Enzyme-Based Reductase Could Replace Cadmium in Nitrate Testing

After decades of using the toxic, heavy-metal cadmium in standard and widely applied colorimetric methods for determining nitrate in water, scientists at the United States Geological Survey are evaluating a new cadmium-free nitrate test developed by Michigan-based Nitrate Elimination Co. Inc. (NECi).

The USGS study is the first controlled, scientific validation of NECi’s enzyme-based alternative to cadmium-based reagents. The method was to enter production at USGS in January 2006 with publication in a peer-reviewed journal to follow later in the year.

“Our method provides a way to do nitrate testing without risk to the user or the environment,” said NECi president Dr. Bill Campbell, biochemist and emeritus professor at Michigan Tech University.

The USGS results demonstrate that NECi’s biotechnologically engineered enzyme, called NaR, has the potential to replace cadmium in millions of nitrate detection tests performed annually by water suppliers, wastewater treatment facilities, and laboratories around the globe, Campbell said.

Hach Company, a global supplier of water testing reagents, likewise sees opportunity.

USGS chemists Charles Patton, Colleen Gupta, and Jennifer Kryskalla have applied enzyme-based reagents from Nitrate Elimination Company to replace cadmium in determination of nitrate. (USGS photo)

“Testing water samples for nitrate is one of the industry’s most common laboratory procedures,” said Hach’s Jason Butchko, business unit manager for lab automation. “Through our evaluation of NECi’s enzymatic nitrate reductase, we’ve found that the method looks promising as a green alternative to the traditional method.”

Cadmium, a key reagent in the most widely used nitrate tests, can adversely affect laboratory personnel who handle it and can cause harm to the environment through improper disposal.

Most labs already have the equipment needed to conduct tests with the new enzyme; USGS research was performed with air-segmented continuous flow analyzers, time honored, automated colorimetric analysis workhorses that are easy to adapt for use with a soluble enzymatic reducing reagent.

The NaR method can also be used on high-performance, discrete analyzer (DA) platforms. Automatic discrete analyzers perform the same routine, colorimetric determinations that continuous flow analyzers do, but with substantially reduced sample and reagent volumes and with much less operator intervention and maintenance.

Dr. Charles Patton, an analytical chemist with the USGS, values the high level of automation and productivity afforded by DA technology, but notes that traditional granular cadmium reactors, which are highly compatible with continuous-flow nitrate analyzers, are at best cumbersome on DA platforms.

“Using soluble nitrate reductase is an ideal approach to non-toxic nitrate testing with automated discrete analyzers,” he said.

Hach has tested NECi’s reductase on its Lachat Instruments AP300 Discrete Analyzer.

“We have an ongoing interest in finding an alternative method for nitrate analysis that eliminates cadmium from the process,” Butchko said. “We’re confident that our new Lachat AP300 will be among the first to commercialize a method for automated nitrate analysis using NECi technology.”

NECi is working with regulatory bodies to gain acceptance for its new method. In the meantime, the USGS findings provide solid science that customers can use now to eliminate cadmium, Campbell said.

“Not every application requires an EPA method,” he said, noting that a significant share of the company’s enzyme is now shipping to customers in Europe. Manual field test kits are also ideal for use by citizen groups whose volunteers monitor nitrate levels in streams and rivers not for EPA compliance, but as part of their ongoing environmental watchdog efforts.

For information on NECi nitrate reductase (NaR) products, visit www.nitrate.com.