As mentioned above, many parent PAHs contain alkyl side groups including naphthalenes, phenanthrenes, fluorenes, chrysenes, dibenzothiophenes, and others, which increase the hydrophobicity and bioaccumulation potential with increasing alkylation. Consequently, when only a limited set of parent PAH compounds are considered, the bioaccumulation and toxicity potentials can be severely underestimated.
Only a few studies have highlighted the degree to which organisms are exposed to alkylated PAHs. Additionally, very little information on the metabolism of alkylated PAHs is available, which would be useful for understanding the accumulation of these compounds in organisms and those at higher trophic levels. Many studies, including large monitoring programs, have found that alkylated PAHs often comprise a very large percentage of the total PAH concentration in stomach contents or tissues.
Very few studies have examined the toxicity of alky-lated PAHs, even though they are expected to be as toxic (or more toxic) than their respective parent compound. As an example, one study found that a single oral dose of Prudhoe Bay Crude oil produced adverse effects in herring gull nestlings. Upon further analysis, these authors found that the fraction containing the methyl homologs of several HPAHs was the most toxic. Another fraction containing alkylated LPAHs did not appear to have any effect on growth, indicating that the alkyl homologs of the four- to six-ring PAHs were more toxic than the alkyl homologs containing two or three rings.
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