Inter-compartmental transport of organophosphate and pyrethroid pesticides in South China: Implications for a regional risk assessment

• Transport fluxes of chlorpyrifos and pyrethroids were assessed in Guangzhou, China.
• Sediment acted as a sink for chlorpyrifos and pyrethroids.
• Air-to-water transport decreased the exposure risk of atmospheric chlorpyrifos.
• Dynamic transport might increase the risk of pyrethroids in air and sediment.
• Flux-based pesticide concentrations provide a way to estimate sediment toxicity.

The dynamic flux of an organophosphate and four pyrethroid pesticides was determined in an air-(soil)-water-sediment system based on monitoring data from Guangzhou, China. The total air–water flux, including air–water gaseous exchange and atmospheric deposition, showed deposition from air to water for chlorpyrifos, bifenthrin and cypermethrin, but volatilization for lambda-cyhalothrin and permethrin. The transport of the pesticides from overlying water to sediment suggested that sediment acted as a sink for the pesticides. Additionally, distinct annual atmospheric depositional fluxes between legacy and current-use pesticides suggested the role of consumer usage in their transport throughout the system. Finally, pesticide toxicity was estimated from annual air–water-sediment flux within an urban stream in Guangzhou. A dynamic flux-based risk assessment indicated that inter-compartmental transport of chlorpyrifos decreased its atmospheric exposure, but had little influence on its aquatic toxicity. Instead, water-to-sediment transport of pyrethroids increased their sediment toxicity, which was supported by previously reported toxicity data.

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