Sources and sinks of perchlorate in soil in coastal ice-free areas of Antarctica

Perchlorate (ClO₄⁻), a persistent inorganic compound, has harmful effects on human health. Natural ClO₄⁻ is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO₄⁻ in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO₄⁻ in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO₄⁻ concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO₄⁻ in soil. Concentrations of ClO₄⁻ in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO₄⁻ in soil. Thus, atmospherically formed ClO₄⁻ is the main source for soil in Antarctica. In general, ClO₄⁻ concentrations (0.1–5.1 μg kg⁻¹) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO₄⁻ in soil, and deeper depths for aqueous migration may contribute to the lower ClO₄⁻ concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO₃⁻, no correlation between NO₃⁻ and ClO₄⁻ in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO₄⁻ concentrations in soil, suggesting that biological reduction is not an important sink for ClO₄⁻ in Antarctic soil.