The abstract for the study says that "most life-cycle studies have found that a reduction of greenhouse gas emissions can be achievable by replacing petroleum-based plastics with bioplastics made from renewable feedstock, but these analyses have failed to count the carbon emissions that occur as farmers worldwide convert forest and grassland to new cropland to replace the corn diverted to bioplastics. By excluding emissions from land use change, most previous accountings were one-sided because they counted the carbon benefits of using land for bioplastics but not the carbon costs, the carbon storage, and sequestration sacrificed by diverting land from its existing uses."

Obviously corn is not the only crop to be converted into bioplastics. There is also sugar cane, switch grass and other biomass, some produced as the result of processing these food crops into their final product, as is the case with sugar cane and sugar beets, rather than turning the actual food into plastic. The authors of the paper point this out.

"Accounting for the land use change, emissions can limit the attractiveness of bioplastics for the displacement of petroleum-based plastics, at least from an environmental point of view. The use of agricultural by-products as a bioplastic feedstock is a valid solution to the problem. Alternatively, recycling of bioplastic waste could contribute to reducing the land use change emissions. From this point of view, it is clear that the incineration or land-filling of the bioplastic products is not a valid alternative for a real solution of the problem."

The CO₂ coming from crop harvesting and processing is not captured and sequestered, but is released into the atmosphere. Is that counted in the footprint of making bioplastics?

Water usage to grow the crops in sufficient quantity to result in enough biomass to produce tons of plastics needed for the production of single-use items such as water bottles, deli containers and other food containers, is a huge issue. This comes at a time when there are rising concerns about the global availability of potable water.

Land use encompasses thousands of acres of land on which crops are grown; the fossil fuels used to spray the crops with pesticides (not to mention the use of pesticides themselves); and the harvesting of crops. The energy it takes to process the crops into the bioplastic also must be considered.

Another paper published in 2009 by Brian Momani at Worcester Polytechnic Institute, "Assessment of the Impacts of Bioplastics: Energy Usage, Fossil Fuel Usage, Pollution, Health Effects, Effects on the Food Supply, and Economic Effects Compared to Petroleum Based Plastics," noted that the mainstream news media "generally paint an over-optimistic picture of the use of biomaterials in plastics. Bioplastics have many advantages over petro-plastics but they have yet to live up to the hype. When all factors are taken into account, replacing a significant portion of plastics with bioplastics is not a viable option at this time."

Momani points out the attractive attributes of bioplastics, which do not use petroleum or natural gas feedstocks, meaning that ultimately they emit less carbon dioxide over their life cycle. "Bioplastics consume less energy to produce than petroleum-based plastics and have fewer health concerns associated with them. Also, bioplastics are generally compostable."

That last statement is proving less true, as more experiments with composting are conducted showing that compostability is dependent upon high heat, microbes and the overall environment and that many bioplastics won't compost or even degrade in a reasonable amount of time.

The "serious shortfalls" of bioplastics, Momani writes, is that "bioplastics production is often more energy-intensive than petro-plastic production due in large part for the need for agricultural inputs in addition to the actual plastic processing."

Another shortfall of bioplastics is that they are more expensive than petroleum-based plastics. Numerous studies over the past decade have shown that consumers are resistant to paying a lot more for "green" products—they will pay a bit more, but not enough to make bioplastics profitable. That could be because of the "immaturity" of the market, said Momani.

A more likely scenario from the way I see it, is that bioplastics cannot be made in quantities that make production cost-effective; if they could be, demand would follow. Bioplastics is a niche market—it always has been and always will be—because bioplastics don't offer what plastics were developed for: Strong but lightweight and durable applications.

The most serious problem with bioplastics according to Momani is its impact on the food supply. "Since bioplastics are commonly derived from food crops, shortages and price increases could result from scaled up production," he said. We've seen that with corn, which is used not only for human consumption but for animal feed, as well.

Additionally, recycling has caught on and has become a mainstay. While some studies claim that rates are not as high as the industry would like, people are tuned into recycling as part of their lifestyle. To introduce a bioplastic into the mix requires more chemistry. To keep it as a standalone product requires a commercial composting facility, which are few and far between, and altering the mindset that this is a plastic that you don't put into the blue bin. We know how difficult it can be to educate the public.

At the end of the day, despite all of the advantages and disadvantages, Momani adds that the "limiting factor that makes a major shift to bioplastics production impractical is the fact that bioplastics have the mechanical characteristics to replace so few plastics. Even if all bioplastics comparisons to plastics were favorable, their lack of necessary physical properties would severely limit their use. This is the key point that most of the media overlook. All the benefits in the world are irrelevant if the product cannot be used."

Or, I might add, if it can be used in so few applications that it is not profitable to produce. The world turns on new ideas, inventions and innovative thinking, but there are times when the inventor becomes so focused on the "great idea" that he or she fails to see that the law of unintended consequences is always at play. There are pros and cons to everything. Nothing is all good and nothing is all bad. Certainly biodegradability is one small answer to the problem of unmanaged waste. But it is just that—small. Even MHG, in response to a blog I wrote recently about its Florence (Italy) to Singapore expedition to promote biodegradable plastics, noted that "[e]ven if we could operate 300 full-scale commercial plants all over the world, the PHA produced could not replace even 1% of plastics produced every year."

Momani sums it up succinctly by saying that "the disadvantages of bioplastics take away much of their appeal."

You can read Momani's paper here.