Nickel in Soil and Safety of Tea-drinking

Extensive sampling on the soils and the tea plants grown on them were conducted at 8 plantations in central Fujian for analyses to assess the nickel (Ni) contamination in soil and the Ni transportation, accumulation and distribution from the soil to various parts of a tea plant, as well as how they were affected by the soil physiochemical properties. Safety of the tea brewed from the tea samples was gauged by the target hazard quotient (THQ), and the maximum Ni in tea leaves and soil determined accordingly. The average total and available Ni in the soils were found to be 18.58 and 0.90 mg·kg^-1, respectively. They were both below the safety thresholds specified by GB 15618-2018. Other than branches, the sampled plant tissues showed a significant correlation on the total and available Ni with the soil. Ni in the lateral and main roots significantly correlated with the total Ni, available Ni, pH and organic matters in soil but inversely to the available phosphorus in soil. The amounts and enrichment coefficients of Ni in different plant parts differed. They ranked in the order of lateral roots>main root or main stem>old leaves>branches or young shoots. The significantly higher Ni enrichment coefficients of the roots and the stems indicated that these parts accumulated more of the Ni transported to a plant than did the leaves. The rate of Ni leaching from tea leaves to steep water was 41.75%. As a result, on average the Ni content in brewed tea was merely 116.41 μg·L^-1, which was significantly lower than the limit for drinking water (GB5749-2006). With the THQ of the brewed tea being less than 1, it was concluded that normal tea-drinking was deemed safe, unless the Ni concentration is greater than 191.35 mg·kg^-1 or a daily usage beyond 542.86 g.