Detecting Soil Contaminants

Biosensors for groundwater monitoring.

Imagine you are sitting in a room by a window on a sunny afternoon in September. You start to feel warm and you want to know the temperature in the room, so you bottle a sample of the air and mail it to a laboratory in another part of the country. Several weeks later, on a snowy October morning, you receive a report telling you what the temperature in the room was on that warm September afternoon. Sound absurd? Sure it does. But this is actually the way most environmental chemical analysis is conducted, bringing the researcher a single, time-delayed measurement that may not accurately reflect the current situation.

Colorado State University chemical engineering Professor Ken Reardon thinks there is a better way. He puts it like this: If you want to know the temperature in the room, you look at a thermometer on the wall – so why not something similar for analysis of groundwater?

Reardon is applying this concept of in situ (in place) continuous measurement to his work in monitoring groundwater for agricultural pesticides. Currently, the primary method for measuring pesticide contamination is to remove a groundwater sample from a well, package it in several sample vials, ship it to a lab to be analyzed by gas or liquid chromatography, and receive the analysis weeks later. Reardon would like to replace laboratory analysis of groundwater with reliable, easy-to-use field sampling methods that produce real-time results.

Reardon and his research team -graduate students Neema Das and Brinson Willis and collaborators Linda Henk, research assistant professor of chemical engineering, and Reagan Waskom, Colorado Extension specialist in soil and crop sciences – are developing unique bio-sensors to detect the presence of agricultural pesticides in groundwater. In a biosensor, a biological component, such as enzymes or whole cells, is fused to the end of a transducer, such as an electrode or optical fiber. When a contaminant is detected by the biosensor, the transducer takes the chemical signal from the biological component and turns it into an electronic signal that can be continuously monitored.

"Continuous groundwater monitoring at the site of pesticide production and use is important for detecting spills and tracking the effectiveness of clean up efforts," Reardon explains. "It's also important from the application end in helping farmers to apply just the amount of pesticide they need and to know where it is going after they put it on their fields. "

So far, Reardon and his colleagues have developed fiber optic biosensors capable of detecting certain chlorinated organic compounds, such as atrazine, at levels as low as one part per billion. No other similar device for inexpensive, continuous, compoundspecific sensing has ever been developed, and Reardon has been issued a provisional patent for his sensor design.

While the developments on this project are very promising, Reardon says the next challenge is to discover appropriate detection systems for additional chemical contaminants.

"What we've got is a start," he says. "What we've found out about pesticides and atrazine we hope to apply to any form of groundwater contamination. The goal of our current research is to make our instruments more effective in analyzing different classes of chemicals. Right now we are working on developing sensors for two other chemicals -alachlor and metalochlor -but obviously there are hundreds more. "

The ultimate goal of Reardon's research is to enable greater agricultural productivity with less environmental impact. While his biosensors may not help us replace the use of pesticides in agriculture, they will ensure that pesticides are used more safely and responsibly. And as companies develop new pesticides that are more environmentally friendly, Reardon and his team will continue to develop more sensors to detect them.