Naphthenic acids toxicity

Naphthenic acids are only slightly toxic to mammals hut are toxic to fish, bacteria, and wood-destroying insects. The lethal oral dose for humans is approximately 1 L. Naphthenic acid is not listed as a carcinogen. 

Definition Obtained by treating cobaltous hydroxide with naphthenic acid Properties Brn. amorphous powd. or bluish-red solid sol. in oxygenated soivs., oil, alcohol, ether insol. in water dens. 0.95 flash pt. 120 F autoignition temp. 529 F contains 6% Co Toxicology TWA 0.1 mg(Co)/m (fume, dust) LD50 (oral, rat) 3900 mg/kg mod. toxic by ing. TSCA listed... 

CAS 61790-14-5 EINECS/ELINCS 263-109-4 Synonyms Cyclohexanecarboxylic acid, lead salt Naphthenic acid lead salt Empirical C7H12O2 xPb Properties M.w. 1578.52 Toxicology LD50 (oral, rat) 5100 mg/kg, (IP, rat) 520 mg/kg poison mod. toxic by IP route mildly toxic by ing. questionable carcinogen tumorigen TSCA listed... 

Naphthenic acid are most significant environmental contaminants. They are comprised of a large collection of saturated aliphatic and alicyclic carboxylic acids found in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). Moreover, they are toxic components in refinery wastewaters and in oil sands extraction waters. In addition, there are many industrial uses for naphthenic acids, so there is a potential for their release to the environment from a variety of activities. Studies have shown that naphthenic adds are susceptible to biodegradation, which decreases their concentration and reduces toxidty. 

In general, the complex and changing nature of mixtures of naphthenic acids make it difficult to predict toxicity. By determining the critical mechanism of toxicity of naphthenic acids, it might be possible to develop more effective predictive relationships to account for the toxic effects observed in living organisms exposed to naphthenic acids. 

In this study several models were used for non-polar compounds to aquatic and terrestrial species to determine the acute toxicity of selected naphthenic acids (Tables 3). 

The results of estimation of naphthenic acids for persistence, bioaccumulation and toxicity are presented in Table 2. The components of naphthenic adds are commonly classified by their structures and the number of carbon atoms in the molecule. 

Table 3. Experimental and predicted values of acute toxicity for some naphthenic acids.

Naphthenic acids can enter the environment from both natural and anthropogenic processes. Naphthenic acids are highly toxic, recalcitrant compounds that persist in the environment for many years, and it is important to develop efficient bioremediation strategies to decrease both their abundance and toxicity in the environment. However, the diversity of microbial communities involved in naphthenic acid-degradation, and the mechanisms by which naphthenic acids are biodegraded, are poorly understood. This lack... 

Frank, R.A., Fischer, K., Kavanagh, R., Burnison, B.K, Arsenault, G., Headley, J.V., Peru, K.M., Van Der Kraak G. Solomon, KR 2009. Effect of Garboxylic Acid Content on the Acute Toxicity of Oil Sands Naphthenic Acids. Environmental Science Technology, Vol. 43, pp. 266-271. 

Figure 35. Naphthenic acid concentrations and toxicity (Microtox 1C20) for (a) waters collected along the Athabasca River (from about 100 km upstream of Fort McMurray to the delta of Lake Athabasca), and (b) various waters at Syncrude s Mildred Lake Site. With time, the original toxicity and naphthenic acid levels in the fresh process waters (PW, SP) show a steady decrease when removed from fresh input of tailings (SS, 1, 3, and 5 years). Levels in the Athabasca River represent natural surface waters.

The levels of naphthenic acids in extraction waters are aeutely toxic to many aquatic biota [J36,147], Application of molecular toxicity methods, in which stress-inducible genes from E. coli are exposed to oil sands derived naphthenic acids, indicated that the main toxic response was indieative of eytotoxicity with osmotic stress and membrane disruption... 

The naphthenic acids in fresh tailings water show a direct dose response as shown in the Microtox bioassay results in Figure 37(c), where fresh surface zone water from the Syncrude s Mildred Lake Settling Basin was dilnted with deionized water. The initial tailings water, with a naphthenic acid concentration of 128 mg/L, was quite toxic (IC50 = 21% by voL), and not until it had been diluted to about 10% was the 1C50 greater than 100%. 

However, with ageing, the toxic response per unit of naphthenic acid decreases. From Fignre 38, the reduction in naphthenic acid content and of acnte toxicity with time for tailings waters, stored under aerobic conditions, is evident for an array of biota. Natural bioremediation processes are proceeding in the oil sands extraction waters, once they are removed from fresh input of process waters and maintained under aerobic conditions. This biodegradation process is the basis on which the both the wet and dry landscape reclamation options operate. With time, waters will be slowly released from the varions sinks (sand deposits, fine tails) in the end-lease landscape. If the rate of their release is less than the rate of the bioremediation processes, then the resulting waters should have the toxic components of the naphthenic acid group reduced to levels that will ensure the waters are neither acutely nor chronically toxic [136,142],... 

From an operational perspective, naphthenic acids are both beneficial and potentially a concern. As has been discussed earlier, the surface active properties play an important role in the efficiency of the bitumen separation methods from oil sands. These same surface active properties result in toxic responses to an array of biota that may affect the water... 

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