Deposit schemes reduce drink containers in the ocean by 40%

Uncountable numbers of drink containers end up in the ocean every year.
Shutterstock

Qamar Schuyler, CSIRO; Britta Denise Hardesty, CSIRO, and Chris Wilcox, CSIRO

Plastic waste in the ocean is a global problem; some eight million metric tonnes of plastic ends up in the ocean every year.

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Eight million tonnes of plastic are going into the ocean each year

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One possible solution – paying a small amount for returned drink containers – has been consistently opposed by the beverage industry for many years. But for the first time our research, published in Marine Policy, has found that container deposits reduce the amount of beverage containers on the coasts of both the United States and Australia by 40%.

What’s more, the reduction is even more pronounced in areas of lower socio-economic status, where plastic waste is most common.

Plastic not so fantastic

There have been many suggestions for how to reduce marine debris. Some promote reducing plastic packaging, re-purposing plastic debris], or cleaning beaches. There has been a push to get rid of plastic straws, and even Queen Elizabeth II has banned single use plastics from Royal Estates! All of these contribute to the reduction of plastics, and are important options to consider.

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Legislation and policy are another way to address the problems of plastic pollution. Recent legislation includes plastic bag bans and microbead bans. Economic incentives, such as container deposits, have attracted substantial attention in countries around the world.

Several Australian jusrisdictions, including South Australia, the Northern Territory, and New South Wales), already have container deposit laws, with Western Australia and Queensland set to start in 2019. In the United States, 10 states have implemented container deposit schemes.

But how effective is a cash for containers program? While there is evidence to suggest that container deposits increase return rates and decrease litter, until now there has been no study asking whether they also reduce the sources of debris entering the oceans.

In Australia, we analysed data from litter surveys by Keep South Australia Beautiful, and Keep Australia Beautiful. In the US, we accessed data from the Ocean Conservancy’s International Coastal Cleanup.

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We compared coastline surveys in states with a container deposit scheme to those without. In both Australia and the US, the proportion of beverage containers in states without a deposit scheme was about 1.6 times higher than their neighbours. Based on estimates of debris loading on US beaches that we conducted previously, if all coastal states in the United States implemented deposit schemes, there would be 6.6 million fewer containers on the shoreline each year.

Keep your lid on

But how do we know that this difference is caused by the deposit scheme? Maybe people in states with container deposit schemes simply drink fewer bottled beverages than people states without them, and so there are fewer containers in the litter stream?

To answer that question, we measured the ratio of lids to containers from the same surveys. Lids are manufactured in equal proportion to containers, and arrive to the consumer on the containers, but do not attract a deposit in either country.

If deposit schemes cause a decrease in containers in the environment, it is unlikely to cause a similar decrease in littered lids. So, if a cashback incentive is responsible for the significantly lower containers on the shorelines, we would expect to see a higher ratio of lids to containers in states with these programs, as compared to states without.

That’s exactly what we found.

We were also interested in whether other factors also influenced the amount of containers in the environment. We tested whether the socio-economic status of the area (as defined by data from the Australian census) was related to more containers in the environment. Generally, we found fewer containers in the environment in wealthier communities. However, the presence of a container deposit reduced the container load more in poorer communities.

This is possibly because a relatively small reward of 10 cents per bottle may make a bigger difference to less affluent people than to more wealthy consumers. This pattern is very positive, as it means that cashback programs have a stronger impact in areas of lower economic advantage, which are also the places with the biggest litter problems.

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Ultimately, our best hope of addressing the plastic pollution problem will be through a range of approaches. These will include bottom-up grassroots governance, state and federal legislation, and both hard and soft law.

Along with these strategies, we must see a shift in the type of we products use and their design. Both consumers and manufacturers are responsibility for shifting from a make, use, dispose culture to a make, reuse, repurpose, and recycle culture, also known as a circular economy.

Qamar Schuyler, Research Scientist, Oceans and Atmospheres, CSIRO; Britta Denise Hardesty, Principal Research Scientist, Oceans and Atmosphere Flagship, CSIRO, and Chris Wilcox, Senior Research Scientist, CSIRO

This article was originally published on The Conversation. Read the original article.

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Sizes matters for black hole formation, but there’s something missing in the middle ground

An artist’s impression of a supermassive black hole at the centre of a galaxy.
NASA/JPL-Caltech

Holger Baumgardt, The University of Queensland and Michael Drinkwater, The University of Queensland

So far, all black holes discovered by astronomers fall into two broad categories: “stellar mass” black holes and “supermassive” black holes.

But what puzzles astronomers is why the two extremes – what about intermediate-sized black holes?

Black holes were predicted by Albert Einstein’s general theory of relativity. Their gravity is so strong that no material object, not even light, can escape from their vicinity.

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Astronomers have only been able to obtain evidence for their existence in recent decades by studying black holes accreting (attracting) gas from nearby stars and finding fast-moving stars in the vicinity of black holes.

But since 2015 an exciting third way to detect black holes has become available: gravitational waves from merging black holes.

From one extreme…

Stellar mass black holes can have masses between a few to a few tens of solar masses – the mass of our Sun. They are thought to form at the end of the lives of massive stars. When these stars run out of gas from which to produce energy, they leave behind massive remnants that can only collapse into black holes.

So far, astronomers have discovered a dozen stellar mass black hole candidates in the Milky Way, most of which accrete matter from nearby companion stars.

They also detected gravitational waves from several merging stellar mass black hole pairs in distant galaxies.

It’s estimated that our Milky Way alone should contain about 100 million stellar mass black holes, most of which do not have close companions from which they can accrete matter, and which therefore stay invisible.

… to the other

At the other end of the mass scale are what astronomers call supermassive black holes. These are about a million to a few billion times more massive than our Sun.

Astronomers think that almost every large galaxy contains a supermassive black hole at its centre.

The Milky Way, for example, contains a black hole of about 4 million solar masses, called Sagittarius A* (Sgr A*), in its centre. Astronomers can study this black hole by looking at the motion of stars that are close to Sgr A* and are flung through space by the huge gravitational attraction of the black hole.

Is that a supermassive black hole?

Although astronomers have gained a good understanding of the distribution and masses of supermassive black holes in galaxies in the nearby universe, they still do not know where supermassive black holes come from.

Observations show that some supermassive black holes already existed and were actively accreting gas from their surroundings when the universe was just a few hundred million years old.

A composite x-ray and infrared image of the supermassive black hole Sagittarius A* at the centre of the Milky Way.
NASA/UMass/D.Wang et al., IR: NASA/STScI

In 2011 a team of astronomers said they had found evidence of a supermassive black hole that existed only 770 million years after the Big Bang. Then, last month, another team of astronomers revealed what they think could be evidence of a supermassive black hole from when the universe was only 690 million years old.

This creates a problem for theories that assume that supermassive black holes grew out of the stellar-mass black holes left behind by the first generation of stars in the early universe.

There is not enough time for these black holes to have grown to reach the huge masses that we can see in observations of the first galaxies.

The middle ground for black holes

An alternative theory is that supermassive black holes form from so-called intermediate-mass black holes. These hypothetical black holes could have masses from a few hundred to a few hundred thousand solar masses.

Starting more massive, supermassive black holes would need less time to grow to their present sizes. They could also accrete mass more efficiently since the maximum amount of mass that a black hole can accrete is directly proportional to its size.

Intermediate mass black holes could form out of the collapse of very massive stars that might have existed in the very early universe.

Nowadays stars form with an upper mass limit of at most a few 100 solar masses. Conditions in the very early universe might have been more favourable towards building more massive stars and might have allowed the formation of stars of a few thousand or maybe even up to a million times the mass of our sun.

This chart illustrates the relative masses of stellar black holes and supermassive black holes, and the mystery of the intermediate-mass black holes, with masses up to more than 100,000 times that of our sun, remains unsolved.
NASA/JPL-Caltech (edited)

The hunt is on

Astronomers are currently searching for intermediate mass black holes and there are a few potential candidates. Like their more massive cousins they could reveal their existence by accreting material from nearby stars or by the fast motion of nearby stars.

A prime place to look for intermediate mass black holes could be globular clusters, dense clusters of a few hundred thousand of stars to a few million of stars.

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Like supermassive black holes, globular clusters are old and are among the first objects which have formed in the universe.

Astronomers – including at the University of Queensland – recently found evidence that such an intermediate mass black hole with about 2,200 times the mass of our Sun could exist at the centre of the globular cluster 47 Tucanae.

They did this by studying the acceleration of pulsars (compact remnants of dead stars that formed with about 20 times the mass of our Sun) in the globular cluster.

If more of these can be found, they might provide the missing link between stellar mass and supermassive black holes and could shed light on how supermassive black holes have formed.

Holger Baumgardt, Associate Professor, The University of Queensland and Michael Drinkwater, Professor of Astrophysics, The University of Queensland

This article was originally published on The Conversation. Read the original article.