The water hyacinth (Eichhornia crassipes) may be used as a sensitive biological indicator for continuously monitoring trace quantities of toxic heavy metals in aquatic systems. A river water system polluted with cadmium was simulated while other factors of temperature, day-night cycle, water quality, and light intensity remained constant. When the water hyacinth is maintained in river water containing 0.001 mg/l. of cadmium chloride, the plant's root system will concentrate this element at an average rate of 0.9, 1.4, and 3.0 μg Cd/g root dry weight after 24, 48, and 72 hr exposure periods, respectively. At a higher cadmium concentration of 0.01 mg/l., cadmium was concentrated in the roots much faster to levels of 6.8, 13.6, and 39.1 μg/g root after 4, 8, and 24 hr exposure periods, respectively. At initial concentrations of 0.05 mg/l. cadmium, the roots contained 29.5, 48.8, and 156 μg/g root following 4, 8, and 24 hr exposure periods, respectively. During these same time intervals, the water hyacinth sorbed 56.7, 153, and 281 μg/g root when the initial cadmium concentration was increased to 0.10 mg/l. The water hyacinth tops can also assist in the monitoring process when cadmium contamination levels are 0.10 mg/l. and greater. At this initial cadmium concentration, cadmium is translocated into the tops. After 8 hr, the tops averaged 1.1 μg/g top. After 24 hr, this concentration was increased to 6.1 μg/g top
