The Influence of pH on Toxicity

The behaviour of the hydrogen ion represents a fundamental chemical principle and is critical to the toxicity profile of many ionizable substances. Corrosivity is a dramatic, destructive and obvious result of very acidic or very 

The definitive determinant of toxicity is a function of the concentration of the ultimate toxicant at the target site for a long enough period of time, which is governed by the time course of action (kinetics) and the response to the interaction at the target site (dynamics). 

Toxic responses cannot occur unless an organism is exposed to a chemical and the ultimate toxicant reaches its site of action. The route by which the toxicant enters an organism can profoundly influence its ultimate fate. The major routes of exposure are inhalation, ingestion, dermal contact, and uptake by other species-specific organs, for examples gills in fish. 

For toxicants that are weak acids and bases, the pH partition theory can be used to determine the extent of ionization of a toxicant that in turn can help characterize the extent of absorption. The Henderson-Hasselbach equation relates pH to the percent of compound ionized, as follows  

Non-ionized compounds are absorbed more efficiently than compounds that are ionized. The pH is an obvious influence in the ratio of ionized to un-ionized species and therefore the pH changes along the gastrointestinal tract, which profoundly influences the extent of absorption at a particular 

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Konemann, W.H., Musch, A. (1981) Quantitative structure-activity relationships in fish toxicity studies. Part 2 The influence of pH on the QSAR of chlorophenols. Toxicology 19, 223-228. 

Chromium (Cr+6) TT luminescent bacteria are exposed to assess the influence of pH speciation of chromium on toxicity response. B (Villaescusa et ah, 1997)... 

Saarikoski, J., Viluksela, M. (1981) Influence of pH on the toxicity of substituted phenols to fish. Arch. Environ. Contam. Toxicol. 10, 747-753. 

Welsh, P.G., J. Lipton, C.A. Mebane, et al. 2008. Influence of flow-through and renewal exposures on the toxicity of copper to rainbow trout. Ecotoxicol. EnviroTL Sc. 69 199-208. Wilde, K.L., J.L. Stauber, S.J. Markich, et al. 2006. The effect of pH on the uptake and toxicity of copper and zinc in a tropical freshwater alga Chlorella sp.). Arch. Environ. Contam. Toxicol. 51 174-185. 

Dalela, R.C., S. Rani, and S.R. Verma. 1980. Influence of pH on the toxicity of phenol and its two derivatives pentachlorophenol and dinitrophenol to some fresh water teleosts. Acta Hydrochimica et Hydrobiologia 8 623-629. 

Ma, W.C. 1984. Sublethal toxic effects of copper on growth, reproduction and litter breakdown activity in the earthworm Lumbricus rubellus, with observations on the influence of temperature, and soil pH. Environ. Pollut. 33A 207-219. 

Water quality parameters, such as pH, temperature, hardness, and salinity, can influence the effects of contaminants on aquatic life. The toxicity of TNT decreases slightly with increasing pH and temperature, but is not significantly affected by hardness [39], The persistence of TNT in the environment is limited, and several biological and physical processes (photolysis, hydrolysis) influence its environmental fate [39], The photolysis half-life of TNT appears to be season and latitude dependent, as it ranged from 14 h at latitude 20 in summer to 84 h at latitude 50 in winter in the northern hemisphere [40], The aquatic toxicity of several photo- and biodegradation products of TNT has been studied. Pink water obtained by constant illumination of a TNT solution was more toxic than the TNT solution to P. promelas using... 

The influence ofthe pH ofbody fluids and organs on the hydrolysis of heavy metal salts as well as their solubility, reactivity, and the toxicity ofthe hydrolysis products. 

As mentioned above, metallic toxicity is largely influenced by pH. However, the effects of pH vary depending on the type of species and the type of metals present. The pH of test water should be controlled carefully with consideration of such effects. 

Ryan, A.C., J.R. Tomasso, and S.J. Klaine. 2009. Influence of pH, hardness, dissolved organic carbon concentration, and dissolved organic matter source on the acute toxicity of copper to Daphnia magna in soft waters Implications for the biotic ligand model. Environ. 

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