Atmospheric deposition and air‐sea gas exchange fluxes of DDT and HCH in the Yangtze River Estuary, East China Sea

Abstract

The Yangtze River Estuary (YRE) is strongly influenced by the Yangtze River and lies on the pathway of the East Asian Monsoon. This study examined atmospheric deposition and air‐sea gas exchange fluxes of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) to determine whether the YRE is a sink or source of selected pesticides at the air‐water interface under the influences of river input and atmospheric transport. The air‐sea gas exchange of DDT was characterized by net volatilization with a marked difference in its fluxes between summer (140 ng/m2/d) and the other three seasons (12 ng/m2/d), possibly due to the high surface seawater temperatures and larger riverine input in summer. However, there was no obvious seasonal variation in the atmospheric HCH deposition, and the air‐sea gas exchange reached equilibrium because of low HCH levels in the air and seawater after the long‐term banning of HCH and the degradation. The gas exchange flux of HCH was comparable to the dry and wet deposition fluxes at the air‐water interface. This suggests that the influences from the Yangtze River input and East Asian continental outflow on the fate of HCH in the YRE were limited. The gas exchange flux of DDT was about fivefold higher than the total dry and wet deposition fluxes. DDT residues in agricultural soil transported by enhanced riverine runoff were responsible for sustaining such a high net volatilization in summer. Moreover, our results indicated that there were fresh sources of DDT from the local environment to sustain net volatilization throughout the year.

Impacts of Seasonal Variation on Organochlorine Pesticides in the East China Sea and Northern South China Sea

“…Despite being prohibited for more than three decades in China, OCPs are still found ubiquitously in the environment including air, water, soil, sediments, and organisms . These anthropogenic OCPs can be transferred from land-based sources to the marine environment via surface runoff, atmospheric transport and deposition, and other direct or indirect discharge processes and eventually dispersed in the ocean. , …”

Levels, Sources and Potential Risks of Polychlorinated Biphenyls and Organochlorine Pesticides in Sediments of Qingduizi Bay, China: Does Developing Mariculture Matter?

“…More than 10,000 tons of PCBs, 0.4 million tons of DDTs, and 4.5 million tons of HCHs were used in China from the 1950s to 1980s owing to the population explosion and the increasing requirements for food (Wei et al, 2007;Bao et al, 2012). Though, in China, the manufacture and agricultural usage of most PCBs and OCPs were banned in 1974 and 1983, respectively (Wang et al, 2005), these organic chemicals can still be routinely detected in various environmental compartments (i.e., in air, water, soil, sediments, and organisms) (Adeleye et al, 2016;Li et al, 2017;Zhao et al, 2018). Due to the slow degradation of PCBs and OCPs, the residues and their catabolites would persist in the ecosystem for a long time (Yu et al, 2014;Wu et al, 2015).…”

Seasonal Variation of Legacy Organochlorine Pesticides (OCPs) From East Asia to the Arctic Ocean

“…Kriging interpolation was applied to the analysis of ocean current movements (Zheng et al, 2017) (Text S3). States of OCP phase equilibrium at the air‐water interface were estimated using the fugacity computing method based on Whitman two‐film theory (Li et al, 2017; Odabasi et al, 2008). Detailed descriptions of the air‐sea exchange flux calculations are provided in the SI (Text S4).…”

“…These compounds, which include hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), have proved to be persistent and bioaccumulative in the environment, have the potential for long‐range atmospheric transport, and have proved to be toxic to wildlife and humans (Li et al, 1998; Stemmler & Lammel, 2009; Willett et al, 1998). Because of their ecological and health risks, these pesticides started to be phased out globally apart from specific uses such as DDT for malaria vector control, and they have been added to the Persistent Organic Pollutants (POPs) list of the Stockholm Convention (Cai et al, 2010; Li et al, 2017; Ma et al, 2018). Legacy OCPs have been detected globally in atmospheric, aquatic, and geological systems and in remote regions such as the Himalayas and polar regions (Bailey et al, 2000; Cai et al, 2012; Gao et al, 2010; Huang et al, 2013; Li, 1999; Ren et al, 2019).…”