Transfer of heavy metals from soil to tea and the potential human health risk in a regional high geochemical background area in southwest China

Abstract

Tea is one of the most consumed nonalcoholic beverages. The collaborative analysis of heavy metals soil-to-tea transfer and the associated potential risk to human health is important. This study features a survey of As, Cd, Pb and Cr in 144 paired soils and tea leaves from six main tea-growing regions (Fengqing, Linxiang, Yongde, Mangshi, Longling, and Yunlong) in Yunnan, China. The data showed soil acidification (pH = 4.77–5.17) in tea plantations, affecting heavy metals bioavailability thereby the transfer to tea leaves. Soil total and bioavailable As, Cd, Pb and Cr concentrations were 1.45–117, 0.025–0.67, 15.2–153, 3.8–409 mg kg−1 and 0.03–0.22, 0.011–0.38, 0.59–17, 0.013–0.47 mg kg−1, respectively. Specifically, As concentration in 20.8 % of the soil samples exceeded the standard value at 40 mg kg−1, while the standard-exceeding ratio of Cr was low at 9 %. Besides, Cd showed high bioavailability at 44–56.1 %, while Cr was low at 0.12–0.34 %. Arsenic, Cd, and Pb in tea leaves were within the standard values at 2, 1 and 5 mg kg−1. However, though soil Cr was low in standard-exceeding ratio and bioavailability, Cr accumulation in tea showed high standard-exceeding ratio (72.2 %). This indicated that soil heavy metals concentration and bioavailability are not necessarily to predict the pollution risk in tea leaves. Besides, tea favors to accumulate Cd, with 16 % showing BAF > 1. Though Cr in tea leaves was highly standard-exceeded and Cd was uptake-preferred, the target hazard quotients (THQ; <1) and aggregate risk hazard indexes (HI; 0.046) suggested that there was no potential risks to human health. This indicated that high pollution risk in tea leaves is not necessarily to induce risk to human health. The information helps to better understand the efficiency and influencing factors for heavy metals soil-to-tea leaves transfer and strategize how to more accurate evaluate the risks in soil pollution, food safety and human health.