Elsevier

Aquatic Toxicology

Volume 185, April 2017, Pages 58-66
Aquatic Toxicology

Toxicity of abamectin and difenoconazole mixtures to a Neotropical cladoceran after simulated run-off and spray drift exposure

https://doi.org/10.1016/j.aquatox.2017.02.001Get rights and content

Highlights

  • Toxicity of abamectin and difenoconazole was determined to a tropical cladoceran.

  • Mixture toxicity of the two pesticides was also evaluated.

  • Risks of realistic runoff and spray drift exposure were assessed.

  • Synergistic interactions occurred in mixtures of both commercial products.

  • Realistic exposure to pesticide mixture is likely to impose risks to aquatic biota.

Abstract

Aquatic risk assessments of pesticides in tropical countries have often been disputed for being largely based on risk evaluations conducted in temperate regions. Although pesticide sensitivity comparisons between temperate and tropical freshwater organisms have indeed not revealed consistent differences, risk assessments are currently still based on a relatively small tropical toxicity dataset. In addition, greater levels of runoff and spray drift may be expected in tropical than in temperate agroecosystems, indicating that aquatic life in edge-of-field water bodies is likely to be subjected to higher concentrations of pesticides and their mixtures. The aim of the present study was to evaluate the toxicity of Kraft® 36 EC (a.i. abamectin), Score® 250 EC (a.i. difenoconazole) and their mixture to the Neotropical cladoceran Macrothrix flabelligera. Laboratory toxicity tests with the individual formulated products indicated EC50–48 h values of 3.1 and 659 μg a.i./L given as nominal test concentrations, respectively. Mixtures of the two pesticides revealed a concentration-dependent deviation of the independent action model, with antagonism at low and synergism at high pesticide mixture concentrations. Laboratory toxicity tests were also conducted with microcosm water that was treated with the individual or mixtures through runoff or direct overspray. Microcosm tanks receiving runoff water from experimental soil plots applied with recommended doses of the individual pesticides did not show toxicity to the test organism. Microcosms that received runoff water containing the pesticide mixture, however, did cause a short-term effect on immobility. The microcosms that were treated by direct overspray of both pesticide formulations showed the most pronounced toxic effects. Study findings suggest a potential risk of these pesticides at environmentally relevant concentrations, especially when they are both present.

Introduction

Pesticides applied to agricultural fields to increase the yield may contaminate adjacent watercourses via spray drift, run-off, drainage and/or accidental spills (Capri and Trevisan, 1998). Developed countries, situated in temperate regions, are shifting towards reduced pesticide use as a result of improvements in agronomic practices, whereas developing countries, most of which are in tropical regions, are increasing their use of pesticides and fertilizers as they become wealthier (Sanchez-Bayo and Hyne, 2011, Lewis et al., 2016). Brazil, for example, became the world's top pesticide market consumer in 2008, accounting for approximately 20% of the total world use (Albuquerque et al., 2016). Despite this high use of pesticides in tropical countries like Brazil, there is still relatively little knowledge about the fate and toxicity of pesticides in tropical aquatic ecosystems as compared to temperate systems (Daam and Van den Brink, 2010, Sanchez-Bayo and Hyne, 2011, Carriquiriborde et al., 2014, Diepens et al., 2014, Lewis et al., 2016).

In the absence of data derived under (local) tropical conditions, risk assessments in tropical countries often rely on temperate toxicity data, although it may be debatable whether the fate and effects of chemicals are comparable in geographically distinct ecosystems (Daam and Van den Brink, 2010). Sensitivity comparisons of tropical and temperate species to pesticides have not demonstrated a consistent greater or lesser sensitivity of tropical species as compared to their temperate counterparts, although such comparisons are based on a relatively small tropical dataset (e.g. Maltby et al., 2005, Kwok et al., 2007, Rico et al., 2011). On the other hand, edge-of-field waterbodies in tropical agroecosystems have often been reported to be especially prone to pesticide contamination through runoff resulting from intensive irrigation practices and tropical rainfall (Daam and Van den Brink, 2010, Lewis et al., 2016, Novelli et al., 2016). Furthermore, pesticides are often applied in close proximity to water bodies surrounding agricultural fields, resulting in relatively high levels of spray drift (Castillo et al., 1997, Daam and Van den Brink, 2010, Sanchez-Bayo and Hyne, 2011). Other frequently noted relatively important entry routes of pesticides in tropical countries are dangerous transportation and storage conditions, unnecessary applications and overuse, use of cheaper but more hazardous pesticides, and washing of application equipment in water bodies (Daam and Van den Brink, 2010 and references therein). Consequently, despite the absence of a clear difference in sensitivity, tropical freshwater organisms are likely to be subjected to higher (peak) pesticide concentrations and hence risks in real-world field conditions than their temperate counterparts.

The main Brazilian strawberry crop area in the municipality of Bom Repouso (Minas Gerais) has a tropical climate by altitude, and can be classified as a monsoon-influenced humid subtropical climate according to Köppeńs classification. It is an agricultural area with intensive use of pesticides and previous field studies in this area identified the insecticide/acaricide Kraft® 36 EC (a.i. abamectin) and the fungicide Score® 250 EC (a.i. difenoconazole) as the main pesticides intensively used throughout the year (Nunes, 2010, Nunes and Espindola, 2012). These pesticides are hence likely to occur simultaneously in edge-of-field water bodies in this region and this pesticide mixture may have greater toxic effects to aquatic life in these ecosystems than the individual compounds.

The aim of the present study was to evaluate the toxicity of Kraft® 36 EC and Score® 250 EC to the Neotropical cladoceran Macrothrix flabelligera, a species native and of common occurrence in Brazilian freshwaters (Güntzel et al., 2003, Moreira et al., 2014). Laboratory toxicity tests were conducted with the individual compounds to establish their respective toxicity thresholds. Mixtures of both compounds were also tested to evaluate their combined effect and its underlying mechanism. The potential risks related with exposure to both compounds, alone and in combination, likely to occur in the field through runoff and spray drift was also evaluated through semi-field testing.

Section snippets

Test organism and culture conditions

Macrothrix flabelligera Smirnov, 1992 (Crustacea, Cladocera, Daphnidae) was initially isolated from the Lobo-Broa Reservoir (Itirapina, SP, Brazil) and had been kept in stock cultures for more than 4 years at the Ecotoxicology Laboratory of the Federal University of São Carlos (Brazil). The culture is maintained under controlled temperature (25 ± 1 °C) and photoperiod (12 h light:12 h dark; light intensity ± 1000 lx) in reconstituted water prepared according to standard ABNT (2005) with pH 7.0–7.8,

EC50 values for abamectin and difenoconazole

The mean EC50-48 h for M. flabelligera obtained from the twenty reference tests with potassium dichromate (K2Cr2O7) was 54 ± 17 μg/L (mean ± SD) with a 95% confidence interval (CI) of 46–61 μg/L. All toxicity tests data met all the validity criteria laid down in the guidelines of the Brazilian Association of Technical Standards (ABNT, 2005). Physicochemical conditions of the test solutions used were (minimum – maximum value): pH 7.0–7.7, water temperature 24.5–25.6 °C, electrical conductivity 152–159 

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgements

We thank the National Council for Scientific and Technological Development (CNPq). This work was supported by the Brazilian government through the Special Visiting Researcher program (MEC/MCTI/CAPES/CNPq/FAPs reference 402392/2013-2) and the Portuguese government (FCT) through a postdoc grant for the second author (SFRH/BPD/109199/2015).

References (67)

  • A.F. Albuquerque et al.

    Pesticides in Brazilian freshwaters: a critical review

    Environ. Sci.: Processes Impacts

    (2016)
  • A. Ali et al.

    Ecotoxicological effects of abamectin (MK-936) on natural populations of selected invertebrates in man-made ponds

    Med. Entomol. Zool.

    (1997)
  • Altenburger, R., Arrhenius, A., Backhaus, T., Coors, A., Faust, M., Zitzkat, D., 2013. Ecotoxicological combined...
  • A.S. Braun et al.

    Ecotoxicological effects of Vertimec® 18EC on plankton

    J. Braz. Soc. Ecotoxicol.

    (2012)
  • W.C. Campbell

    Ivermectin and Abamectin

    (1989)
  • Environment Canada

    Guidance Document on Control of Toxicity Test Precision Using Reference Toxicants. Report EPS 1/RM/12

    (1990)
  • E. Capri et al.

    Prediction of environmental concentrations (PECs) by mathematical model application in Europe

    Pestic. Outlook

    (1998)
  • P. Carriquiriborde et al.

    Aquatic risk assessment of pesticides in Latin America

    Integr. Environ. Assess. Manag.

    (2014)
  • J.E. Casida et al.

    Neuroactive insecticides targets, selectivity, resistance, and secondary effects

    Annu. Rev. Entomol.

    (2013)
  • L.E. Castillo et al.

    Ecotoxicology and pesticides in tropical aquatic ecosystems of Central America

    Environ. Toxicol. Chem.

    (1997)
  • Cheminova, 2016. Freely accessible via http://www.adapar.pr.gov.br/arquivos/File/defis/DFI/Bulas/Inseticidas/kraft.pdf...
  • X.D. Chen et al.

    Individual-and population-level toxicity of the insecticide, spirotetramat and the agricultural adjuvant, destiny to the Cladoceran, Ceriodaphnia dubia

    Ecotoxicology

    (2010)
  • A. Coors et al.

    Predicting the aquatic toxicity of commercial pesticide mixtures

    Environ. Sci. Eur.

    (2011)
  • Coors, A., Löffler, I., Noronha-Jänsch, P., Weisbrod, B., Schoknecht, U., Sacher, F., 2013. Ecotoxicological combined...
  • A. Coors et al.

    Predicting acute and chronic effects of wood preservative products in Daphnia magna and Pseudokirchneriella subcapitata based on the concept of concentration addition

    Environ. Toxicol. Chem.

    (2014)
  • C. Cox et al.

    Unidentified inert ingredients in pesticides: implications for human and environmental health

    Environ. Health Perspect.

    (2006)
  • M.A. Daam et al.

    Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides

    Ecotoxicology

    (2010)
  • N.J. Diepens et al.

    Effect of pesticides used in banana and pineapple plantations on aquatic ecosystems in Costa Rica

    J. Exp. Biol.

    (2014)
  • L.C. Do Hong et al.

    Tropical ecotoxicity testing with Ceriodaphnia cornuta

    Environ. Toxicol.

    (2004)
  • [EC] European Commission, 2006. Draft Assessment Report (DAR) – Public version – Initial risk assessment provided by...
  • [EC] European Commission, 2006. Draft Assessment Report (DAR) – Public version – Initial risk assessment provided by...
  • FOCUS surface water scenarios in the EU evaluation process under 91/414/EEC. Report of the FOCUS workgroup on surface...
  • [FRAC] Fungicide Resistance Action Committee

    FRAC Code List©*2016: Fungicides Sorted by Mode of Action (including FRAC Code Numbering)

    (2016)
  • Cited by (0)

    View full text