Investigation of the effects of gasoline-powered tea harvesters on tea plant

Tea is the most widely consumed non-alcoholic beverage among Turkish people. However, the application of chemical and organic fertilizers during tea cultivation, environmental pollution surrounding tea plantations, and the use of processing equipment lead to the accumulation of heavy metals in tea, posing potential health risks to consumers. This study is the first to investigate the effect of gasoline-powered tea leaf cutting machine on the heavy metal content of tea plants and the soils in which they are grown. In 2023, soil samples from selected tea gardens in the central district of Rize Province were collected before the first harvest period and after the third harvest period, while fresh tea leaf samples were collected during all three harvest periods. Processed tea samples were simultaneously obtained from the collected fresh tea leaves. Concentrations of lead (Pb), nickel (Ni), cobalt (Co), chromium (Cr), copper (Cu), zinc (Zn), and manganese (Mn) in soil, fresh tea, and processed tea samples were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results revealed that both fresh and processed teas had Mn and Cu concentrations, and processed teas had Cr concentrations exceeding the limits recommended by the World Health Organization. The soils from tea gardens were found to be contaminated with Co and Cu, with levels surpassing the threshold values established in the Regulation on the Control of Soil Pollution. Higher heavy metal concentrations were detected in both fresh and processed teas, as well as in their corresponding soils, when harvested using a gasoline-powered tea leaf cutting machine in clean areas and a tea shear in polluted areas. The lowest concentrations were found in areas harvested with tea shears in clean locations. Heavy metal levels in soils were highest before the first harvest period, while in fresh tea they were highest during the third harvest. In processed tea, Pb, Ni, Co, and Cu concentrations were highest in the third harvest, Cr in the second, and Zn and Mn in the first harvest. Based on average concentrations, heavy metals in soils were ranked as Mn ˃ Zn ˃ Cu ˃ Co ˃ Pb ˃ Cr ˃ Ni, in fresh tea as Mn ˃ Zn ˃ Cu ˃ Ni ˃ Co ˃ Cr ˃ Pb, and in processed tea as Mn ˃ Zn ˃ Cu ˃ Ni ˃ Cr ˃ Co ˃ Pb. These findings demonstrate that both harvest period and harvesting tools play a critical role in the accumulation of heavy metals in soil, fresh tea, and processed tea, providing a valuable foundation for ensuring product safety and quality management. It was predicted that the soil and tea (fresh leaf and manufactured tea) samples were affected by traffic and gases released from the gasoline-powered tea leaf cutting machine and were (and will remain) exposed to pollution directly or indirectly.