iSTREEM

iSTREEM models concentrations and spatial distributions of microplastics released from municipal wastewater treatment plants (WWTPs) into riverine systems to support environmental exposure and fate assessment.

Key Features:

• Spatially explicit modeling: Predicts microplastic concentrations across riverine networks in the continental United States and parts of Ontario, Canada.
• WWTP and instream loss parameterization: Simulates a range of WWTP removal efficiencies and instream loss rates used as proxies for net sedimentation processes.
• Ensemble simulation framework: Performs 100 simulations to represent diverse scenarios of microplastic removal and transport dynamics.
• Visualization outputs: Produces heat maps and cumulative distribution outputs summarizing relative concentrations and spatial patterns.
• Scenario analysis with parameter examples: Supports variation of parameters such as instream loss rate (example k = 0.1 d⁻¹; half-life ≈ 7 days) and WWTP removal (example 90% removal with no instream loss).
• Mass transport quantification: Estimates surface water concentrations from specified tonnage inputs and reports mass delivered to downstream estuaries and Great Lakes (example: 8.5% of mass reaching estuaries/Great Lakes under a 90% removal/no-loss scenario).

Scientific Applications:

• Product stewardship and regulatory compliance: Informs evaluation of product emissions and compliance-related exposure assessments for microplastics.
• Assessment of wastewater treatment effectiveness: Quantifies consequences of different WWTP removal efficiencies on downstream microplastic concentrations.
• Risk assessment and spatial prioritization: Identifies spatial patterns of exposure to support risk assessments and prioritization of mitigation efforts.
• Informing management and regulatory strategies: Provides spatially resolved fate information to support development of regulatory frameworks and management practices for aquatic systems.

Methodology:

Spatially explicit in-stream exposure modeling across US and parts of Ontario; simulation of WWTP removal efficiencies and instream loss rates as proxies for net sedimentation; ensemble of 100 simulations; outputs include heat maps and cumulative distributions and allow calculation of surface water concentrations from specified tonnage inputs; example parameterization includes instream loss rate k = 0.1 d⁻¹ (half-life ≈ 7 days).