Toxicity of the amphoteric surfactant, cocamidopropyl betaine, to the marine macroalga, Ulva lactuca

The degradation of the synthetic, amphoteric surfactant, cocamidopropyl betaine (CAPB) and its toxicity to the marine macroalga, Ulva lactuca, has been evaluated using several different physiological test end-points over different periods of exposure up to 120 h. Droplet surface angle measurements revealed that, following a period of acclimation of about 24 h, CAPB began to degrade and that primary degradation was complete within 120 h. Effective quantum yield (∆F/F_m′) and relative growth rates (RGRs) were the most sensitive measures of phytotoxicity, with CAPB concentrations at and above 10 mg l⁻¹ eliciting irreversible, time-dependent and/or dose-dependent responses. Cell membrane damage, estimated from measurements of ion leakage, was detected only at a concentration of 40 mg l⁻¹ after 48 h of exposure to CAPB but by 120 h damage was evident at all measured concentrations above 10 mg l⁻¹. These observations suggest that both CAPB and its metabolites are intrinsically toxic to U. lactuca. The findings of this study are discussed in terms of the environmental consequences of applying CAPB to control harmful algal blooms.