Monitoring, Ecological Risk Assessment, and Management of Microplastics in the  Laurentian Great Lakes

Plastics are a diverse and ubiquitous group of materials that have seen a surge in production in the past century. The widespread use of plastics coupled with unsustainable materials management has led to plastic pollution, including the ubiquity of microplastics across the globe. Microplastics are generally understood to be smaller plastic particles, from 1 micrometer (μm) to 5 mm in size, that are diverse in their physical and chemical characteristics. Microplastics originate from industrial sources, the wear and tear of plastics during use (e.g., clothing, tires, paint), and from the breakdown of discarded plastic products in the environment. Research has shown that microplastics can have adverse effects on aquatic organisms.  

This report outlines the results and deliverables from an International Joint Commission (IJC) Great Lakes Science Advisory Board (SAB) Work Group focused on microplastics in the Laurentian Great Lakes (hereafter called the Great Lakes), whose objectives were to:

1. Synthesize recent advances and knowledge in microplastic science relevant to the Great Lakes. 
2. Develop a framework for monitoring microplastics that would enable harmonized monitoring and reporting across the Great Lakes region. 
3. Advance a coordinated risk assessment and management framework for microplastic in the Great Lakes focused on ecological effects that would contextualize the results of a monitoring program.

The Great Lakes and their watersheds are home to much of North America’s freshwater resources and a range of aquatic species of ecological, commercial and cultural importance. The Great Lakes Water Quality Agreement (GLWQA), established by the Governments of the United States and Canada (the Parties), is meant to help prevent and resolve issues threatening ecosystem health and water quality within the transboundary waters of the Great Lakes. Under Annex 10 of the GLWQA, the US and Canada monitor multiple indicators to assess the health of the Great Lakes ecosystem. To inform how microplastics could be included as a sub-indicator under the GLWQA framework, the IJC SAB convened a Work Group to synthesize recent advances in microplastic knowledge relevant to the Great Lakes and develop separate but coordinated microplastics monitoring and ecological risk assessment and management frameworks. 

The objectives were successfully addressed through the following activities. The Work Group synthesized knowledge on the environmental occurrence of microplastics in the Great Lakes basin based on a review of published literature only, as no basin-wide, coordinated monitoring programs for microplastics currently exist. Work Group members held a session on microplastics at the 2023 Annual Conference of the International Association for Great Lakes Research (IAGLR). Data on the ecological effects of microplastics on aquatic organisms of relevance to the Great Lakes were reviewed and used to update the Toxicity of Microplastics Explorer (i.e., ToMEx 2.0, available early 2025) database.

The Work Group organized two expert workshops. The first was held in September 2023 in Ann Arbor, MI and advanced a harmonized monitoring framework for microplastics through the development of standardized operating procedures for collecting water, sediment and biota for microplastics analyses. The second workshop was held in January 2024 in Windsor, ON and advanced a coordinated ecological risk assessment and management framework. Key findings about microplastics in the Great Lakes are listed below as well as tools developed by the Work Group (listed as project outcomes). Recommendations identified through these efforts are also presented below.

Key Findings

• Microplastics are ubiquitous in all environmental media (e.g., water, sediment, biota, and beaches) in the Great Lakes basin, and they are especially concentrated in more populated systems such as Lakes Michigan and Ontario. Microplastics are a diverse group of contaminants with varied shapes, sizes, and chemical compositions found in these matrices, making them challenging to measure and understand. 
• Reconnaissance-level sampling for microplastics has been performed in the Great Lakes, but many questions remain about spatial and temporal variability, transport, sources and mitigation. Moreover, most of this data has been collected in a non-harmonized manner, as there is no basinwide, coordinated monitoring program for microplastics in the Great Lakes region. 
• Existing studies measuring microplastics in the Great Lakes use highly varied sampling and analysis protocols. The lack of harmonized methods for sample collection and analysis, as well as reporting guidelines, applied to date limits current abilities to assess the status and trends of microplastics in the region. 
• Microplastics are reported to be present in sources of drinking water and in fish collected from the Great Lakes and their watersheds. For fish, these levels are among the highest reported worldwide. This suggests human exposure to microplastics through Great Lakes resources. 
• The peer-reviewed literature includes a growing number of laboratory toxicity tests that assess the impacts of microplastics on aquatic species. These studies have found that microplastics, including at environmentally relevant concentrations, can affect aquatic organisms relevant to the Great Lakes. 
• Sufficient research on the ecological effects of microplastics enabled us to derive preliminary risk thresholds for ambient (surface) water using a species sensitivity distribution (SSD) approach. More data are still needed for sediments to populate robust SSDs and derive risk thresholds with confidence. The process followed approaches used by other groups and forms the basis for an ecological risk assessment framework for the Great Lakes.
• Experts in ecotoxicology and risk assessment expressed that risk thresholds should be derived from robust SSDs and expressed confidence in the approach used by the Work Group to develop an ecological risk assessment framework. 
• Applying preliminary risk thresholds reveals that some ambient water samples from the Great Lakes have concentrations of microplastics that already exceed risk thresholds of ecological concern.

Project Outputs 

Combined, the deliverables of this IJC SAB Work Group present the tools needed to monitor microplastics and assess their statuses and trends over time in the Great Lakes and their watersheds. These tools have been created to align with relevant frameworks, such as the State of the Great Lakes (SOGL) reports, and thus can be adopted by monitoring and management agencies for use with minimal adaptation. These tools have also been created in such a way that allows for iterative improvements as we increase knowledge, for example, on risk and/or local microplastic characteristics, or as program needs change.

1.  An updated literature review of microplastics in the Great Lakes, including a proposed standard definition, field and lab measurement methods, environmental occurrence data, toxicity data for freshwater species, and regional policy and management considerations (Supplemental Materials A). 
2. A proposed definition of microplastics as: “solid polymeric materials to which chemical additives or other substances may have been added, which are particles greater than 1 μm and less than 5,000 μm in all three dimensions. Polymers that are derived in nature that have not been chemically modified (other than by hydrolysis) are excluded.” This definition aligns with the definition recently adopted in the State of California. 
3. An updated publicly accessible database on measured concentrations of microplastics in various matrices across the Great Lakes basin (up to March, 2023; Dataverse Link). 
4. An updated database on microplastics toxicity data available on an open-access platform that can be used to generate SSDs (up to January, 2023; Toxicity of Microplastics Explorer 2.0). 
5. Standard Operating Procedures (SOPs) with reporting guidelines for sampling microplastics in lake water, tributary water, sediment, and biota (Supplemental Materials C). Several of these SOPs were available from a previous working group convened by the Southern California Coastal Water Research Project (SCCWRP) Authority and amendments have been proposed as appropriate for their use in the Great Lakes. These SOPs can be tailored to meet specific monitoring requirements and data objectives for each matrix. 
6. A coordinated ecological risk assessment and management framework for microplastics in ambient water and sediment, adapted to align with the SOGL reporting framework and locally relevant guidelines (Supplemental Materials D).

Recommendations 

• The Parties should include microplastics as a Toxic Chemicals sub-indicator for the triennial SOGL reports under Annex 10 of the GLWQA and consider microplastics for inclusion as a Chemical of Mutual Concern (CMC) under Annex 3 of the GLWQA to support the development and implementation of a coordinated action plan for reducing microplastic pollution in the Great Lakes. 
• The Parties should create and implement a basin-wide, coordinated monitoring program for microplastics in the Great Lakes (in lake and tributary water, sediment and biota) that includes harmonization of field and lab methods among federal, state, provincial, local and Indigenous agencies. Such monitoring is critical for quantifying microplastic sources and emissions and understanding their transport and fate in the Great Lakes and its watershed to inform ecological risk assessments, mitigation and management strategies for microplastics. This program would benefit from the SOPs and reporting guidelines adopted and adapted by the Work Group. Importantly, in addition to total counts or concentrations, the following microplastic characteristics should be reported to facilitate comparison across studies:
  • Morphology, as percent of total 
  • Polymer type (if identified), as percent of total 
  • Size range assessed, based on field and lab methods 
  • Size fractions (if distinguished), as percent of total
• Given the persistence and ubiquity of microplastics, the Parties should implement measures to prevent the emissions of plastic pollution to the Great Lakes watershed to reduce environmental concentrations and prevent further ecological risk. 
• The Parties should support research that improves our monitoring and analytical capabilities (i.e., improving methods for better detection and characterization of microplastics) and expands our understanding of the toxicity of microplastics to species relevant to the Great Lakes watershed to collectively increase our ability to assess exposures and ecological risks. Supporting additional research into the effects of sediment exposures will address an important knowledge gap in microplastic toxicity.

The above is taken from the Executive Summary of the “Final Report of the IJC Great Lakes Science Advisory Board Work Group on Microplastics” submitted to the International Joint Commission by the Great Lakes Science Advisory Board and published in November 2024. Click here to read the full report.

CGLR’s business and sustainability network programming is supported by the Fred and Barbara Erb Family Foundation.