Lead in soils and plants: A literature review

The distribution of lead in the environment is altered by the activities of man, principally through its use as a fuel additive. Lead appears in automobile exhaust as halides, hydroxides, and oxides, with lesser amounts of carbonates and sulfates. Lead concentrations decrease rapidly with depth in the soil and distance downwind from a source, and show a positive correlation with traffic volume. Lead in soil is moved slowly by leaching, due to sorption and formation of insoluble compounds. Sorption of lead by soils is positively correlated with cation exchange capacity. Lead can be taken up by plant roots if in an available form, but soil sorption phenomena and precipitation prevent uptake of large amounts unless soil lead levels are extremely high. Lead can be absorbed by plant foliage but much of it is apparently in the form of a surface deposit. Lead content of plants grown in natural soils is generally less than 10 ppm d.w. When taken up by a plant, lead may be found principally in the roots, with little translocation to the shoot. Lead uptake is enhanced by low soil pH and can be reduced by liming the soil.