Toxic effects of juncusol,a marsh plant phenolic extract,on estuarine fish and shrimp

Juncusol, a phenolic compound, was isolated from the black needlerush, $\text{Juncus roemerianus}$. Different concentrations of this extract were tested for toxicity against selected species of estuarine fish and grass shrimp. Juncusol was ten times more toxic to the various species of fish than to grass shrimp. At 2.0 ppm concentration all fishes tested were killed within 36 hr. One hundred per cent mortality in the grass shrinmp occured at 20 ppm during 95 hr exposure. The LC₁₀, LC₅₀, and LC₉₀ concentration for juncusol were calculated for grass shrimp and for juvenile sailfin molly.