Co-contamination of Cu and Cd in paddy fields: Using periphyton to entrap heavy metals

•Periphyton was capable of simultaneously entrapping Cu and Cd from paddy fields.•Cu and Cd bioavailability decreased with time after exposure to periphyton.•Periodic adsorption–desorption was the main mechanism used to remove Cd and Cu.•Periphyton was able to adapt to steady accumulation of Cu and Cd.•The inclusion of periphyton will help entrap heavy metals in paddy fields. The ubiquitous native periphyton was used to entrap Cu and Cd from paddy fields. Results showed that Cu- and Cd-hydrate species such as CuOH+, Cu2(OH)22+, CdOH+, and Cu3(OH)42+ decreased with time in the presence of periphyton. When the initial concentrations of Cu and Cd were 10mg/L, the heavy metal content in the periphyton fluctuated from 145.20mg/kg to 342.42mg/kg for Cu and from 101.75mg/kg to 236.29mg/kg for Cd after 2h exposure. The concentration of Cd in periphytic cells varied from 42.93mg/kg to 174mg/kg after 2h. The dominant periphyton microorganism species shifted from photoautotrophs to heterotrophs during the exposure of periphyton to Cu and Cd co-contamination. Although Cu and Cd could inhibit periphyton photosynthesis and carbon utilization, the periphyton was able to adapt to the test conditions. Cu and Cd accumulation in rice markedly decreased in the presence of periphyton while the number of rice seeds germinating was higher in the periphyton treatments. These results suggest that the inclusion of native periphyton in paddy fields provides a promising buffer to minimize the effects of Cu and Cd pollution on rice growth and food safety.