How can we speed up plastic photodegradation?

Like human skin, plastics are susceptible to degradation due to ultraviolet (UV) light from the sun. Solar UV light that reaches our planet's surface has a wavelength between 280 and 400 nanometers, so it's not visible to the human eye, which sees light in wavelengths from roughly 390 to 750 nanometers.

Outdoors, UV light is present in amounts great enough to blitz polymer molecules. With enough exposure, UV light can cause a chemical reaction in the plastic, which results in scission, or severing, of those big polymer molecules.

Old-school plastics aren't particularly sensitive to sun exposure and as such, they could last for a very long time even in direct sunlight. However, with some clever molecular manipulation, or by integrating additives, engineers can make plastics that photodegrade much more quickly.

Certain chemical additives can make plastics more light-sensitive. Common additives (also called promoters, photosensitizers or accelerants) include ketone carbonyl, carbon monoxide carbonyl and different types of metal blends.

The carbonyls are types of organic compounds that are interlaced with plastic molecules. Other additives include metal salts, such as iron, cobalt, nickel which help to initiate a two-stage degradation process.

In the first stage, the additives absorb UV light and cause weak links in the polymers, so those big synthetic molecules get weaker and weaker. The second stage of the process happens as environmental factors like wind and waves bash and abuse the product, which leads to its eventual crumbling.

Blending plastic resins and additives takes trial and error, as engineers balance strength and non-toxicity, as well as degradation rates.

Photodegradable products react differently depending on many factors. The intensity of the UV radiation affects the rate of photodegradation. That means shade, cloud cover, and geographic location play a role in how much UV reaches that diaper your friend just flung out the car window.

The reality, though, is that most plastics won't see much time sunning on the beach. When a plastic product's use is complete, it usually winds up in a landfill or scattered in our environment. Only about 8 percent of plastics are recycled [source: EPA]. So when you consider that the United States alone creates more than 30 million tons of plastics each year, location matters, especially in terms of photodegradation.

In some cases, these light-sensitive plastics will break down in a landfill, but only if they receive a good dose of UV before they're plowed under. Other photodegradable plastics remain totally intact for untold years once they hit your local landfill. What's more, even those that totally disintegrate in the wild are often consumed by other organisms and as a result, can wiggle their way into our own food chain. No one can say for sure that the effects of plastics consumption are totally benign.

Currently, photodegradable kinds of plastics are really useful in situations involving littering -- intentional or otherwise. So for grocery sacks that blow into Grand Teton national park, at least there's hope that the sun will eventually take its toll.

In the end, this kind of degradable plastic is just one type of solution to a big problem: How do we humans deal with all of the plastic garbage we create? Right now, reusing and recycling are our best options, but in when plastics do go on jailbreaks and escape into the world, it's good to know that degradable plastics might not last as many generations as older types of polymer materials.

In 1960, plastics comprised only about 1 percent of solid waste in the United States. Now, that number is more like 12 percent. Most of these plastics go straight to the dump after we use them, a fact that highlights extreme wastefulness -- especially when you consider that plastics are easy for manufacturers to melt and reuse for new products.

Degradable plastics are a good tactic in our overall strategy for waste management. That's especially true for the roughly 4 billion plastic bags that become litter every year around the globe. But when it comes to long-term sustainability, we're better off recycling and reusing materials instead of constantly disposing of them.

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