The incomplete burning of fossil fuels, such as gas and coal, leads to the creation of toxic, oily substances that are hard to break down and accumulate in the environment. These pollutants are known as polycyclic aromatic hydrocarbons (PAH) some of which are carcinogenic or mutagenic. Ridding soils of these pollutants can be difficult and expensive. But certain plants, such as ryegrass, passively sip PAHs out of the soil and store them in areas of the plant where oily substances can dissolve, such as cell walls and vacuoles. The same low-energy processes that pull water through the roots also help to pull PAHs into plant tissues.
"Uptake from water and soil via plant roots is a major pathway of PAH entry into plants...PAHs first adsorbed to root surfaces and then passed through the membranes of adjoining cells before accumulating in cell walls and vacuoles. The amount of uptake depended primarily on the lipid content of plant roots, in which protein, fats, nucleic acids, cellulose tissues, and other components all contain lipophilic components, which appear to be the primary domains where PAHs accumulate once they penetrate plant root cells." (Kang et al. 2010:2)
"The lipid contents of intracellular components determine the extent of lipophilic compound accumulation, and the diffusion rate is related to the concentration gradient established between cell walls and organelles inside cells." (Kang et al. 2010:5)