The researchers studied how alfalfa plants can help clean up soil contaminated with a harmful chemical called PCB 77. They used a special setup to see how well the plants removed the chemical from different areas around their roots. They found that the soil near the roots had the highest PCB removal rate, followed by the area slightly farther away, and then the farthest area. The number of helpful bacteria in the soil increased near the roots, and the diversity of these bacteria improved. Overall, the alfalfa plants were very effective at cleaning up the contaminated soil, improving the soil's health and diversity of bacteria.