How lead can easily enter the food chain--a study of plant roots

Using the root test, the relationship between the amount of lead in plant tissues and the level of the root growth inhibition was examined for twelve food plant species. 345 mg to 8152 mg Pb.kg-1 dry wt. inhibited root growth only by 5 to 36% as compared to the control. At least 96.6% of lead was bound in cells of root tips. Most of the lead was accumulated in cell walls, vacuoles and sometimes in dictyosomal vesicles. Lead accumulating in these cell compartments is separated from cell cytoplasm and therefore is no longer toxic for root cells. The results show that amounts of lead much bigger than those observed in the environment can now easily enter the food chain via plants. High tolerance to lead in plant roots is quite unfavourable for other members in the food chain, including man.