Biodiminution of lithium in forest floor food webs

Lithium (Li) is an emerging contaminant of global concern due to its rapidly increasing demand for rechargeable batteries. However, concerns exist regarding its bioaccumulation and trophic transfer in natural food webs, with extremely scarce data particularly in terrestrial ecosystems. Here, we examined Li levels in soil, leaf litter and ground-dwelling invertebrates from 4 temperate forest sites across the United States (US) and 2 subtropical forest sites in Hong Kong (HK), China. Overall, we found statistical differences in Li levels between US and HK sites (p < 0.05) but not within regions (p > 0.05) while Li concentrations among invertebrates ranged from < 400 ng/g dry wt. (moths and butterflies) to ~ 9,000 ng/g dry wt. (earthworms). Indeed, biodimunition patterns (i.e., negative trophic magnification slope) were consistent among sites. Further, invertebrate classification by feeding habits revealed that the detritivorous invertebrates had the highest median Li (earthworms at 5,013 ng/g). Also, partially decomposed leaf litter retained ~ 5- to 10-fold higher Li compared to fresh litter (p < 0.05), implying that soil is the predominant source of Li to the food web components. Our study identifies that forest floor is a source of Li and suggests that the soils and decomposing litter can be an important source of Li to the lower forest floor food webs through differential feeding habits while Li does not exhibit any enrichment along the trophic transfer. We posit that detritivorous invertebrates are prone to chronic Li exposure, prompting them a priority for future Li ecological risk assessments in terrestrial ecosystems.