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Mighty Mites: Using Worms to Unearth Toxic Effects

Clare Coppa

The next time you’re digging the soil, remember the noble nematode. A handful of earth contains hundreds of the tiny worms that are aiding toxicology research. The millimetre-sized Caenorhabditis elegans has been studied internationally in the past 20 years because it shares many of the essential biological characteristics that are central problems of human biology, says University of Missouri professor Donald Riddle on his Web site. Calling someone a worm is a compliment according to this geneticist: “C. elegans has a nervous system with a ‘brain’ ... It exhibits behavior and is even capable of rudimentary learning ... Embryogenesis, morphogenesis, development, nerve function, behavior and aging and how they are determined by genes—the list includes most of the fundamental mysteries of modern biology ... All 959 somatic cells of its transparent body are visible with a microscope, and its average life span is a mere 2-3 weeks. Thus C. elegans provides the researcher with the ideal compromise between complexity and tractability.”

Using nematodes in place of earthworms and sometimes rats and mice, saves time, money, and space in the lab, says Professor Phillip Williams, Ph.D., an award-winning toxicologist and Georgia educator. “The C. elegans soil bioassays take only 24 hours and give similar results to earthworm tests that require 14 days,” he says. It is easily cultivated and uses less soil, which in many cases is hazardous and requires costly disposal.

In the 1980s, Williams began research on C. elegans at the Georgia Institute of Technology under Professor D. B. Dusenberry, who initiated nematode soil-toxicity tests with scientist S. G. Donkin. “Nematodes make up a tremendous percentage of the organisms found in the soil,” Williams says. “They play very important roles in the soil in terms of mineral cycling and nutrient cycling in normal biological processes.”

Williams decided to experiment with nematodes as a replacement for rodents in traditional toxicology testing. “It’s pretty exploratory at this point,” he says. “I think the area that has a lot of promise is screening chemicals for neuro-toxicity. C. elegans is the simplest organism with a centralized nervous system.” Nematodes have 302 neurons and humans, about 12 billion, Williams explains, but their nervous systems operate in the same way.

Under Williams’ advisement, University of Georgia graduate students employ C. elegans to investigate soil contamination or predict safe soil concentration levels for given contaminants. Their research has covered metal and chemical contamination of soil; industrial and municipal toxicants; and risk assessment of employee exposure to industrial pollutants.

Williams approached ASTM to standardize the soil toxicity tests he developed with UGA students. Based on their research, ASTM issued E 2172, Standard Guide for Conducting Laboratory Soil Toxicity Tests with the Nematode Caenorhabditis elegans, in December 2001. The standard test has advantages over tests with earthworms, Williams says: “The earthworm test takes between 100 and 400 grams of soil to run one test and ours takes 2.333 grams.” He used nematodes in 2000-01 to assess mine-related metal contamination in the Tizsa River, Hungary. The tiny worm enabled him to perform more tests with less soil and transport smaller hazardous-soil samples to the United States.

A member of ASTM Committee E47 on Biological Effects and Environmental Fate, Williams’ CV could wallpaper a suite in the Georgia Dome. He divides his time between research and teaching environmental, industrial, and public health at UGA, and at Emory University. His many accolades include an endowed professorship at UGA and a superior performance award from the U.S. Department of Labor. As well as co-authoring 51 technical articles and nine book chapters, he co-authored two textbooks: Industrial Toxicology: Safety and Health Applications in the Workplace (with J. Burson, 1985), and Principles of Toxicology: Environmental and Industrial Applications (with R. James and S. Roberts, 2000).

Look for further developments—Williams may solve a longstanding enigma with the wiley worm. He thinks the bacteria-feeding C. elegans may transmit pathogenic bacteria in the soil to crops and subsequently infect food with harmful bacteria like E. coli and Salmonella. //

Copyright 2002, ASTM

The centralized nervous system of the nematode C.elegans parallels the human nervous system.