The Effect of Herbicide Formulations and Herbicide-Adjuvant Mixtures on Aquatic Food Web Species of the Sacramento-San Joaquin Delta, California, USA.

Herbicides have recently been designated as one of the most frequently detected chemical types in aquatic systems. We evaluated the effect of the herbicide formulations Clearcast® (active ingredient imazamox) and Galleon® SC (active ingredient penoxsulam), in conjunction with the adjuvant Agri-dex®, on the diatom Thalassiosira pseudonana and the copepod Eurytemora affinis and whether their application in invasive aquatic weed control has acutely negative effects on important delta food web species. Herbicide-adjuvant mixtures were more toxic than herbicide formulations alone.

Toxicity of herbicides to cyanobacteria and phytoplankton species of the San Francisco Estuary and Sacramento-San Joaquin River Delta, California, USA.

The herbicides glyphosate, imazamox and fluridone are herbicides, with low toxicity towards fish and invertebrates, which are applied to waterways to control invasive aquatic weeds. However, the effects of these herbicides on natural isolates of phytoplankton and cyanobacteria are unknown. Three species of microalgae found in the San Francisco Estuary (SFE)/Sacramento-San Joaquin River Delta (Delta) (, , and ) were exposed to the three herbicides at a range of concentrations in 96-well plates for 5-8 days.

Sub-lethal effects of herbicides penoxsulam, imazamox, fluridone and glyphosate on Delta Smelt (Hypomesus transpacificus).

Concerns regarding non-target toxicity of new herbicides used to control invasive aquatic weeds in the San Francisco Estuary led us to compare sub-lethal toxicity of four herbicides (penoxsulam, imazamox, fluridone, and glyphosate) on an endangered fish species Delta Smelt (Hypomesus transpacificus). We measured 17β-estradiol (E2) and glutathione (GSH) concentrations in liver, and acetylcholinesterase (AChE) activity in brain of female and male fish after 6 h of exposure to each of the four herbicides. Our results indicate that fluridone and glyphosate disrupted the E2 concentration and decreased glutathione concentration in liver, whereas penoxsulam, imazamox, and fluridone inhibited brain AChE activity.