In the Sahara Desert along the coastline in Morocco, more than 300 miles from the nearest city, a green pond now sits in the middle of the sand. It’s a test site for Brilliant Planet, a startup that plans to fight climate change by growing vast quantities of carbon-capturing algae in the world’s deserts.
The way consumers are drinking coffee today — one cup at a time instead of brewing an entire pot — has been evolving as new applications and equipment have been introduced. The trend accelerated and became more complicated once many consumers started working from home because of the pandemic and craving barista-quality coffee.
For environmentally conscious consumers, one such complication was the plastic waste generated by conventional coffee pods. That created demand for such eco-conscious single-serve options like pour-over and tea-bag applications and an opportunity for NuZee Inc., Plano, Texas.
Over one-fifth of all plastic produced worldwide is tossed into uncontrolled dumpsites, burned in open pits or leaked into the environment. In Australia, 1.1 million tonnes of plastic is placed in the market, yet just 16% (179,000 tonnes) is recovered.
To deal with this mounting issue, the Morrison government last week announced A$60 million to fund plastic recycling technologies. The goal is to boost plastic packaging recycling from 16% to 70% by 2025.
It comes after 176 countries, including Australia, last month endorsed a United Nation’s resolution to establish a legally binding treaty by 2024 to end plastic pollution.
This is a good start – more effective recycling and recovery of plastics will go a long way to solve the problem.
But some plastics, particularly agricultural plastics and heavily contaminated packaging, will remain difficult to recycle despite these new efforts. These plastics will end up being burnt or in landfill, or worse, leaking into the environment.
“Biodegradable” plastic is often touted as an environmentally friendly alternative. But depending on the type of plastic, this label can be very misleading and can lead environmentally conscious consumers astray.
What are biodegradable plastics?
Biodegradable plastics are those that can completely break down in the environment, and are a source of carbon for microbes (such as bacteria).
These microbes degrade plastics into much smaller fragments before consuming them, which makes new biomass (cell growth), and releases water, carbon dioxide and, when oxygen is limited, methane.
However, this blanket description encompasses a wide range of products that biodegrade at very different rates and in different environments.
For example, some – such as the bacterially produced “polyhydroxyalkanoates”, used in, for instance, single-use cutlery – will fully biodegrade in natural environments such as seawater, soil and landfill within a few months to years.
Others, like polylactic acid used in coffee cup lids, require more engineered environments to break down, such as an industrial composting environment which has higher temperatures and is rich in microbes.
So while consumers may expect that “compostable” plastics will degrade quickly in their backyard compost bins, this may not be the case.
To add to this confusion, biodegradable plastics actually don’t have to be “bio-based”. This means they don’t have to be derived from renewable carbon sources such as plants.
Some, such as polycaprolactone used in controlled release drug delivery, are synthesised from petroleum-derived materials.
What’s more, bio-based plastics may not always be biodegradable. One example is polyethylene – the largest family of polymers produced globally, widely used in flexible film packaging such as plastic bags. It can be produced from ethanol that comes from cane sugar.
In all material respects, a plastic like this is identical to petroleum-derived polyethylene, including its inability to break down.
Confusion and greenwashing
In 2018, we conducted a survey of 2,518 Australians, representative of the Australian population, with all demographics collected closely matching census data.
We found while there’s a lot of enthusiasm for biodegradable alternatives, there’s also a great deal of confusion over what constitutes a biodegradable plastic.
Consumers have also become increasingly concerned over the practice of “greenwashing” – marketing a product as biodegradable when, in reality, its rate of degradation and the environment in which it will decompose don’t match what the label implies.
So-called “oxo-degradable plastics” are an excellent example of why the issue is so complex and confusing. These plastics are commonly used in films, such as agricultural mulches, packaging and wrapping materials.
Chemically speaking, oxo-degradable plastics are often made from polyethylene or polypropylene, mixed with molecules that initiate degradation such as “metal stearates”.
These initiators cause these plastics to oxidise and break down under the influence of ultraviolet light, and/or heat and oxygen, eventually fragmenting into smaller pieces.
There is, however, some controversy surrounding their fate. Research indicates they can remain as microplastics for long periods, particularly if they’re buried or otherwise protected from the sun.
The new government funding for plastic recycling technologies targets waste that’s notoriously difficult to deal with, such as bread bags and chip packets.
However, this still leaves a substantial stream of waste that’s even more challenging to address. This includes agricultural waste dispersed in the environment such as mulch films, which can be difficult to collect for recycling.
Biodegradable and bio-based plastics have great potential to replace such problematic plastics. But, as they continue to gain market share, the confusion and complexity around biodegradable plastics must be addressed.
For starters, a better understanding of how they impact the environment is needed. It’s also crucial to align consumer expectations with those of manufacturers and producers, and to ensure these plastics are appropriately disposed of and managed at the end of their life.
This is what we’re investigating as part of a new training centre for bioplastics and biocomposites. Our goal over the next five years is to improve knowledge for developing better standards and regulations for certifying, labelling and marketing “green” plastic products.
And with that comes greater opportunity for better education so both plastic producers and people who throw them away really understand these materials. We should be familiar with their strengths, weaknesses and how to dispose of them so we can minimise the damage they inflict on the environment.
Fossil plants reveal the evolution of green life on Earth, but the most abundant samples that are found — fossil leaves — are also the most challenging to identify. A large, open-access visual leaf library provides a new resource to help scientists recognize and classify these leaves.
Researchers found that a projected urban expansion of up to 1.53 million square kilometers over the next three decades threatens the survival of more than 800 species — but also that a focus on urban planning that protects habitats can mitigate the impact.
Students are gaining real-world experience while reducing waste in a new project sponsored by Eastman. The company challenged NC State industrial design seniors in the College of Design to create consumer products with sustainability top of mind.
The students’ design concepts will help Eastman have deeper conversations with consumer brands who want to be more sustainable but may not know exactly how to launch such products. “The goal is to help more brands adopt sustainable materials in order to make a significant impact on the environment,” said Anders Ludvigsen, market development manager at Eastman.
Redwoods, it turns out, have two types of leaves that look different and perform very different tasks. This previously unknown feature helps the trees adapt to both wet and dry conditions – an ability that could be key to their survival in a changing climate.
Just enough water
Wherever trees grow, sooner or later their leaves get wet. For trees in wet environments, this can be a problem if films of water cover their stomata. These tiny pores allow carbon dioxide to enter leaves so the tree can combine it with water to make plant tissue through photosynthesis. Many trees that are common to wet forests have leaves with adaptations that prevent these water films from forming.
For broad-leaved trees like the holm oak, which grows in Mediterranean climates with dry summers and rainy winters, this seasonal wetness challenge is relatively easy to overcome. Their stomata are on the sheltered undersides of their leaves, which keeps them clear of water, while the leaves’ top surfaces absorb water. But redwoods are conifers, or cone-bearing trees, with thin, flat needlelike leaves, and they need a different way to balance the competing goals of repelling and absorbing water.
We knew we wanted to explore how redwoods met the paradoxical challenge of leaf wetness, how much water redwoods could absorb and which leaf features caused differences in water uptake capacity. What we learned came as a total surprise.
Big trees with big secrets
Scientists have long known about redwoods’ ability to absorb water through their leaves. But figuring out how much water redwoods can absorb this way, and how the capacity to do so might vary from one type of climate to another, is a real challenge in this species.
To complicate matters further, gravity is always pushing down on the giant column of water rising upward through a redwood’s trunk. As a result, leaves at the top of the tree always have less available water than those lower down. The treetop’s inherent dryness should pull water into the leaf more quickly than into water-rich leaves at the bottom, just as a dry sponge picks up water faster than a damp one.
For an accurate picture of how redwoods absorbed water, we needed leaves from trees in wet and dry environments, and from multiple heights on those trees. To get them to their natural gravity-based water levels for analysis, we put our leaf samples in a fog chamber – in this case, an ice chest hooked up to a room humidifier – and measured weight gain over time to see how much water they could absorb.
A trail of clues
As we took apart clusters of redwood shoots to immerse them in fog, we divided each cluster into pieces. Redwood shoot clusters fan out from a woody core and are segmented into individual shoots of multiple ages, each with its own set of leaves. We separated shoots along the woody central axis from the much more common pliable shoots on the outer edges of each cluster.
It quickly became obvious that shoots from the center axis had leaves that could absorb water three times faster than peripheral leaves. When we looked inside the leaves with a microscope, we understood that they were two completely different types. They don’t look the same on the outside either, but this was so unexpected that we needed to see their internal structure to really convince ourselves.
The axial leaves were packed with water storage cells, but their phloem – tubes in the leaves that export photosynthetic sugars to the tree – appeared to be blocked and useless. If a tree has leaves, the conventional wisdom is that they are there for photosynthesis, but we wondered whether the axial leaves had a different purpose.
With some additional measurements, we found that redwoods’ axial leaves are specialized for absorbing water. Differences between the surfaces of axial and peripheral leaves, especially their wax coverage, cause the differences in their water absorption rates.
Unlike the axial leaves, redwoods’ peripheral leaves have waxy surfaces with lots of stomata. This helped to explain how they photosynthesize year-round regardless of the long wet season in much of their current habitat.
Further analysis showed that the redwoods’ axial leaves account for only about 5% of the trees’ total leaf area, and barely produce enough energy through photosynthesis to maintain themselves. But they contribute up to 30% of the trees’ total water absorption capacity. Together these two types of leaves balance the dueling requirements of photosynthesis and water absorption, allowing redwoods to thrive in both wet and dry habitats.
Understanding what causes the variation in redwood leaves’ uptake capacity can help us gauge differences in water uptake capabilities among trees and environments, now and in the future. In my opinion, this is the most potentially useful part of our study.
Redwoods vary their two leaf types to suit their local climates. In wet rainforests in the northern part of their range, above Mendocino County, the trees invest in fewer of the axial leaves that are specialized for absorbing water. These leaves are concentrated in the trees’ lower crowns, leaving the photosynthetically high-performing treetops free to maximize sugar production in the bright sun.
In dry forests on the southern margins of redwoods’ range, trees have more axial leaves in their water-stressed tops. This allows them to take better advantage of briefer leaf-wetting events, but it means they photosynthesize less per leaf area than redwoods in wetter areas.
Redwoods’ ability to shift leaf types to match regional climatic differences may help them adjust to climate change in an ever-drier California. That would be good news for conserving these epic trees, and it may be a promising feature to investigate as scientists try to link drought tolerance traits to regional differences among redwood populations.