Relative phytotoxicity of purified, biodegradable surfactants was determined by observing their effects on the growth of orchid seedlings in vitro. Pronounced phytotoxic effects occurred on culture media containing high concentrations of surfactants. Concentration of ionies above 100 ppm were most damaging and also caused a 90% or greater reduction of interfacial tension. Nonionic ethoxylates reduced growth and viability at lower concentrations than ionies, but larger percentages of seedlings survived at 1000 ppm levels of these agents, which were less efficient in reducing interfacial tension. No correlation was found between biological effects and surface tension data but a coincidence may exist between interfacial tension reduction by ethoxylates and increased phytotoxicity.
A number of purification procedures for surface active agents are presented as an Appendix.