‘Science’ Category

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A white fleck of plastic is engulfed by a coral polyp.Source: Alex Seymour, Duke Univ.

Scientists have long known that marine animals mistakenly eat plastic debris because the tiny bits of floating plastic might look like prey. But a new Duke University study of plastic ingestion by corals suggests there may be an additional reason for the potentially harmful behaviour. Visual cues, such as a resemblance to prey, don’t factor into the appeal, the researchers noted, because corals have no eyes.

This new study suggests there may be an additional reason for the potentially harmful behaviour: The plastic just plain tastes good.

“Corals in our experiments ate all types of plastics but preferred unfouled microplastics by a threefold difference over microplastics covered in bacteria”, said Austin S. Allen, a PhD student at Duke’s Nicholas School of the Environment. “This suggests the plastic itself contains something that makes it tasty.”

“When plastic comes from the factory, it has hundreds of chemical additives on it. Any one of these chemicals or a combination of them could be acting as a stimulant that makes plastic appealing to corals”, said Alexander C. Seymour, a geographic information systems analyst at Duke’s Marine Robotics and Remote Sensing Centre, who co-led the study with Allen.

Further research will be needed to identify the specific additives that make the plastic so tasty to corals and determine if the same chemicals act as feeding stimulants to other marine species.

Microplastics, tiny pieces of weathered plastic less than 5 millimetres in diameter, began accumulating in the oceans four decades ago and are now ubiquitous in the marine environment. They pose a major threat to foraging sea animals, including many species of birds, turtles, fish, marine mammals and invertebrates.

Because plastic is largely indigestible, it can lead to intestinal blockages, create a false sense of fullness or reduce energy reserves in animals that consume it. “About eight percent of the plastic that coral polyps in our study ingested was still stuck in their guts after 24 hours”, said Allen.

It can also leach hundreds of chemical compounds into their bodies and the surrounding environment. The biological effects of most of these compounds are still unknown, but some, such as phthalates, are confirmed environmental estrogens and androgens – hormones that affect sex determination.

Allen and Seymour conducted their two-part study using corals collected from waters off the North Carolina coast. In their first experiment, they offered small amounts of eight different types of microplastics to the corals to see if the animals would eat the bite-sized bits versus other similarly sized items offered to them, such as clean sand.

“We found that the corals ate all of the plastic types we offered and mostly ignored sand”, Allen said.

In the second experiment, they put groups of coral into separate feeding chambers. Each group was offered the same amount of “food” — weathered plastics — for a 30-minute period, but some groups got only particles of unfouled microplastics while others got only particles of weathered microplastics fouled with a bacterial biofilm. This experiment verified that the corals would eat both types of plastic, but preferred the clean type by a three-to-one margin.

The researchers hope their findings will encourage scientists to explore the role taste plays in determining why marine organisms ingest microplastics.

“Ultimately, the hope is that if we can manufacture plastic so it unintentionally tastes good to these animals, we might also be able to manufacture it so it intentionally tastes bad”, Seymour said. “That could significantly help reduce the threat these microplastics pose.”

Allen and Seymour’s peer-reviewed study was published October 23, 2017 in the online edition of journal Marine Pollution Bulletin. You can access the study free of charge until December 10, 2017 by clicking here.

Daniel Rittschof, Norman L. Christensen Professor of Environmental Sciences at Duke’s Nicholas School, co-authored the new paper. Funding for the research came from the Oak Foundation. Allen and Seymour both earned Master of Environmental Management degrees from the Nicholas School in 2016.

CITATION: “Chemoreception Drives Plastic Consumption in a Hard Coral,” Austin S. Allen, Alexander C. Seymour, Daniel Rittschof, Marine Pollution Bulletin, Oct. 23, 2017. DOI: 10.1016/j.marpolbul.2017.07.030

Muddied waterI have no problem with the idea of recycling sewage water to enable us to drink it. There is technology available that brings us fairly close to a product that is safe to drink. Science will find a solution to the remaining problems. Eventually.

In the meantime the following information shows there is plenty of concern to muddy the waters of the concept of recycling previously muddied water to enable us to drink it.

There is concern not just with the science but also with the governance of the procedures required to maintain a safe drinking standard, especially when that standard is not clearly defined.

There is an Australian Drinking Water Guideline (ADWG) that is produced by the National Health and Medical Research Council (NHMRC). The most recent edition being ADWG6 [1] produced in 2011. However it is lacking clear guidelines in several areas, some of which are:

  • Escherichia coli (E. coli) – “No guideline value has been set for pathogenic Escherichia coli and its inclusion in routine monitoring programs is not recommended.”
  • Bacteroides – “No guideline value has been established for Bacteroides in drinking water”
  • Clostridium perfringens – “No guideline value has been set for Clostridium perfringens in drinking water.”
  • Total coliforms – Total coliform bacteria (excluding E. coli) – “No guideline value has been set for total coliforms in drinking water”
  • Helicobacter pylori – “No guideline value has been set for Helicobacter pylori in drinking water and its inclusion in routine monitoring programs is not recommended.”
  • Oestrogenic hormones [2] – The ADWG6 does not contain a guideline for this.

These are just a few examples, references to chemicals and other compounds not included, of what could be found in recycled sewage water and the attached guideline value. If no guideline is given by the NHMRC in a document as important as the Australian Drinking Water Guideline, then that perhaps leaves it up to the local management of the various water suppliers to determine what may or may not be safe and this is just one area where I believe we have a problem.

2008 saw the completion of the Western Corridor Recycled Water Scheme in SE Queensland. It was designed to provide water for industrial, agricultural use and also to supplement the drinking water supplies in the nearby Wivenhoe Dam. Producing in excess of 200 million litres of purified water per day it is currently only used for the Swanbank, Tarong and Tarong North power stations. In November 2008 the Queensland Premier, Anna Bligh, declared that unless dam levels dropped below 40% capacity the recycled water would not enter the dam.[3]

Adelaide scientist Professor Don Bursill, who developed Australia’s drinking water guidelines, has stated that he would not drink recycled sewage and would not back its use.[4] Professor Bursill who was recognised in Australia Day honours for his contribution to water quality research says the technology that would make recycled sewage suitable for drinking already exists, but he is not confident we have the back-up systems to ensure it stays safe.

“You can turn anything wet into drinking water if you have enough money,” he said. “To really ensure it is safe would cost a tremendous amount. This is one bloke who isn’t going to drink it.”

Professor Bursill, who in retirement is the chairman of the Torrens Taskforce, says while it is possible to produce safe drinking water from waste water, present systems are not adequate to cover the risk of bacterial contamination.

Conversely: Professor Steven Oppenheimer, Director of the Centre of Cancer and Development Biology, California State Northbridge University in an article titled “Augmenting Drinking Water with Reclaimed Water”[5] has stated “The United States of America, and for that matter, the world’s scientific community does not and will not know all of the toxic agents and carcinogens that may be able to make it through the indirect reclaimed water process. …Imagine the possibility of thousands of unknown agents getting into our water supply as a result of hospital and industrial waste releases. And the release by such organizations will not be predictable. We do not even have tests available to determine many of the unknowns that may show up in water from the indirect water reuse program.”[5]

So when it comes to a tap near you, will you trust the authorities to have it right?