Mapping of atmospheric heavy metal deposition in Guangzhou city, southern China using archived bryophytes

Abstract

Atmospheric heavy metal contamination is becoming a serious threat to environmental and human health in Chinese megacities. This study evaluated the concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) and Pb isotopic compositions in herbarium and native bryophytes collected from Guangzhou from 1932 to 2018. Relatively low mean metal concentrations were measured for bryophytes collected in the 1930s. The highest mean concentrations of Cd (0.72 ± 0.32 mg/kg), Cu (28.1 ± 9.8 mg/kg), Pb (125.9 ± 62.4 mg/kg) and Zn (273 ± 130 mg/kg) were found in the bryophytes from 1979 to 2000, following the commencement of the Reform and Opening-Up Program in 1978. The mean Pb concentrations (74.7 ± 6.3 mg/kg) decreased sharply from 2001 onwards, following the cessation of leaded petrol across the Chinese mainland in 2000. However, these values are still higher than those in 1950-1978, corresponding to a significant increase in atmospheric Pb emissions from coal combustion, nonferrous metal smelting and motor vehicle petrol consumption in China in the 2000s. The lead isotopic ratios of bryophyte archives (²⁰⁶Pb/²⁰⁷Pb 1.141-1.229, ²⁰⁸Pb/²⁰⁷Pb 2.376-2.482) indicate that lithogenic input and anthropogenic input arising from leaded petrol and industrial emissions have been the main sources of atmospheric heavy metal deposition in the city of Guangzhou over the past 85 years. Herbarium bryophyte can be utilised to reconstruct temporal and spatial shifts in atmospheric heavy metal deposition to better understand and manage the current air quality in Chinese megacities.

Keywords: Biomonitoring; Bryophytes; Industrial emission; Leaded petrol; Pb isotopic composition.