Acute and chronic toxicity of glyphosate compounds to glochidia and juveniles of Lampsilis siliquoidea (Unionidae)

This study examined the toxicity of various forms of glyphosate, one of the most widely used pesticides in the world, and a surfactant commonly used with glyphosate (MON 0818) to glochidia and juveniles of the freshwater mussel Lampsilis siliquoidea.

Found to be acutely toxic to L. siliquoidea were the commercial product Roundup®, technical-grade IPA (isopropyl-amine) salt of glyphosate, IPA salts, and the surfactant MON 0818. L. siliquoidea glochidia and juveniles were not acutely sensitive to technical grade glyphosate or the commercial product AquaStar®.

L. siliquoidea experienced acute toxicity to MON 0818 (24 hr LC50 for glochidia was 0.6 mg/L); in fact as of the time of this report L. siliquoidea had the most acute sensitivity to MON 0818 of any organism tested. L. siliquoidea glochidia and juveniles had 48 hr LC50s for Roundup® in the range of 3-6 mg/L, and 48hr LC50s for Glyphosate IPA from 5-8.3 mg/L. In agricultural regions the concentrations of glyphosate in streams have been measured in the mg/L range, meaning these are environmentally relevant LC50s.

Because technical-grade glyphosate with IPA salts was acutely toxic to L. siliquoidea but technical grade glyphosate without IPA salts was not, the IPA component was likely the toxic component. This may have been due to the liberation of ammonia from the amine group of the IPA salts. AquaStar® has IPA salts as one of its components, but it was not found to be acutely toxic. This is possibly due to the interaction of other components of AquaStar® with the amine group of the IPA salts.