The researchers studied how adding biochar to different types of soil affects the behavior of a common soil contaminant called phenanthrene. They found that biochar can help trap phenanthrene in the soil, preventing it from leaching into water sources. However, biochar also reduced the breakdown of phenanthrene in the soil, making it less available for plants and microbes. Overall, adding biochar to soils with low organic matter can increase the ability of the soil to trap phenanthrene, but its effects may be limited in soils with already high organic matter content.