The claim biodegradable is often associated with environmentally friendly products. What exactly does this mean? I would define it as being able to be broken down by natural processes, into more basic components. Products are usually broken down by bacteria, fungi or other simple organisms. By this definition, most chemicals are biodegradable; the only thing differing would be the amount of time it takes to break down. A piece of bread will break down rather quickly, whereas a piece of plastic will take decades and beyond.
Rate of breakdown may not be as important as what the product breaks down into. The ideal final products of any complex product of Carbon, Hydrogen, and Oxygen would be Carbon Dioxide(CO2) and Water (H2O). A majority of products are made mostly of these three elements. The previously mentioned piece of bread is made mostly of these, and after breaking down from complex sugars to simpler sugars, will eventually degrade to CO2 and H2O. This process would be accelerated if we ate the bread and our body would break it down and use it as energy, until only CO2 and H2O are left.
Biodegradation is the process by which organic substances are broken down by the enzymes produced by living organisms. The term is often used in relation to ecology, waste management and environmental remediation (bioremediation). Organic material can be degraded aerobically, with oxygen, or anaerobically, without oxygen. A term related to biodegradation is biomineralisation, in which organic matter is converted into minerals. Biosurfactant, an extracellular surfactant secreted by microorganism enhances the biodegradation process.
Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms. Some microorganisms have the astonishing, naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals. Major methodological breakthroughs in microbial biodegradation have enabled detailed genomic, metagenomic, proteomic, bioinformatic and other high-throughput analyses of environmentally relevant microorganisms providing unprecedented insights into key biodegradative pathways and the ability of microorganisms to adapt to changing environmental conditions.
In a perfect would all products would break down to CO2 and H2O. It gets more complicated with different chemicals. The banned pesticide DDT, is hazardous and toxic in its own right. It does biodegrade, rather slowly. The problem is that its breakdown products of DDD and DDE are even more toxic and dangerous than the original DDT.