POCIS Calibration for Organic Compound Sampling in Small Headwater Streams

Area of Science:

• Environmental Chemistry
• Water Quality Monitoring
• Environmental Toxicology

Background:

• Atrazine is a widely used herbicide, and its presence in headwater streams necessitates accurate monitoring.
• The polar organic chemical integrative sampler (POCIS) is a passive sampling technique used for assessing contaminant levels in aquatic environments.

Purpose of the Study:

• To determine field-based atrazine sampling rates (Rs) using the POCIS method in headwater streams.
• To evaluate the performance of a mechanistic model for predicting POCIS sampling rates.
• To assess factors influencing POCIS sampling efficiency, including flow velocity and temperature.

Main Methods:

• Conducted field sampling over three years in nine headwater streams, with multiple exposure periods per site per year.
• Measured atrazine concentrations using the POCIS method and analyzed sampling rates (Rs).
• Assessed POCIS performance by measuring alabaster dissolution rates and developed a mechanistic model incorporating flow and temperature effects.

Main Results:

• Field-based atrazine sampling rates (Rs) were consistently measured at approximately 148 mL/d, with a standard deviation of 0.17 log units (factor 1.5).
• POCIS canisters were found to reduce mass transfer coefficients by a factor of two.
• A mechanistic model provided a fair estimate of the effective exchange surface area (12.5 ± 0.8 cm²), though its accuracy was limited at low flow velocities (<1 cm/s).

Conclusions:

• The atrazine sampling rate of 148 mL/d using POCIS provided consistent results across nine headwater streams over three years.
• Sorbent distribution and chemical analysis were identified as minor sources of error in the sampling process.
• The study confirmed the reliability of the POCIS method for long-term, low-level monitoring of atrazine in headwater streams.