Waterways as drug couriers

Posted on March 10, 2014

A wide range of pharmaceutical compounds have been detected in freshwater systems. While concentrations of such chemicals are normally very low, they can be much higher in streams receiving industrial effluent. Organic biofilms – slimy layers of algae, fungi, bacteria and organic matter that develop on submerged surfaces – are at the interface of the inorganic and living environment and help to support the stream food web, but the influence of dissolved pharmaceuticals on stream biofilms has only just been investigated. American scientists measured the effects of six common pharmaceutical pollutants (a stimulant, an antibiotic, an antidiabetic / cholesterol reducer, and three antihistamines) on the structure and function of biofilms in rural and suburban waterways in New York, Indiana and Maryland. The researchers created chemical-diffusing substrates by filling plastic cups with agar solution containing one of the test pharmaceuticals at a concentration of 0.012-0.015 mol / L. Each cup was capped with a porous substrate: either fritted glass (to encourage algal colonisation) or cellulose sponge (to encourage bacterial and fungal colonisation). Two other treatments – controls, with no pharmaceuticals, and mixtures, with all compounds combined – were also prepared. The cups were fixed to the stream bed and retrieved after 18 days. Assays showed that chemical diffusion from the cups occurred throughout the whole period. Incubation of the substrates under light and dark conditions permitted the measurement of community respiration, primary production and chlorophyll content. Respiration was significantly reduced (by 49-97%) in the presence of four of the compounds and the mixture, which also lowered primary production and chlorophyll content to a significant extent. One of the antihistamines (diphenhydramine) reduced primary production by 99.8%. This compound also reduced the prevalence in the biofilms of Flavobacteria, a widely-distributed gram-negative bacterium. The suppression of bacteria, algae, primary production and community respiration suggests that pollutant pharmaceuticals can pose a risk to stream biofilms and ecosystems.

Reference: Rosi-Marshall, E.J. et al. (2013). Pharmaceuticals suppress algal growth and microbial respiration and alter bacterial communities in stream biofilms. Ecological Applications 23(3), 583–593. http://www.esajournals.org/doi/pdf/10.1890/12-0491.1