Source analysis of metals in the tea plant using linear correlation analysis combined with a lead-strontium isotope tracer

Many studies have focused on the concentrations of heavy metals (HMs) in Tieguanyin tea plants and surrounding soil; however, limited information is available on the specific sources of HMs in tea plantation trees. In this study, HMs in tea plants (roots, stems, old leaves, and young leaves) from Anxi County of the Fujian Province were determined by inductively coupled plasma mass spectrometry (ICP-MS). Additionally, correlation analysis, principal component analysis (PCA), and isotope tracers were used to analyze the sources of HMs pollution. The contribution rate of HMs in tea from different specific sources was further quantified by establishing a relative isotope mixing model. Our results showed that the highest Pb content in the roots was 23.89 μg·g−1 and was positively correlated with Sr and Ni in the roots, indicating that these three metals in the roots are from the same source, mainly from the soil. PCA analysis showed that Sr and Pb in factor 1 have higher positive charges in the young leaves, and their contribution rate was 27.16%. Sr is commonly used in the cement industry, indicating that factor 1 was mainly affected by industrial activities. The Pb and Sr isotope ratio showed that the average values of 208Pb/206Pb and 206Pb/207Pb in young leaves were 2.1124 and 1.1619, respectively, while the average values of 87Sr/86Sr in young leaves was 0.709774. The contribution rate of each potential source was quantitatively analyzed using the Pb-Sr multiple isotope mixture model, and agricultural activities were found to be the biggest contributors of HMs in tea. For example, agricultural sources of HMs found in old leaves and young leaves were 62% and 31%, respectively. Using multivariate statistical analysis methods combined with isotope tracing techniques, this study was able to identify sources of multiple heavy metals in Tieguanyin tea plants.