Fig. 13. Relationships between different toxicity profiles for a cluster of 54 sulphonic acids. Arrows go from the vehicle with the lower toxicity to the vehicle with the higher toxicity (i.e. ‘safer’ to ‘less safe’). Labels on the arrows indicate the number of compounds which are found for the vehicle pair to be less toxic : more toxic : no difference. Where two or more vehicles are not considered to show a difference in toxicity, a double headed arrow is used and the label indicates less toxic on the left : less toxic on the right : no difference.