Heavy Metals in the Soil-Coffee System of Pu'er, China, a Major Coffee Producing Region in China: Distribution and Health Risks.

This study provides a comprehensive assessment of the distribution, bioaccumulation, and health risks associated with heavy metals in the soil-coffee system of Pu'er City, a major coffee-producing region in China. An analysis of the soil and corresponding plant samples (including fruit, stem, and leaf) from representative plantations revealed that, although the heavy metal concentrations in soils generally exceeded the local background levels, they remained below national risk screening thresholds. Hg was identified as the primary pollutant of concern, showing moderate to significant enrichment (EF: 2-20) and posing a moderate to considerable ecological risk (Ei: 40-160). In coffee plants, most heavy metals accumulated predominantly in the stems, whereas Pb and As were more concentrated in the leaves and fruits, respectively. Among the studied metals, only Cu exhibited a notable bioconversion tendency, with a biota soil accumulation factor (BSAF) close to 1, while other metals showed limited transfer (BSAF < 1). A generally negative correlation was observed between the soil metal content and BSAF, suggesting that elevated total concentrations do not necessarily enhance bioavailability. The health risk assessment indicated that coffee consumption poses no significant non-carcinogenic risk (HI < 1). However, the carcinogenic risks for Cr and As, albeit within acceptable limits (LCR between 10-6 and 10-4), still warrant attention. These findings underscore the importance of implementing targeted source control for Hg and Cr in soils and further investigating the transfer mechanisms of As to support the sustainable and safe production of coffee in this region.