Article Citation: Baho, D.L., Pomati, F., Leu, E., Hessen, D.O., Moe, S.J., Norberg, J. and L. Nizzetto. 2019. A single pulse of diffuse contaminants alters the size distribution of natural phytoplankton communities. Science of the Total Environment, 638: 578-588. https://doi.org/10.1016/j.sciotenv.2019.05.229
We don’t always think about them much, but the little critters in the food chain are extremely important in keeping our world running. In aquatic systems, these little creatures are often phytoplankton – microscopic algae that are the base food source for all other organisms. Any disruption to that food source could spell trouble for an entire aquatic ecosystem. As a result, some researchers have turned their attention to understanding how emerging contaminants like Pharmaceutical and Personal Care Products affect phytoplankton communities.
Pharmaceutical and Personal Care Products enter the environment mainly through the wastewater stream. Products that humans use are either washed off (shampoos, soaps, lotions, etc.) or not used up completely by our bodies (medication) and find their way down the drain to a wastewater treatment plant, and eventually, back into our rivers, streams, and lakes. As a result, waterbodies often contain a mixture of different PPCPs with compounds like caffeine, ibuprofen, and antibiotics. To understand the impact on the food chain, we have to first ask how phytoplankton are affected by chronic exposure to multiple types of contaminants.
Custom-Built Algae Houses…Filled with Chemicals
Over the course of three weeks in Summer 2016, researchers exposed phytoplankton communities in two lakes near Oslo, Norway to a mix of 12 Pharmaceutical and Personal Care Products. While both lakes were in the same region, Lake Gjersjøen was a mesotrophic lake –it had lower levels of nutrients while Lake Årungen was a eutrophic lake that received agricultural runoff and thus had higher nutrient levels. The phytoplankton used during the experiment were gathered from various depths of each lake to help create a mixed sample that would better represent the lake community. These organisms were then placed into plastic tubing that would allow nutrients to move freely in and out, but not allow the phytoplankton to escape. Researchers chose five different treatment concentrations of Pharmaceutical and Personal Care Product mixtures (i.e. low to high) that were within the range previously measured around other water bodies in Europe. Each bag of plastic tubing was filled with one of the treatment concentrations – exposing the phytoplankton to a pulse of the chemicals until they dissipated into the surrounding water.
Using a custom-built floating rack, researchers completely submerged the experimental set up into the lakes over the course of the 3-week period. This way the researchers created conditions that were as close to normal lake conditions as possible to measure what effects Pharmaceutical and Personal Care Products had on what phytoplankton communities where present and how big they were.
The phytoplankton were sampled both at the beginning and the end of the experiment and ran through a machine to measure how big each phytoplankton cell was.
Small Exposure, Big Effects
After the exposure time, the phytoplankton communities in each lake that were exposed to the two highest concentration levels of Pharmaceutical and Personal Care Products saw shifts in the abundance of larger phytoplankton. Essentially, there were fewer small phytoplankton and more larger ones overall. If you think of a food web, or food chain, the small things get eaten by bigger things. If there are less small phytoplankton that food source decreases for larger organisms, which then decreases the food source for bigger organisms, and so on.
Researchers also found that the type of phytoplankton exposed to the higher treatment levels changed between day zero and the end of the experiment. Both of these results suggest that even a short term exposure to a mixture of Pharmaceutical and Personal Care Products had dramatic effects on the phytoplankton communities in each lake – despite each lake having different levels of nutrients available to the phytoplankton.
Not Acting Alone
Pharmaceutical and Personal Care Products are far from the only stress on aquatic ecosystems – pollution, climate change, development – just to name a few. The results of this study highlight the need to better understand how these contaminants interact with other important stressors. Unfortunately, as our population grows, we will only be adding more and more of these types of chemicals to our environment, creating an increasingly complex exposure cocktail for aquatic organisms. With the health of our aquatic ecosystems at stake, it’s vital that we keep thinking about the little critters and how human-made contaminants may affect them long-term.