in response to the invasive species, resident species and the natural balance of resources, genetic diversity, and species richness is altered.[54] These factors may support local economies in way of hunting and aquaculture, which suffer in response to the change.[55] Similarly, coastal communities which rely heavily on ecotourism lose revenue thanks to a buildup of pollution, as their beaches or shores are no longer desirable to travelers. The World Trade Institute also notes that the communities who often feel most of the effects of poor biodegradation are poorer countries without the means to pay for their cleanup.[51] In a positive feedback loop effect, they in turn have trouble controlling their own pollution sources.[56]
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Etymology of "biodegradable"[edit]
The first known use of biodegradable in a biological context was in 1959 when it was employed to describe the breakdown of material into innocuous components by microorganisms.[57] Now biodegradable is commonly associated with environmentally friendly products that are part of the earth's innate cycles like the carbon cycle and capable of decomposing back into natural elements.
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