Toxicity evaluation of three pesticides on non-target aquatic and soil organisms: commercial formulation versus active ingredient

Abstract

The Ecological Risk Assessment of pesticides requires data regarding their toxicity to aquatic and terrestrial non-target species. Such requirements concern active ingredient(s), generally not considering the noxious potential of commercial formulations. This work intends to contribute with novel information on the effects of short-term exposures to two herbicides, with different modes of action (Spasor^®, Stam Novel Flo 480^®), and an insecticide (Lannate^®), as well as to corresponding active ingredients (Glyphosate, Propanil and Methomyl, respectively). The microalga Pseudokirchneriella subcapitata (growth inhibition), the cladoceran Daphnia magna (immobilisation), and the earthworm Eisenia andrei (avoidance behaviour) were used as test species. Both herbicides were innocuous to all test organisms at environmentally realistic concentrations, except for Stam and Propanil (highly toxic for Pseudokirchneriella; moderately toxic to Daphnia). Lannate and Methomyl were highly toxic to Daphnia and caused Eisenia to significantly avoid the spiked soil at realistic application rates. The toxicity of formulations either overestimated (e.g. Stam/Propanil for P. subcapitata) or underestimated (e.g. Stam/Propanil for D. magna) that of the active ingredient.

Appendix: Methodological details for use of an organic solvent in E. andrei exposure to Propanil

The use of organic solvents such as acetone overcomes difficulties in toxicant solubility and often facilitates the full accomplishment of test requirements (OECD 2004). Standard guidelines for toxicity testing with aquatic organisms recommend such a procedure for poorly soluble substances (e.g., OECD 2004; ISO 2005). In the avoidance assay with Propanil, water holding capacity was first adjusted (see “Materials and methods”) in both soils (dual-choice: control and test soils). The contaminated half of each replicate was then spiked with a stock solution prepared by dissolving the appropriate amount of Propanil in 1 ml pure acetone (final acetone concentration: 5 ml kg⁻¹ dry soil). Test soil was thoroughly mixed immediately after spiking, and it was left to rest (to allow evaporation of acetone) for ca. 1 h prior to the placement of earthworms. In order to discard the hypothesis that acetone could be toxic to earthworms, a dual-choice design (see “Materials and methods”) was employed using clean soil vs. soil spiked with 1 ml acetone. Experiments were carried out in decaplicate, following the conditions and procedures described for avoidance tests (see “Materials and methods”—Earthworm avoidance assays’). A mean net response of −0.12 ± 0.15 (SE) was obtained and it was found not to deviate significantly from zero (t test, P > 0.05). Hence, acetone did not induce avoidance behaviour of earthworms, indicating that the use of acetone as organic carrier, to test the toxicity of poorly soluble chemicals, produces valid test results.