What’s New at the Lab: New Samplers for Surface Water Monitoring

By
Daniel D. Snow, Ph.D., UNL Water Sciences Laboratory
Shannon Bartelt-Hunt, Ph.D., UNL Department of Civil Engineering

Collection of representative samples from a flowing stream presents a number of interesting challenges, especially when monitoring for low concentrations of pesticides, pharmaceuticals or steroid hormones.

While traditional grab and composite sampling can tell us about the occurrence of contaminants in surface waters, these techniques only capture information at the time of collection. Individual and composite samples cannot easily characterize concentration changes during changing flow, sources, and the influence of precipitation.  Continuous on-line sampling, where hundreds of samples are collected and analyzed, may be prohibitively expensive.

A new type of sampler developed by the U.S. Geological Survey for use in monitoring trace organic chemicals is the Polar Organic Chemical Integrative Sampler (POCIS).  This device is designed to trap polar (water soluble) organic compounds from water, and is comprised of a solid sorbent sandwiched between two filter membranes.  Multiple POCIS can be deployed in a single cage for replicate measurements of the constituents of interest.  These samplers are anchored at different locations on a stream, left to trap contaminants, retrieved and analyzed in the laboratory. Its ease of use and apparent resistance to fouling make it particularly attractive for determining time-weighted average concentrations of organic compounds in water.

POCIS samplers have been used by researchers in Nebraska for both qualitative and semi-quantitative estimate of pharmaceutical, pesticide and hormone occurrence in surface waters.  
POCIS are passive samplers, meaning that no additional flow measurements are required to obtain estimates of time-weighted average concentrations.  Average concentrations can be estimated based upon an uptake rate for a given compound.

Although these uptake rates are ideally constant over a range of environmental conditions, recent studies suggest uptake rates are highly dependant on temperature, salinity, other dissolved organics, and membrane fouling.  Currently, we are working to understand how these factors influence the contaminant concentrations predicted by POCIS.

Another promising technology for improved sampling organic contaminants is the development of a more selective sorbent, perhaps using customized polymers or antibodies. Research is now underway at UNL to determine the best sampling approach for increasing our understanding the occurrence, fate and effects of these compounds in our water supplies.