The phytotoxicity of adjuvants depends on the amount of surfactant deposited per unit of leaf area, the penetration of the surfactant into the leaf, and the cellular toxicity. In this study we investigated the cellular toxicity by determining the leakage of electrolytes from potato discs. We included four adjuvant classes [alkylpolyglycosides (APG), polyoxyethylene fatty alcohols (FAL-EO), methylated polyoxyethylene fatty acids (FAC-EO-ME), and esterified polyoxyethylene glycerols (G-EO-E),]. In each class we included a lipophilic and a hydrophilic product by variation of the C-content of the alkyl chain (APG) or EO-content (other classes). Conductivity of the bathing media was measured at concentrations of 10-4,10-3,10-2,10-1, and 1% (w/v). A polyoxyethylene (10) nonylphenol was included as a reference compound. The cellular toxicity of the adjuvants started at concentrations >0.01% (FAL-EO and FAC-EO-ME) or >0.1% (APG).
The glycerol derivatives (G-EO-E) were not toxic at all concentrations tested. The FAC-EO-ME class of adjuvants was the most toxic class; on average 65% of the total electrolyte content of the discs was released within 3h. The FAL-EO and the APG adjuvants were less toxic excepted the C8-C10 APG giving a release of 56% at a concentration of 1%. In each adjuvant class the lipophilic product was less toxic than the more hydrophilic product. The results are discussed in relation to the physical-chemical properties of the adjuvants.