Toxicological effects of the aquatic herbicide, fluridone, on male water mites (Hydrachnidiae: Arrenurus: Megaluracarus)

Abstract

The acute toxicities for technical grade fluridone (Sonar™) and the commercial formulation of fluridone (Sonar®AS) were assessed for male water mites (Hydrachnidiae: Arrenurus: Megaluracarus). Signs of toxicity were evaluated by detection of locomotor dysfunction or death after exposure to concentrations of 100,000, 10,000, 1,000, and 100 μg/L of Sonar™ and 10,000, 5,000, 1,000, 100, and 10 μg/L of Sonar®AS in US EPA, moderately hard reconstituted water (MHRW). The median effective concentration (EC50) was 891 and 631 μg/L for Sonar™ at 48 and 96 h and less than 10 μg/L for Sonar®AS at 96 h. Increased duration of exposure to Sonar®AS from 48 to 96 h had a significant effect on increasing the rate of combined morbidity and mortality. At the lowest concentration of Sonar®AS tested, which is half the concentration allowed within 400 m of any functioning potable water intake for human usage, 40% of the mites were adversely affected at 48 h and 70% were affected after 96 h of exposure. This study demonstrates that Sonar®AS is 60-fold more toxic to water mites than the active ingredient alone. At currently acceptable application rates of 90-150 μg/L fluridone, the addition of ingredients classified as inert, as in Sonar®AS, result in an increased risk of adverse effects on populations of male water mites (Arrenurus: Megaluracarus) in aquatic ecosystems.

Sensitivity of freshwater molluscs to hydrilla-targeting herbicides: providing context for invasive aquatic weed control in diverse ecosystems

“…In a recent investigation of the toxicity of fluridone on male water mites (Arrenurus sp. ), Yi et al (2011) reported toxicities to technical grade fluridone similar to our Sonar À PR Ò commercial formulation results; however, they found water mites were 60 times more sensitive in tests with another commercial formulation (Sonar À AS Ò ; Table 2). In the context of typical treatment prescriptions for hydrilla, all of the mussel toxicity data generated in tests with Sonar Ò PR, including those generally reported for regulatory purposes (24 h for glochidia, 96 h for juveniles), are two or more orders of magnitude greater than the water column treatment maximum target concentration for Lake Waccamaw (5 mg/L), and are more than three times higher than the maximum label application rate of 150 mg/L (SePRO Corporation 2012).…”

“…The freshwater snail, S. viriginicus, was equally sensitive to the fluridone formulation Sonar À Genesis Ò as juvenile mussels were to the Sonar À PR Ò formulation (Table 1), and much more sensitive than other animals previously tested in commercial formulations of Sonar Ò (Hamelink et al 1986;Paul et al 1994), except for water mites (Yi et al 2011) (Table 2). The reported acute values for Sonar À Genesis Ò were 1.8 mg/L (96-h LC50) for walleye and 3.6 mg/L (48-h EC50) for Daphnia (SePRO Corporation 2011), which are values 3.6 to 7.2-fold higher than the snail 96-h LC50.…”

“…We selected herbicide treatment concentrations based on recommended application rates for treatment of hydrilla, maximum application rates reported on the product label, and acute toxicity data reported for other taxa in peer-reviewed literature (Crosby & Tucker 1966;Sanders 1969;Hamelink et al 1986;Paul et al 1994;Yi et al 2011) and on Material Data Safety Sheets (SePRO Corporation 2009, 2011UPI 2011UPI , 2012). An analytically verified 1304 mg/L (parts per billion) stock solution of Sonar À PR Ò (fluridone) formulation was prepared and provided by the SePRO Research and Technology Campus (Whitakers, North Carolina, USA).…”

“…Though toxicity data exist for some freshwater invertebrates and fishes (Crosby & Tucker 1966;Hamelink et al 1986;Paul et al 1994;Yi et al 2011), to our knowledge, no information has been published on the toxicity of fluridone or endothall to freshwater molluscs. Understanding the potential risks to this non-target faunal group is especially important because both freshwater mussels and snails are simultaneously highly imperilled and critically important to the functional ecology of freshwater systems (Lydeard et al 2004;Downing et al 2010;Allen et al 2012;Johnson et al 2013).…”

Unintended effects of the herbicides 2,4-D and dicamba on lady beetles

“…Nevertheless, ''inactive'' ingredients in pesticide formulations affect the toxicity of the active ingredient to a specific organism, and sometimes the adjuvants can be more toxic to non-target species than the active ingredients are (Cox and Surgan 2008;Mann and Bidwell 1999;Mullin et al 2015;Surgan et al 2010;Zhu et al 2014). For example, ''inactive'' ingredients found in common herbicide formulations used at label rates can be directly toxic to mites (Cowles et al 2000;Yi et al 2011), honey bees (Ciarlo et al 2011;Zhu et al 2014), aquatic insects (Dunkel and Richards 1998), and soil organisms (Pereira et al 2009). Indeed, the commercial formulation of 2,4-D can be ten times more toxic to late stage tadpoles of at least one frog species (Rhinella arenarum) than the active ingredient (Aronzon et al 2011), due in large part to the use of poly-ethoxylated tallowamine (POEA) as an adjuvant in aquatic herbicides (Howe et al 2004;Mann et al 2009).…”