Springtime dynamics of semivolatile pesticides in air and water at Toolik Lake, Arctic Alaska

Pesticides that undergo atmospheric transport to Arctic areas and accumulate in winter snow and ice are known to undergo rapid release during spring melt. However, the timing and magnitude of melt-driven transport of pesticides into Arctic receiving waters, and the movement of these chemicals between environmental phases in Arctic lacustrine systems is not well understood. We measured legacy and current-use pesticides in the air, ice porewater, inlet stream, and lake water at Toolik Lake in Arctic Alaska during the spring in 2019 and 2022. Samples were collected with high temporal resolution (∼48 h) to capture the changes in pesticide concentrations associated with the springtime melt. Using this data set of pesticide concentrations from multiple environmental phases, we explored several ways that springtime environmental processes may have impacted pesticide fate in Toolik Lake. The positive relationship between pesticide concentrations in air and air temperatures indicates that localized pesticide volatilization from secondary sources was predominant, relative to long-range atmospheric transport, at Toolik Lake throughout the spring. The magnitude and trends of melt-driven pulses in stream water differed between isomers of hexachlorocyclohexane, suggesting that atmospheric deposition may have obscured the impact of melt dynamics for some pesticides. The timing of pesticide transfer from melting lake ice into underlying water was dependent on the chemical properties of each pesticide. Lastly, using a fugacity ratio approach, we show that concentrations of chlorpyrifos in lake water were highly dynamic due to rapid changes in air-water exchange.