Sublethal effects on Simocephalus vetulus (Cladocera: Daphnidae) of pulse exposures of cypermethrin

https://doi.org/10.1016/j.ecoenv.2020.110546Get rights and content

Highlights

  • A single brief exposure of cypermethrin to Simocephalus vetulus inhibits feeding.

  • Repeated pulse exposures of cypermethrin reduce fecundity and population growth.

  • Simocephalus vetulus is affected by cypermethrin toxicity in the environment.

  • Sensitive species would be affected, changing invertebrate assemblage structure.

Abstract

Pyrethroids are among the most widely applied insecticides worldwide and cypermethrin is the pyrethroid most used in Argentina. Pesticides used in crops can reach adjacent watercourses through runoff and may lead to non-target fauna receiving toxic pulse exposures. The aim of this study was to determine the effects of cypermethrin pulse exposures on the widely distributed crustacean Simocephalus vetulus. The 48h-LC50 of cypermethrin for S. vetulus was determined at 0.18 ± 0.09 μg/L. To assess the effects of cypermethrin under environmentally realistic exposures, two experiments were performed. In the first one, specimens were exposed for 90 min to cypermethrin at 0.02 (T1), 0.2 (T2) and 1 μg/L (T3), transferred to clean water and monitored for 24 h as regards survival and feeding rates; specimens exposed to T2 and T3 concentrations showed significant lower feeding rates than those in the control group. In the second experiment, specimens were exposed for 90 min every 7 days and monitored over 25 days; S. vetulus showed lower cumulative fecundity and reproduction rates at all concentrations tested, and lower population growth at the highest concentration. All exposure concentrations lay within reported environmental concentrations and risk assessment indicated risk (RQ > 1), suggesting that sensitive species would be affected by such pulse exposures of cypermethrin. The present study thus suggests that ongoing agricultural practices affect the non-target invertebrates in streams adjacent to crops.

Introduction

South America is the main soybean farming region in the world, Brazil and Argentina together being responsible for the 49% of global production (Oliveira and Hecht, 2016). The implementation of an intensive system based on monoculture, genetically modified seeds, no-till farming and intense agrochemicals usage led to a rise in crop production from 32 to 100 million tons between the 1970s and 2018 (MA, 2019). Correspondingly, insecticide consumption rose from 39,000 tons in 1991 (Moltoni, 2012) to 336,000 tn in 2011 (CASAFE, 2013).

Pyrethroids have gradually replaced the highly persistent organochlorine and organophosphate pesticides for growing and stored crops, in veterinary medicine, and in vector control, becoming one of the most used types of insecticides worldwide (Xiao et al., 2012). In Argentina, cypermethrin is the most widely used pyrethroid (CASAFE, 2013). Being highly hydrophobic (Kow = 6.3) it is largely adsorbed to sediments (Maund et al., 2002; Yang et al., 2006), resulting in its fast disappearance from the water (Knauer et al., 2017; Mugni et al., 2011). Despite its low persistence in the environment (Schäfer et al., 2011), there is rising concern about contamination by pyrethroids in freshwater systems, particularly its toxicity to non-target fauna (Loetti and Bellocq, 2017; Macagnan et al., 2017; Subrero et al., 2019) and its bioaccumulation risks (Arisekar et al., 2019; Corcellas et al., 2015; Riaz et al., 2018).

Insecticides reach watercourses by surface runoff produced by rains following applications in adjacent plots (Jergentz et al., 2005; Mugni et al., 2011; Schulz, 2004). A wide range of cypermethrin concentrations in the regional aquatic systems have been reported, ranging from 0.05 μg/L (Jergentz et al., 2005) to 6.6 μg/L (Etchegoyen et al., 2013) in water, and from 0.57 to 221 μg/kg in sediments (Etchegoyen et al., 2013). Insecticide non-point sources reaching streams might represent a risk to non-target fauna.

The toxic effects of pyrethroids have mainly been studied as regards continuous exposures (Day and Kaushik, 1987; Kim et al., 2008; Martínez-Jerónimo et al., 2013; Toumi et al., 2013). However, it has been proposed that pesticides enter into streams in pulses (Richards and Baker, 1993; Liess et al., 1999) resulting in ephemeral peak exposure concentrations reaching non-target species. Thus, setting up pulse exposures followed by non-exposure periods along the species’ life cycles could be an environmentally realistic experimental design.

Daphnids (Cladocera: Daphniidae) are common organisms used in toxicity tests to assess the effects of pesticides on non-target aquatic fauna. Among them, Daphnia magna Straus 1820 is the most extensively used species in international water quality protocols (OECD, 2000; ISO, 2012; USEPA, 2016). Nevertheless, it does not occur naturally in South America (Hebert, 1978). On the other hand, the cladoceran Simocephalus vetulus (Müller 1776) is commonly present in Argentina (Paggi, 1995); it has been used as a model organism in toxicity tests (Chen et al., 2004; Olvera-Hernández et al., 2004; Schroer et al., 2004; Willis et al., 1995; Wu et al., 2007). Juárez and Villagra de Gamundi (2007) and Reno et al. (2014) used S. vetulus as model organism in Argentina to assess the toxicity of lindane and glyphosate, respectively. However, experiments assessing the sublethal effects of pyrethroids on S. vetulus after brief exposures to reported field concentrations haven't previously been reported in the country.

The aim of the present study was to determine the effects of pulse exposures of cypermethrin on S. vetulus in order to improve the assessment of the impact of insecticides on non-target freshwater fauna under realistic environmental scenarios.

Section snippets

Test chemical

Cypermethrin (C22H19Cl2NO3) or (RS)-alpha-cyano-3-phenoxybenzyl-(1RS,3RS,1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate (IUPAC) is the active substance in the Galgotrin® (25%) formulation marketed by Chemotécnica S. A. (https://www.chemotecnica.com/). Stock solutions were prepared by dissolving the insecticide in 100 ml analytical grade acetone (Baker) to achieve a 1000 μg/L concentration stock solution.

Test organism

Simocephalus vetulus was obtained from the Sin Nombre stream

Acute toxicity and sensitivity comparison

Mean registered mortalities of S. vetulus after 48 h cypermethrin exposure are shown in Fig. 1. The mean determined 48h-LC50 of cypermethrin for S. vetulus in three independent assays was 0.18 ± 0.09 μg/L. Lethal concentrations of several insecticides for S. vetulus have been reported, such as chlorpyrifos (van Wijngaarden et al., 1993), carbaryl, methomyl (Mano et al., 2010), malathion (Olvera-Hernández et al., 2004) and lambdacyhalothrin (Schroer et al., 2004). To our knowledge, the lethal

Conclusions

The reported 48 h-LC50 of cypermethrin for S. vetulus indicated that the latter is a sensitive species and could be a reliable indicator of cypermethrin toxicity in the environment. Experiments showed that a single 90 min-pulse exposure at environmentally relevant concentrations inhibits feeding, and repeated pulse exposures reduce fecundity and population growth. Present results suggest that a non-target population exposed to pulses of cypermethrin will decrease its feeding rate, fecundity and

CRediT authorship contribution statement

Marina Arias: Methodology, Formal analysis, Investigation, Writing - original draft. Carlos Bonetto: Conceptualization, Writing - review & editing, Supervision, Funding acquisition. Hernán Mugni: Conceptualization, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors acknowledge reviewers and editors for valuable comments and suggestions. We thank to Noelia S. Ferrando for her assistance in data analysis. This research was supported by the National Scientific and Technical Research Council (CONICET) (PIP 2011 No. 0180) and the Argentine National Agency for the Promotion of Science and Technology (ANPCyT) (PICT 2010-0446).

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