Neither of these bioplastics is widely used, however, because they simply don’t compare to the strength and other properties of traditional plastic, and they cost substantially more. The global plastic market is worth $1.2 trillion, and bioplastics have a market share of $9 billion.

         If bioplastics end up in landfills, they can last for centuries and release methane, a potent greenhouse gas.

While both of the bioplastics now in use can be broken down by microorganisms and become part of the natural world again in a short period of time, this only happens if the plastic is collected and composted in carefully controlled, high-temperature industrial composting facilities — and there aren’t many of those, especially in developing countries where the problem of plastic pollution is most severe.

If bioplastics end up in landfills, as many do, without enough oxygen to break them down, they can last for centuries and release methane, a potent greenhouse gas. If thrown into the environment, they pose threats similar to PET plastic.

“They are basically the same as plastic and don’t decompose in the way most people think they do,” said Rebecca Burgess, CEO of City to Sea, a UK environmental nonprofit that was formed to reduce plastic in the oceans. “They often end up as rubbish littering our streets and oceans and killing marine life. Bioplastics are a ‘false solution’ as they are single use and there are limited options to compost them… Reducing the amount of single-use packaging we use is the only solution.”

The drawbacks of bioplastics to date haven’t stopped marketers like Coca-Cola from implying the plastic pollution problem is being solved. They use the popular, if vague, terms “plant-based” or “bio-based” or “compostable,” for example. “Marketing is highly abusive in this area,” said Taylor Weiss, an assistant professor at Arizona State University who researches algae-based bioplastics.

Even a 100-percent plant-based bottle is not the solution it might seem. Not only can bioplastics find their way into the environment and take many years to break down, but because they are made from plants, they come with the environmental problems that large-scale agriculture causes. The sugars used to make bioplastic often come from transgenic crops sprayed with herbicides and pesticides, and these crops take land out of production that is needed to feed a growing global population. This mirrors the problems found in biofuels, which were similarly seen as an environmental solution. Experts say that using bioplastic and biofuels will greatly increase the land needed for agriculture.