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Can biofilms provide a more sensitive measure of pesticide exposure in aquatic ecosystems?

Monitoring the presence and levels of pesticides in Ontario’s aquatic systems is necessary to understand the subsequent impacts on the aquatic environment. Residual concentrations of pesticides are commonly found outside the intended area of application in Ontario’s surface water. The current method used for aquatic monitoring involves the collection and analysis of water samples which can be costly and tedious resulting in irregular water sampling.The provincial government monitors multiple sites across the province.

Lebo Drain, Leamington Ontario. One of the provincial pesticide monitoring sites, and one of my field sites. I took this photo during duckweed bloom mid summer. This site has high pesticide loading.

Whitemans Creek, Brantford Ontario. Another provincial monitoring site. This site has low pesticide loading.


Infrequent and/or poorly coordinated collection of grab samples may not capture the elevated concentrations of pesticides that can occur after a rainfall or irrigation event. This is where alternative sampling methods come in! The use of biofilms as a monitoring tool may provide a more ecologically relevant and integrated measure of pesticide exposure to an aquatic system.


What are biofilms?


Ever walked in a river barefoot and slipped on a slippery rock? That slippery, slimy coating is called a biofilm.

Biofilm coating a rock surface.


Biofilms are a collective of microorganisms that grow on hard surfaces in aquatic ecosystems and have been shown to bioconcentrate pesticides from water, and therefore have the potential to act as a cost-saving, integrated sampling tool to monitor pesticide exposures in aquatic ecosystems.

Biofilms also form the base of the aquatic food web by acting as a fundamental dietary component for fish, tadpoles, and invertebrates. Existing water quality guidelines for acceptable pesticide levels do not consider the exposure pathway where aquatic organisms consume contaminated food. Therefore, current ecotoxicological risk assessments may be underestimating the potential risk of pesticide contaminants to non-target aquatic organisms. Understanding the potential for biofilms to characterize pesticide exposure is critical to effectively assess their use as a monitoring tool.


In a follow up study I fed biofilms contaminated with pesticides to the mayfly species Neocloeon triangulifer. These organisms are sensitive to pesticide-contaminated food! Pictured above: assessing mortality in N. triangulifer.


How can we sample biofilms?


Since biofilms are ubiquitous, collected a sample of biofilm can be a simple as going to your river or water body of choice and scraping the biofilm off the rocks and substrate found in that ecosystem. However, this may not be the best choice of sampling if we want to compare samples across different sites: we need to standardize our biofilm sampling methodology. We can use something called a periphytometer (this is just a fancy name for a sampling device which measures biofilm).


Example of a periphytometer set up at one of our field sites. We will put out multiple periphytometers at each site to make sure we get enough sample (sometimes equipment goes missing when left unattended in the field!)

Birds-eye view of two periphytometers. Red buoys are attached to make sure they stay at a constant depth as the river depth fluctuates during the summer.


In my project, we built periphytometers that contain acrylic slides. These slides act as a uniform substrate for the biofilm communities to colonize. We leave them in the water for about 8 weeks, and then collect the biofilm. These sampling devices can allow us to standardize depth, light availability and water flow, and hopefully can provide a more representative sample of biofilm in the water body of interest.


Admiring a biofilm 'crop' on one of the acrylic slides. This slide took 8 weeks to colonize. Typically we will need at least 15 of these slides to get enough mass for one sample.


A preliminary assessment of the data suggests that both types of biofilms detected a broader range of pesticides compared to those detected in water samples obtained from the same sites. It appears that the current water sampling method is not fully characterizing the pesticide exposure in Ontario’s aquatic systems. The development of a novel, cost-effective and more sensitive sampling tool would be beneficial for provincial monitoring programs.


Written by Moira Ijzerman.







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