Laboratory and field tests for risk assessment of metsulfuron-methyl-based herbicides for soil fauna.

Metsulfuron-methyl is one of the most used sulfonylurea herbicides, being applied alone in pre-emergence and with a mineral oil (as adjuvant) in post-emergence. In risk assessment of pesticides, ecotoxicity tests have been applied to assess the effects of products and mixtures under laboratory conditions, but they are limited in their ecological relevance when compared to field assessments. Considering the differences between laboratory and field exposure, and the lack of data on the effects of metsulfuron-methyl in natural soils, this study consisted in a set of tests to assess the ecotoxicity of this herbicide applied alone, combined with an adjuvant (mineral oil) and the adjuvant applied alone, both under laboratory and field exposure, with artificial and natural soil respectively. Reproduction tests with four non-target soil invertebrates species were performed in laboratory, while two experiments were performed in field evaluating avoidance behaviour, feeding activity, mesofauna abundance and pesticide residual. Laboratory results showed that metsulfuron-methyl alone is not a threat to soil fauna on the recommended doses. However, the presence of mineral oil as adjuvant showed ecotoxicity to Eisenia andrei, Enchytraeus crypticus and Proisotoma minuta on laboratory tests. Field evaluations indicated that metsulfuron-methyl and the adjuvant do not impaired the feeding activity of the soil fauna. The low abundance of native communities could be related to soil management. Results showed that laboratory and field evaluations are necessary to better understanding of the effects of pesticides to soil fauna and adjuvant addition should be considered on pesticides risk assessment.

Screening effects of metsulfuron-methyl to collembolans and earthworms: the role of adjuvant addition on ecotoxicity.

Metsulfuron-methyl is a common active ingredient recommended for use in pre- and post-emergence control of annual grasses and broadleaf weeds in crops, usually applied with mineral oil as adjuvant to enhance its efficiency. Despite the increasing use of this herbicide, there are no information on its ecotoxicity effects to soil fauna. Avoidance and lethality tests were performed with earthworms and collembolans using tropical artificial soil contaminated with formulated products Ally® (600 g L-1 metsulfuron-methyl) and Assist® (756 g L-1 mineral oil) as adjuvant. Lethality test with earthworms showed no difference when tested with or without adjuvant. When Ally® was tested alone, it caused avoidance behavior only at high concentrations (5000 and 10,000 times field predicted dose). However, Assist® addition changed the response of soil invertebrates increasing the avoidance even at field predicted doses. The toxicity of the adjuvant was confirmed in tests exposing collembolans and earthworms to Assist® alone resulting in avoidance behavior. The results clearly show that the addition of mineral oil enhanced the ecotoxicity of metsulfuron-methyl. This study provides an important contribution to the knowledge on the toxicity of metsulfuron-methyl and indicates that adjuvants should be considered in risk assessment of pesticides, considering that under field conditions, these products are applied together.