39 



Potential for Toxic Conditions 



Physical features of some watercourses are such that fish 

 could evade toxicants if their senses alerted them in time. 

 Goodnight (194-2) detennined that fish avoided high concentrations 

 of pentachlorcphenol but did not avoid lower concentrations which 

 proved toxic. Due to similarities between pentachlorophenol, 

 other chlorinated phenols, and chlorinated catechols, it is probable 

 that fish would avoid only the higher concentrations of chlorinated 

 phenols and catechols but not lower concentrations which might prove 

 toxic. 



Results and discussion have indicated that chlorinated catechols 

 and phenols uncouple oxidative phosphorylation. Since these various 

 chlorinated phenolic compounds apparently affect metabolism in a 

 similar way it would be expected that a toxic situation could occur 

 in a watercourse even thoiogh none of the individual compounds were 

 at a toxic level. Studies of this type of situation (Herbert and 

 Shvjrben, 1964) indicate that toxicities of some compounds are 

 additive by using the equation Pg/Pr^ + Qg/Q^ = 1, where P^ and Q^, are 

 threshold concentrations of two toxicants and Pg and i^g are 

 concentrations to which the fish are exposed. For example, toxicity 

 of phenol-zinc, zinc-ammonia, copper-ammonia and phenol-ammonia 

 mixtures could be prsdicteu from the equation (Herbert and Vandyke, 

 1964^ Sprague and rlamsay, 1965) . Supposedly the equation could be 

 extended to include three or more compounds. According to Herbert 

 and Shurben (1964), ammoniiua chloride and zinc sulphate mixtvires 

 suited the equation, but histological examination indicated that 

 lethal concentrations of the two substances did not cause the same 

 symptoms as lethal concentrations of only one of the toxicants. 

 They therefore concluded that sublethal effects of each toxicant 

 could sum vithin the fish and thereby kill it. 



