Research on Distribution Characteristics, Influencing Factors, and Maintenance Effects of Heavy Metal Accumulation in Bioretention Systems: Critical Review

Bioretention systems for collecting, filtering, and treating pollutants (e.g., heavy metals) in stormwater runoff have recently attracted increased attention from the scientific community. However, excess heavy metal accumulation after long-term operation may deteriorate effluent quality, affect plant growth and landscape benefits, and shorten the service life of bioretention systems. It has been shown that most of the heavy metals accumulated in bioretention systems were distributed in the soil/media layer, their concentration decreased with increasing soil/media layer depth, and heavy metals taken up by plants primarily accumulated in their roots. Accumulation of heavy metals in bioretention systems was closely associated with catchment characteristics, weather conditions, stormwater runoff quality, facility structure, vegetation species, and physicochemical properties of soil/media. Some practical maintenance measures were suggested to reduce heavy metal accumulation, including the use of pretreatment facilities, multimetal hyperaccumulators, regular topsoil replacement, innovative media materials, and soil amendments. Future research perspectives are also included to further advance research on the removal of heavy metals by bioretention systems.