Abstract
Imazethapyr is an herbicide that is used in a variety of crops worldwide, including soybean and corn. The aim of the present study was to evaluate the biomarkers responses of adult Leptodactylus latinasus exposed to the formulation Pivot®H (10.59% imazethapyr) in the laboratory at concentrations and under conditions that simulate two potential field exposure scenarios: an immersion in field runoff (Scenario 1: 10mg/L) and a direct exposure to the droplets emitted by spray noozles (Scenario 2: 1000mg/L). In both scenarios, the experimental procedure involved completely immersing the frogs over a period of 15s. Different endpoints were evaluated at several ecotoxicological levels 48 and 96h after the herbicide exposure. These included individual (biometric indices and behavior alterations), histological (liver pigments and lesions), biochemical (catalase, glutathione system and cholinesterase activities) and genotoxic effects (micronuclei induction and nuclear abnormalities). Forty-eight hours after imazethapyr exposure, frogs submitted to Scenario 1 presented an inhibition of liver glutathione-S-transferase activity, whereas histological alterations and increased hepatic cholinesterase levels were observed in frogs exposed under Scenario 2. Ninety-six hours after exposure to the imazethapyr formulation, frogs from the Scenario 1 treatment presented a decrease in liver melanin and hemosiderin, increased hepatic catalase activity and micronuclei induction. For their part, frogs exposed to Scenario 2 presented a decrease in the hepatosomatic index, an increase in liver alterations, melanin reduction and micronuclei induction. The multivariate analysis enables correlations to be made between biomarkers of different organizational level in exposed anurans. Our result indicates that real exposure to imazethapyr formulations under field conditions may pose a risk to Leptodactylus latinasus populations living in the agroecosystems.
Highlights
Pesticide applications are deemed critical to maintaining high agricultural output
The responses after 48 h of each endpoint showed a decrease in GST activity in S1, while there was an increase in liver tissue alterations (HV and enlargement of sinusoids (ES)) as well as AChE activity in S2
After 96 h, the observed effects were a marked decrease in the hepatosomatic index (HSI), melanin and hemosiderin and a concomitant increase in CAT activity and MNs frequencies in S1, while there was a marked decrease in the HSI and melanin added to an increase in tissue alterations (HV and ES)
Summary
Pesticide applications are deemed critical to maintaining high agricultural output By constrast, they can cause adverse effects in non-target organisms because they share target sites similar to the sites of action of pesticides (Howarth, 2000; Köhler and Triebskorn, 2013). The imidazolinones are a group of widely used broad-spectrum herbicides employed for selective pre- or post-emergence weed control in a variety of crops. These herbicides fall into the class of acetolactate synthase (ALS)-inhibitors, an enzyme involved in the synthesis of branched-chain amino acids (Tan et al, 2005; Kawai et al, 2007; Lin et al, 2007). Imidazolinones are considered to have low toxicity in non-target animals included in the categories as slightly toxic (Class III) for the U.S Environmental Protection Agency (U.S EPA) (USEPA, 1989) and unlikely to be dangerous for the World Health Organization (Kegley et al, 2020)
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