Heavy metals and toxins can also be concentrated in the roots, or translocatedt o other plant parts. Many plant-based systems are most effective when the plants are actively growing. During dormant periods, treatment efficiencies generally decline and additional storage or other plans species may be needed. For example, water hyacinth could be utilized during warm weather, while other cold-tolerant plants such as duckweed or pennywort could be introduced during the winter months. In animal-based systems, the whole food web contributes to pollutant removal.
Larger animals provide a mechanism for complete removal of some pollutants.
Smaller animals such as invertebrates and free floating animals feed on algae and bacteria.