The importance of stream slime

24 April 2013

As anyone one who has slipped and fallen into a running stream knows — and that includes me, many times — those rocks aren’t just wet.

They’re slimy.

That coating is called a biofilm. And if there’s start in a riverine food chain, it’s there.

“It’s got bacteria, algae and fungi,” said Emma Rosi-Marshall, a research scientist at the Cary Institute of Ecosystems Studies in Millbrook, N.Y.

Invertebrates feed on the elements in the biofilm. Small fish feed on the invertebrates. Bigger fish, wading birds and mammals feed on those fish. A healthy biofilm means a healthy stream.

But humans may be damaging that biofilm in a way they never thought about — by the drugs they throw away.

Rosi-Marshall is now studying the effects of discarded pharmaceuticals and other substances, including caffeine, on stream ecology.

With colleagues from Indiana University and the University of Loyola in Chicago, Rosi-Marshall studied the effects of six commonly used drugs on streams in New York, Maryland and Indiana.

The drugs included a common antibiotic, ciprofloxacin; and three common antihistamines, including diphenhydramine, which is found in cold and allergy medications like Benadryl.

Rosi-Marshall said that for the past two decades, researchers in Europe and the United States began to discover measurable amounts of hundreds of pharmaceuticals in the water.

In some cases, she said, it’s because people figure the easiest way of getting rid of pills is to flush them down the toilet.

They also get washed into the environment from farms, where antibiotic use for livestock is widespread.

Another source is our urine when we take such drugs. If our bodies don’t metabolize and use all the drugs we take, our kidneys filter them out and they end up in our urine.

It’s also easy to figure out where one of the other drugs Rosi-Marshall studied — caffeine — comes from.

“Think of how many half-filled cups of coffee get thrown down the sink,” she said. “There are all those coffee grounds.”

Rosi-Marshall said that while researchers have been measuring the drugs in the environment, they aren’t sure what their effects might be. The next round of study is trying to find out.

Rosi-Marshall and her team grew biofilm on cellulose tissue — a substance like the leaves that fall into a stream.

When the team had exposed that biofilm to water with the six pharmaceuticals, they saw the respiration rate of the bacteria and fungi slow down — that means they were releasing as much oxygen as usual. The algae’s rates of photosynthesis slowed down as well.

She and her teams also found that the drugs — especially the antihistamines — also altered the biofilm’s colonies of bacteria. Some did better, others worse.

The implications of this study — admittedly in its first stages — is that the drugs we’re releasing into the environment are taking their toll.

Rosi-Marshall said this study and others may indicate that water treatment plants, which now don’t filter out drugs from the water system, get upgrades to address this issue.

It should also make us more aware of what we flush away.

“We tend to forget that when we flush things down the toilet, they don’t disappear,” she said. “They go somewhere.”

This post first appeared in NewsTimes and is republished with permission.

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