Comparison of heavy metal accumulation ability in rainwater by 10 sponge city plant species

Rainwater heavy metal contamination is a growing problem worldwide, which damages the environment and human health. A primary challenge of sponge city designers is selecting suitable plants capable of surviving the toxic metals present in city rainwater. The concept of a sponge city to tackle urban surface-rainwater flooding and related urban rainwater management issues was established by People's Republic of China in 2014. Therefore, we studied the ability of sponge city plants to accumulate heavy metals from rainwater. Ophiopogon japonicus (Linn. f.) Ker-Gawl., Carex heterostachya Bge., Cornus officinalis Sieb. et Zucc., Sedum spectabile Boreau., Typha orientalis Presl., Lythrum salicaria L., Fatsia japonica (Thunb.) Decne. et Planch., Ilex chinensis Sims., Rosa chinensis Jacq., and Buxus bodinieri Levl. were selected as test plants, and their ability to accumulate four heavy metals (lead [Pb], cadmium [Cd], copper [Cu], and zinc [Zn]) was compared. Growth response and heavy metal accumulation across different species were compared over a 28-day enrichment cycle. The results showed that (1) Plant growth responses to heavy metals were significantly different. The most tolerant to heavy metals was Lythrum salicaria and the least tolerant was Rosa chinensis. (2) Concentrations of the heavy metals differed among sponge city plant species. In general, the concentration of Zn was highest, followed by Cu, Cd, and Pb. (3) The accumulation content of the same metal in different test species was related to the bioconcentration factor of the metal and the plant biomass. At the end of the enrichment cycle, Ophiopogon japonicus had the largest accumulation content for Pb, Cu, and Zn, and Lythrum salicaria had the highest accumulation content for Cd. (4) Considering the growth responses of plants and their final accumulation of heavy metals after the enrichment cycle, we concluded that Lythrum salicaria, Typha orientalis, and Ophiopogon japonicus are suitable for use in sponge cities to restore heavy metal-contaminated rainwater.