Nonylphenol polyethoxylate adjuvant mitigates the reproductive toxicity of fomesafen on the freshwater snail Lymnaea stagnalis in outdoor experimental ponds

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 Lymnaea stagnalis was investigated, with particular attention to the reproductive performances 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 nontoxic in L stagnalis. Fomesafen was mixed with the adjuvant in the 3:7 ratio recommended for agricultural uses (nominal herbicide concentrations of 22 and 40 microg/L in laboratory and mesocosm, respectively). In mesocosms, multiple application of fomesafen, leading to maximal herbicide concentrations of 60.33 +/- 2.68 microg/L in water, resulted in 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 microg/L at the end of the 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 nonionic surfactant activity of NPEO that prevented fomesafen from reaching the snails.

Preparation and characterization of fomesafen ionic liquids for reducing the risk to the aquatic environment

“…19,20 Although fomesafen can be degraded by microbes in soil and has a very low potential ecological risk to soil ecosystems, it negatively interferes with the reproduction of freshwater snails and its media lethal concentrations are 0.12 mg L À1 and 1.51 mg L À1 to green algae Selenastrum capricornutum and marine diatom Skeletonema costatum, respectively. [20][21][22] In addition, there is report of approximately 200 fish (channel catfish, crappie, largemouth, and redear sunfish) dying following a legal application to a soybean site, which was related to fomesafen runoff. 20 Therefore, the reduction of the application dosage and concentration in the aquatic systems in nature is very important to ensure the security of the aquatic environment from fomesafen application.…”