Fish embryos a sentinel for toxins

Go Fishing for Environmental Contamination

Fish embryos a sentinel for toxins

RESEARCHERS HAVE HARNESSED the sensitivity of days-old fish embryos to create a tool capable of detecting a range of harmful chemicals. By measuring rates of oxygen use in developing fish, which are sensitive to contaminants and stressful conditions, the technology could reveal the presence of minute levels of toxic substances before they cause more obvious and substantial harm. It could be used as an early warning system against environmental contamination or even biological weapons, said Marshall Porterfield, PhD, an associate professor of agricultural and biological engineering at Purdue University (West Lafayette, Ind.)

Respiration, the process wherein animals and other organisms burn oxygen to produce energy, is often the first of a fish's bodily functions affected by contaminants. The technology uses fiber optics to quickly monitor this activity and produce results within minutes, Porterfield said in a statement released by Purdue.

"Say you are exposed to the common cold virus," he said. "Before symptoms develop and you become aware of the bug's presence, it has already begun to attack your cells. Similarly, fish, and other organisms are affected by contaminants before behavioral changes appear. Our technology detects heretofore undetectable changes to act as an early warning system."

In a study published online in August in Environmental Science and Technology, the system detected the presence of several common pollutants such as the widely-used herbicide atrazine-even at levels near or below those that the U.S. Environmental Protection Agency deems acceptable for drinking water.

"This means the technology could not only help monitor environmental quality, but may be used to enforce important water quality standards," said Marisol Sepul-veda, PhD, lead author and assistant professor of forestry and natural resources at Purdue. Testing also registered noticeable changes in the respiratory activity of fish embryos when the heavy metal cadmium was present at levels 60 times lower than the EPA limit, she said.

Throughout the study, contaminants did not destroy the eggs of laboratory-raised fathead minnows, a commonly studied fish species. This further demonstrates the tool's ability to discern subtle changes before they become fatal, Sepulveda said.

In the laboratory, researchers first manually positioned a tiny optical electrode, or optrode, just outside individual embryos of two-day-old fathead minnows. At 1.5 mm in diameter, they were slightly smaller than the head of a pin, said primary author and Purdue doctoral student Brian Sanchez.

Purdue University researchers use an optical electrode to measure oxygen consumption in a two-day-old fathead minnow embryo.

SOURCE: MARSHALL PORTERFIELD, PHD

A fluorescent substance coated the electrode tip, its optical properties varying predictably with oxygen concentration. This allowed researchers to take quick measurements at locations only micrometers apart, moving the electrode via a computer-driven motor, Sanchez said. These readings then allowed researchers to calculate respiration rates within the eggs, he said.

Using a self-referencing technique Porterfield developed over the last decade, he and the team measured each egg with and without contaminants present. This allowed each embryo to serve as its own control, he said, providing more reliable results. Porter-field said the technology could be used on other organisms.

A prototype could be ready to test in the field in four years if improvements continue, said Porterfield. The technology currently tests immobilized eggs in a laboratory setting but there are plans to make the tool more versatile. During the study the technology detected four of five common pollutants tested, all known to act upon organisms in different ways: atrazine, cadmium, pentachlorophenol (an antifungal), and cyanide.