Acute toxicity of the herbicide Maleic Hydrazide to the tadpoles of Bufo arenarum Hensel, 1867

MAMANI MORENO C.; BURBA J.L.; STADLER T.

Ribeirão Preto, Sao Paulo, Brasil

Congreso; 1st Ibero-American Meeting On Toxicology And Environmental Health; 2009

Introduction: Maleic  hydrazide (CAS: 1,2-dihydro-3,6-pyridazinedione) (MH), is widely used as a  plant growth retardant, applied as a foliar spray for control of undesired  sprouting of potatoes, carrots, garlic, etc. during storage. Bufo arenarum is a  natural inhabitant in South American agricultural ecosystems, commonly found in  irrigation water tanks, drainage channels and ditches. As much of the MH  application is likely to coincide with the aquatic larval phase of B. arenarum,  tadpoles can be exposed to MH through spray drift and contaminated water. Given  the important roles B. arenarum plays in aquatic and terrestrial food webs,  investigating the effects of MH residues on this organism is environmentally  relevant. Objective: The aim of this study was to evaluate the acute toxicity  of MH in immature forms of B. arenarum. Methodology: Toxicity tests were  conducted by exposing groups of ten tadpoles in 96-h static bioassays to  concentrations of 0.005; 0.01; 0.05; 0.1; 0.12; 0.14; 0.16; 0.18; and 0.20 g/L  MH and using three replicates per treatment. Mortality was assessed once every  15 minutes in the first hour and after 2, 12, 24, 48, 72 and 96 hours. Tadpole  mortality was used as bioassay endpoint and malformations in bioassay surviving  tadpoles and young frogs were recorded for up to 38 days after treatment. The  dose-response data were analyzed by using a probit procedure. Results: Tadpoles  of B. arenarum responded in a concentration-dependent manner to increasing  concentrations of waterborne MH and mortality occurred always within the first  30 minutes of exposure. The estimated 96 h LC50 of MH was 0.118 g/L and the  calculated NOEC was 0.08g/L. Morphological abnormalities in bioassay surviving  tadpoles and young frogs were not observed. Conclusion: Exposure of amphibian  tadpoles to varying concentrations of MH resulted in mortality. Toxicity was  observed even with concentrations that were smaller than those used in agricultural  ecosystems. Thus, chemical pollution from MH could be one of the causes for the  decline of amphibian populations.