Using Property Guidelines to Design for Reducing Acute Aquatic Toxicity

Using Property Guidelines to Design for Reducing Acute Aquatic Toxicity 

Acute toxicity to aquatic species can be rationalized mechanistically by one of two types of interactions nonspecific mechanisms (called narcosis) or specific mechanisms. The latter involves specific interactions, such as covalent electrophilic reactions with biological macromolecules, or specific noncovalent interactions that cause toxicity, such as uncoupling of phosphorylative oxidation, among others. Most chemicals that are toxic to aquatic organisms are narcotic. Some have both narcotic and specific mechanisms. A narcotic chemical enters the cellular membranes of the organism and, by its mere presence, causes perturbations in the membranes to the extent that alterations in the function of the membranes occur, resulting in toxicity. 

According to McFarland [26], aquatic toxicity can be considered the result of penetration of toxicant into biophases and its interaction with one or more biochemical sites of action. Thus, he and others have postulated that toxicity is a function of the ability of the chemical to enter biophases and its ability to react with cellular compounds. Bioavailability of chemicals in fish has been shown to be related to chemical flux across fish gills [27], an identified exposure pathway. Flux across fish gills is in turn related to the ability of the chemical to partition between organic and aqueous phases, which is usually correlated with the its octanol-water partition coefficient (logPo/w) [28]. It is therefore not surprising that the acute toxicity of narcotic chemicals has been shown to be related to their propensity to accumulate in the membranes, and hence their logPe/w [29]. 

It has been shown that the correlation coefficients of the two most useful attributes to acute toxicity of various aquatic species are strikingly similar [32]. Table 13.3 shows 

Property Fathead minnow (96 h) Japanese medaka (96 h) Daphnia magna (48 h) P. sub capitata (72 h) 

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