Metal comparison based on field investigation reveals lithium phytoaccumulation patterns

Lithium is an emerging contaminant, yet little is known about how plants accumulate lithium and how this process differs from that of other metals. This study identified the lithium phytoaccumulation patterns based on field investigation and multi-metal comparison through 23 sets of soil and plant samples and 3 sets of soil-only samples collected from five sampling plots. Phytoindication revealed that lithium contents in Erigeron canadensis tissues from contaminated quadrats were several times higher than those from background quadrats, with the fold for lithium consistently exceeding that for copper, lead, and zinc. In contaminated quadrats C2 to C5, the mean lithium contents in the plant aerial parts and roots were 48.44 and 18.67 times higher than those detected in the remaining quadrats. Accumulation sensitivity indicated a much higher phytoaccumulation intensity for lithium compared to other metals. For each 1 mg/kg increase in mild acid-soluble lithium, the lithium content in plant aerial parts and roots increased by 33.11 mg/kg and 8.78 mg/kg on average. Spatial aggregation showed that lithium-contaminated quadrats were predominantly concentrated around a lithium salt factory. Soil-only samples collected from reclamation depot did not indicate potential lithium contamination. This study provides an empirical case and a technical approach for the monitoring and identification of lithium contamination associated with the global lithium cycle and the lithium battery industry chain. Future work should incorporate larger sample sizes, a wider variety of plant species, additional measurement variables, a greater spatial extent, and feasible tracing method.