Persistence of aerially applied mosquito-pesticide, Naled, in fresh and marine waters

Field Assessment of Naled and Its Primary Degradation Product (Dichlorvos) in Aquatic Ecosystems Following Aerial Ultra-low Volume Application for Mosquito Control

“…Organophosphate insecticides are often chosen for vector control because of their acute toxicity and short half-lives in the environment (Desouky et al 2013 ). During the Zika virus outbreak in the United States in 2016, vector control agencies began to apply naled (an organophosphate insecticide) more frequently, and over areas that were not previously sprayed with pesticides (Jones et al 2020 ; McAllister et al 2020 ). The increased use of naled highlighted the need for more information regarding the fate and transport of this insecticide in various environmental conditions and aquatic ecosystems.…”

“…However, naled is applied directly over aquatic ecosystems, and spray drift can introduce the pesticide to non-target ecosystems. Past studies have shown that measurable concentrations of naled are detected in the air (Schleier and Peterson 2010b ; Zhong et al 2010 ), water (Jones et al 2010 ; Phillips et al 2014 ), and on surfaces (Pierce 2008 ) following ULV applications for adult mosquito control. After an aerial application, naled was detected on residue samplers 19 km from the target spray area (Zhong et al 2010 ).…”

“…Therefore, ultraviolet radiation and humidity affect the degradation of naled in air and on terrestrial surfaces, and the half-life on surfaces can range from 1.4 to 8 h (Tietze et al 1996 ). The degradation of naled in freshwater is affected by light, organic carbon, and temperature, and the half-life at 23 °C is approximately 15 min when exposed to light and 20 h in the dark (Jones et al 2020 ). Naled is used to directly kill nuisance organisms, but the organophosphate insecticide is non-specific and can affect non-target species (Schleier and Peterson 2010a ).…”

“…While naled degrades quickly in most field conditions, the breakdown product dichlorvos (2,2-dichlorovinyl dimethyl phosphate) is also an organophosphate insecticide and a possible human carcinogen (Cox 2002 ). In dark conditions at 23 °C, the half-life of dichlorvos is about 7 days, but light conditions can result in rapid degradation (half-life < 67 min; Jones et al 2020 ). Following naled applications, the toxicity of water samples to the non-target freshwater invertebrate Ceriodaphnia dubia was mainly attributed to dichlorvos concentrations in the water (Phillips et al 2014 ).…”

“…The fate and transport of naled and dichlorvos following a ULV application are dependent on the weather (Schleier and Peterson 2010b ), time of ULV application (Mount et al 1996 ), and site-specific characteristics such as water movement (Phillips et al 2014 ; Pierce et al 2005 ). Since naled is applied during evening hours (when photolysis is minimal) in the central valley of California, both the parent compound and degradation products may persist and could potentially be transported away from the application area (Jones et al 2020 ; Pierce et al 2005 ; Tietze et al 1996 ). In flowing waters, exposure to aquatic organisms may be ephemeral (Stavola 2004 ), and mixing may slightly increase hydrolysis rates (Noblet et al 1996 ).…”