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Rx for Action

A blog devoted to helping people find local medicine take-back programs and highlighting current research findings and pending legislation.

Pharmaceuticals change the bottom of the food chain, but not always in the same way

This week saw the publication of a new study into how pharmaceuticals impact the film of bacteria, algae, and fungi that coat stream bottoms. At first glance, the study appears to reveal–at least in part–that chemicals ranging from stimulants to antihistamines have the same impact: a drop in growth. A closer look, though, reveals that this shared drop is itself the result of unique changes happening behind the scenes. And each one could alter the ecosystems these microorganisms call home.

This finding is a part of a larger field study that examined the effects of six diverse pharmaceutical chemicals–alone and in combination–on stream habitats in Indiana, Maryland, and New York. The study focuses on how aquatic biofilms, the communities of bacteria, algae, and fungi that cover rocks and soil, react to these chemicals.

On the list of tested compounds is diphenhydramine, the primary component in Benadryl. As with the other five chemicals, researchers tested the impact of the antihistamine by placing a porous container of the chemical into the stream and waiting for a biofilm to naturally grow around it. The technique revealed that exposure to diphenhydramine hinders the process bacteria use to generate energy needed for growth. The make-up of bacterial communities changed as well. Bacteria species known to break down toxic particles flourished in their new environment, while others fell in number. And in algae, this same pharmaceutical almost completely halted photosynthesis. Taken together, these changes mean that the common antihistamine can actually prevent healthy biofilms from forming on underwater surfaces.

Other pharmaceutical compounds inhibited growth, but not for all the same reasons. Caffeine, for example, altered how well these communities operated, but not what they looked like. Like diphenhydramine, the stimulant made it difficult for bacteria to convert nutrients into energy. But it had no effect on the composition of the communities.

In the end, most of the chemicals tested suppressed biofilms ability to develop and grow. And this shared impact is likely to have repercussions for more than just the microorganisms on stream bottoms. As the base of the food chain, the condition of biofilms says a lot about the health of the ecosystems they support. Because they are the primary food source for invertebrates, which in turn feed fish and other species, biological changes in biofilms can mean change for the entire ecosystem.

It is unclear how much of the impact this study observed is the direct result of the pharmaceuticals. Because the tested biofilms came from real streams and not a lab, the microorganisms were exposed to much more than pharmaceuticals. Additional research is needed to determine how these pharmaceuticals interact with the nutrients and other pollutants that could also be influencing biofilm development.

E. Rosi-Marshall, D.W. Kincaid, H.A. Bechtold, T.V. Royer, M. Rojas, and J.J. Kelly. 2013. Pharmaceuticals suppress algal growth and microbial respiration and alter bacterial communities in stream biofilms. Ecological Applications.

Written by Anjanette Riley, IISG Science Writer.

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Posted by Laura Kammin at 9:45AM on 4/9/2013
Categories: Latest Research