PARENT SESSION

2A - Mixture toxicity
Poster Hall
8:30 AM - Monday, 28 April 2003
Chair: Hermens, J.¹, ¹
Co-chair: Toy, R.², Backhaus, T.³, ^{2 3}

(MOP/71) Mitigating effects of a polyethoxylated nonylphenol-based adjuvant (Agral® 90) on the toxicity of fomesafen (diphenyl-ether herbicide) in the pond snail Lymnaea stagnalis.

Jumel, A.¹, Coutellec, M.-A.^{1, 2}, Cravedi, J.P.³, Lagadic, L.¹, ¹ INRA EQHC, Rennes, France² UMR 6553 Ecobio, Rennes, France³ INRA Xenobiotiques, Toulouse, France

ABSTRACT- The influence of nonylphenol polyethoxylates (NPEO), formulated as the adjuvant Agral® 90, on the effects of the diphenyl ether herbicide fomesafen in the pond snail was investigated, with particular attention to growth and reproduction, and underlying energetic and hormonal processes. Separate short-term exposures to low concentrations of fomesafen and fomesafen-Agral® mixture were performed in the laboratory. Outdoor experimental ponds (mesocosms) were used for long-term exposures to higher chemical concentrations. At the concentrations used in the studies, NPEO were known as non-toxic in L. stagnalis. Fomesafen was mixed with the adjuvant in the 2.3 ratio recommended for agricultural uses (nominal herbicide concentrations of 22 and 40 g/L in laboratory and mesocosm, respectively). In mesocosms, multiple application of fomesafen, leading to maximal herbicide concentrations of 60.33 ± 2.68 g/L in water, resulted in inhibited growth, reduced number of egg-masses and altered glycogen metabolism in contaminated snails. These changes, as well as affected steroid-like levels in fomesafen-exposed snails, support the hypothesis of impaired neuroendocrine functions. When Agral® 90 was added to the herbicide, results obtained in mesocosms showed that the adjuvant softened the impact of fomesafen. In mesocosms treated with the fomesafen-Agral® mixture, significantly lower herbicide levels were found in the water (30.33 ± 14.91 g/L at the end of contamination period). Consequently, internal exposure of the snails to fomesafen was reduced when the herbicide was mixed with the adjuvant. Mitigation of the effects of fomesafen by the adjuvant may therefore result from non-ionic surfactant activity of NPEO that prevented fomesafen from reaching the snails.

Key words: diphenyl-ether herbicide, mixture toxicity, aquatic mesocosm, reproduction